Buderus Manual on Trenchless Installation of Ductile Cast ... - Duktus

<strong>Buderus</strong> <strong>Manual</strong> 

Trenchless Installation 

of Ductile Cast Iron Pipes

The future is ductile 

Ductile cast iron pipe systems for drinking water supply and waste water disposal 

„The conditions may be complicated, 

but our ductile cast iron pipes, with their secure joints, 

can be laid without any problems.“ 

Stephan Hobohm of the 

Applications Engineering Division of 

<strong>Buderus</strong> Giesserei Wetzlar GmbH 

www.gussrohre.com

<strong>Buderus</strong> <strong>Manual</strong>

Trenchless Installation of Ductile Cast Iron Pipes 


on Trenchless Installation 

of Ductile Cast Iron Pipes

1. Introduction 

Introduction 

When the infrastructure of our present-day towns and cities was being created and 

developed, the typical feature of the construction sites was large numbers of men to do 

the work. Trenches for laying pipes were excavated by hand, the pipes were lowered 

into the trenches without any mechanical lifting gear and vast amounts of sand and backfill 

material were shovelled in by hand. The most widely used material for the pipes was cast 

iron and the joints between them were sealed with hanks of hemp and poured lead. 

Today, after more than 100 to 120 years, the networks of pipes that were laid at the 

time need to be rehabilitated and replaced. In those town and city streets where once 

upon a time there was plenty of space for pedestrians to stroll and elegant carriages to 

drive, there are now several lanes of dense motor traffic and kerbs that are blocked by 

parked cars, which means that delivery vehicles often double-park and cause further 

disruptions to the traffic. If the rehabilitation or replacement work on the existing 

network of pipes had to be done in conventional open-cut trenches in this case, the 

general interference with traffic would become almost total and it would be the 

community that had to suffer the additional costs of delays, exhaust and noise emissions 

and loss of retail income caused by the obstruction to public travel. 

It was therefore only logical for the first steps in the development of trenchless pipe 

installation techniques to be taken, as long as 30 years ago, in the densely populated 

areas of industrial towns, initially for the renovation or relaying of sewer pipes, which are 

generally situated on the lowest tier of the layers of pipes below the surface. Developers 

then transferred their attention more and more to the renovation and rehabilitation of 

drinking water and gas pipelines. A sector of industry devoted to trenchless installation 

grew up, with its own special machinery, installation techniques, technical rules and 

standards and of course, not least, its own pipes, which had to be suitable for these 

trenchless installation techniques. 

Over the past ten years, <strong>Buderus</strong> Giesserei Wetzlar GmbH, with its ductile cast iron 

pipe, has made a crucial and impressive contribution to these developments and it is the 

story of this contribution that the present manual wishes to tell. The intention is also to 

describe the present state of the art, or in other words what installation techniques the 

ductile cast iron pipe can be used for, what are the performance features that it has and 

who are some of the satisfied customers who have put its ability to perform to the test. 

Wetzlar, June 2008

Imprint 

Published by 


Sophienstraße 2 - 

D-3 7 Wetzlar 

Tel.: + 9(0) 1- 9 22 0 

Fax: + 9(0) 1- 9 1 13 

e-mail: export.gussrohrtechnik@guss.buderus.de 

www.gussrohre.com 

Authors: 

Dipl.-Ing. Steffen Ertelt, Dipl.-Ing. Stephan Hobohm, Dipl.-Ing. Lutz Rau, Wolfgang Rink 

of <strong>Buderus</strong> Giesserei Wetzlar GmbH 

Dr. Jürgen Rammelsberg 

Photo credits: 


Berliner Wasserbetriebe 

Karl Weiss GmbH & Co. KG, Berlin 

Fachgemeinschaft Guss-Rohrsysteme 

Tracto Technik GmbH & Co. KG, Lennestadt 

Frank Föckersperger GmbH, Aurachtal 

© <strong>Buderus</strong> Giesserei Wetzlar GmbH 

All rights reserved 

All illustrations and details of weights and measures are subject to change. As part of 

ongoing technical development, we reserve the right to make product alterations and 

improvements without prior notice.


Trenchless Installation of Ductile Cast Iron Pipes 

List of contents: 

1. Introduction ................................................................................ 

2. Properties of ductile cast iron pipes ........................................... 8 

3. Trenchless replacement of gas and water pipelines .................... 32 

3.1 Push-pull technique ................................................................... 3 

3.2 Auxiliary pipe technique ............................................................ 39 

. Burst lining technique ................................................................ 

. Horizontal directional drilling technique ................................... 

. Ploughing technique .................................................................. 8 

7. Pipe relining ............................................................................... 7 

7.1 Pulling-in technique ................................................................... 77 

7.2 Pushing-in technique ................................................................. 79 

8. Pulling-in after steered pilot drilling ........................................... 8 

9. A consideration of the economics of trenchless techniques ...... 92 

10. Technical data sheets ................................................................. 98 

11. Installation instructions .............................................................. 102 

List of contents 

7

Properties of ductile cast iron pipes 

2. Properties of ductile cast iron pipes 

2.1 The material 

Fig 2.1, 

Fountains in the park at the Chateau de Versailles 

8 

In the 17th century there were isolated 

instances where pipes made of cast iron 

were used for laying water-pipes on estates 

belonging to the aristocracy, such 

for example as at chateaus and country 

houses, in parks, and so on (Fig. 2.1). 

In the 19th century, with the coming of the 

Industrial Revolution, towns and cities and 

industry began to develop. The growth in 

the population accelerated and there was 

thus a growing need for an infrastructure 

to be created based on pipes for drinking 

water, gas and sewage. 

Cast iron in the form of pig iron is produced by using coke to reduce iron ore in a blast 

furnace, a process known as smelting. A particularly important type of smelter used 

in foundry work is the cupola furnace in which scrap iron and steel and pig iron are 

smelted with coke. Another typical process for producing cast iron is smelting in an 

electric induction furnace. 

In these smelting processes, some of the carbon goes into solution in the liquid iron, 

as a result of which the melting point of the pure iron goes down from about 1 0°C 

to a figure of 11 0°C. This is the most important prerequisite for the industrial and 

economical processing of cast iron, because it allows the consumption of energy, refractory 

materials and mould materials to be reduced. The second advantage of the 

carbon dissolved in the iron comes into play when the molten cast iron solidifies: the 

contraction in the volume of the iron as it changes from the liquid to the solid state 

counteracts any increase in the volume of the dissolved carbon which crystallises out. 

Consequently, articles made of cast iron generally have a dense microstructure free of 

cavities. The disadvantage of the elemental graphite in the cast iron is that it reduces 

the strength and ductility of the pure iron. In the course of solidification, the dissolved 

carbon normally crystallises in the form of graphite lamellae.

At x 100 magnification, these graphite lamellae can clearly be seen in metallographic 

micro-sections (Fig. 2.2). Under the scanning electron microscope, the space-filling 

structure of the graphite lamellae is very clear (Fig. 2.3). 

Fig. 2.2 Fig. 2.3 

Fig. 2.4 

Fig. 2.5 

The material 

The lamellar graphite, which has no strength of its 

own, interrupts the matrix of metal in which it is embedded 

and thus causes the relatively low strength 

which cast iron has. At the same time, this internal 

structure also gives the material poor ductility: its 

fracture behaviour is brittle. The modelled representation 

shown in Fig. 2. simulates the internal 

notch effect which is caused by the concentration 

of stress lines at the tips of the lamellae. This is the 

reason for the poor ductility of grey cast iron. 

Some 0 years or so ago, the form in which the 

graphite crystallises was successfully altered by a 

metallurgical treatment of the melt with metals with 

a high affinity for oxygen (cerium, magnesium). In a 

melt of cast iron in which the graphite would originally 

have solidified in lamellar form, it solidifies in a 

spheroidal form if a small amount (about 0.0 %) of 

the above metals is added. 

9


Compared with lamellar graphite, graphite in a spheroidal form reduces the internal 

stress concentrations in the base metal. The strength of cast iron containing spheroidal 

graphite is considerably higher than that of cast iron containing lamellar graphite and it 

also has the ability to deform plastically under external mechanical loads. 

The associated modelled representation is shown in 

Fig. 2. . The stress lines are less tightly packed between 

the spheroids of graphite than they were at the 

tips of the lamellae. This gives the material the ability to 

undergo elastic and plastic deformation before it actually 

fails. Behaviour of this kind by a material is called 

ductile. 

This significant change in the properties of the mate- Fig. 2.6 

rial has meant that spheroidal graphite (i.e. ductile) cast 

iron has been able to replace steel in many areas of 

mechanical engineering. 

Experts on the pipe networks used for supplying gas and water were very quick to 

appreciate the advantages that the ductile behaviour of the new material gave: if overstressed 

mechanically, brittle pipes fail by what are called egg-shell fractures, where 

large openings, which allow vast amounts of water to escape and cause considerable 

consequential damage, appear all at once. When the failure of the material is ductile, 

a high proportion of the fracturing energy is converted into deforming energy. Highly 

deformed parts of the workpiece are always found close to the fracture. Crack propagation 

proceeds more slowly and only a small amount of water escapes through the 

comparatively small opening that it produces. Underscouring as a consequence of eggshell 

fractures is now a thing of the past. In the mid-nineteen-sixties, ductile cast iron 

superseded grey cast iron as a material for pipes in the gas and water supply industry. 

In 1973, Albrecht Kottman published details of the trials he had conducted to demonstrate 

the outstanding energy of deformation of ductile cast iron pipes. Fig. 2.7 shows 

the test rig he used: two-meter-long pipes of a nominal size of DN 100 and of different 

materials were set up on two supports as beams stressed in bending and were 

stressed by a force applied at mid-span. The stress-strain curves plotted in these trials 

are shown in Fig. 2.8. 

Whereas a DN 100 pipe of lamellar graphite cast iron fractured at a load of approximately 

six tonnes with almost no deformation (= brittly), the pipe of ductile cast iron 

bowed by 17 centimetres under approximately the same force before it failed. 

10

10 3 kp cm 

Fig. 2.7 

Steel Ductile Grey Asbestos PVC 

cast cast cement 

iron iron 

Kottmann defined the integral of the 

area below these curves as energy 

of deformation and compared this 

property of pipes made of different 

materials in the bar chart shown in 

Fig. 2.7. He was able to show in this 

way that the energy of deformation 

of pipes made of ductile cast iron was 

higher by more than a power of ten 

than that of, for example, pipes made 

of grey cast iron. 

Fig. 2.8 

Grey 

cast 

iron 

Test rig 

Asbestos 

cement 

PVC 

Ductile 

cast iron 

Seamless steel 

Welded steel 

The material 

11


2.2 How the pipes are produced 

Casting techniques of the kind which had been developed in the Middle Ages, above all 

for casting works of art and bells and also for casting guns, were a prerequisite for the 

development of a technology for producing high-quality pipes. Initially pipes were cast 

in horizontal moulds where the moulds were also split horizontally. This meant that 

there was a limit to how long the pipes could be, given that at the casting temperature 

of some 1300°C and under their own weight, the cores used to form the hollow centres 

of the pipes would bend, which also limited the uniformity of the wall thickness of 

the pipes. Pipes dating from this early period of manufacture can be recognised by the 

two lines of flash on opposite sides of their outer surface, which formed in sand moulds 

on the plane marking the division between the top and bottom halves of the moulds 

(Fig. 2.9). 

With the increasing demand for cast iron 

pipes for supplying water and gas in the 

rapidly expanding towns and cities in the 

second half of the 19th century, the carousel 

casting process was introduced, in 

which the sand moulds were arranged 

upright in casting carousels in such a way 

Fig. 2.9 

that a semi-continuous procedure became 

possible. In this process, the moulds, in 

the form of undivided metal mould boxes 

matched to the shape of the pipe, were 

initially placed in position individually and 

later on in rotary racks, to allow work to 

go on in a continuous flow. The cores to 

produce the hollow centres in the pipes 

were rammed onto metal core spindles 

with the help of metal core bushes. There 

was an increase in the overall length of the 

Fig. 2.10 

pipes and the flash at the mould division 

disappeared. This process was used by <strong>Buderus</strong> from the time when pipe production 

began in 1901 until 192 . Hundreds of thousands of kilometres of pipes dating from this 

period of production are still giving faithful service below the ground. 

A particularly important milestone in the course of further development was the invention 

of the centrifugal casting process (Fig. 2.11). In 192 , this process was successfully 

introduced throughout Europe, including at <strong>Buderus</strong>. One of its principal features is 

12

Fig. 2.11 

How the pipes are produced 

a permanent metal mould (a chill mould) 

which is cooled from the outside by water 

and which does not need a thermally insulating 

covering. One chill mould can be 

used to cast as many as several thousand 

pipes, depending on their nominal size. 

The sudden quenching of the liquid cast 

iron against the water-cooled chill mould 

produces just a single solidification front, 

facing towards the wall of the chill mould, 

which makes the microstructure particularly 

fine-grained and dense. After heat 

treatment to transform the microstructure 

(Fig. 2.12), it is possible to obtain appreciably 

higher strength in the grey cast 

iron pipes than can be obtained in pipes 

cast in sand moulds. The length of the 

Fig. 2.12 

pipes went up to five or six metres, and the wall thickness went down and became 

more uniform. Shortly after the centrifugal casting process made its breakthrough, the 

new joint-making technique was invented (see section 2.3), and after that the leadsealed 

socket could only be a thing of the past. 

13


In today‘s typical pipe foundry, the cast iron for producing the pipes is smelted in a cupola 

furnace, is adjusted to a preset composition by tailored metallurgical procedures 

and is raised to the requisite casting temperature. This is followed by the treatment 

with magnesium to produce ductile cast iron and the melt, having been treated in this 

way, is then at once cast into pipes. 

The outcome of the developments that took place over the 0 years between 1920 

and 1970 was that the tensile strength of pipes could be raised and their weight and 

wall thickness halved. As development of the production technology has continued, 

and above all with modern-day systems for controlling the casting machines, it has 

been possible for a considerable further reduction to be made in the wall thickness of 

the pipes. Account has been taken of this in the product standards EN [2.1] and 

EN 98 [2.2], where a shift can be seen from classification by wall thickness to classification 

by pressure class. 

1

2.3 Development in the joint-making techniques 

When cast iron pipes first began to be used, one of the primary concerns was sealing 

the individual butt joints between the pipes. In 172 , Jacob Leupold had already 

described in his book [2.3] a mixture of various powders and substances containing 

organic constituents to produce a sort of putty that was halfway elastic. 

Fig. 2.13 

Development in the joint-making techniques 

In the period which saw the growth 

of centralised systems of water supply 

(18 0-1930), the cast iron pipes were fitted 

with a socket that had to be packed; 

it was sealed with tarred hanks of hemp 

and poured lead (Fig. 2.13). When they 

are being made, joints made with packed 

sockets call for great skill and reliability on 

the part of the fitters doing the job. Because 

the sealing material is very inelastic, 

Fig. 2.14 

the joint must not be subject to any movements. 

Bedding which will not be disturbed and support for the pipe which does not 

allow any movement are essential for long-term freedom from leaks. 

Rolling ring seals made of rubber were initially introduced for gas pipes in 18 0 and 

from 18 3 on they came into use for water pipes. As from 1910 there were some initial 

trial pipes in Stuttgart which used a precursor of the screw-gland socket joint but the 

advantages of this joint were not appreciated for the time being. It only made its real 

breakthrough in the early 1930‘s (Fig. 2.1 ) and in doing so it represented a milestone 

in pipe-laying in that since then the elasticity of seals of vulcanised rubber has allowed 

joints to move to a certain degree. 

1


The characteristic feature of the screwgland 

socket joint for the range of nominal 

sizes from DN 0 to DN 00, and of the 

bolted-gland socket joint (Fig. 2.1 ) which 

is more suitable for larger nominal sizes, 

is that a gasket of elastic rubber is compressed 

by mechanical means. This seals 

the joint against gaseous and liquid media. 

In the early 19 0‘s, <strong>Buderus</strong> introduced 

the TYTON ® socket joint. With this design 

of joint, all that is needed apart from 

the two pipes to be joined is a profiled 

gasket. When the inserting end is slid into 

the socket containing the gasket, the gasket 

is compressed and thus automatically 

makes the seal. Fig. 2.1 shows this joint, 

for which there is a standard in the form 

of DIN 28 03 [2. ]. Extensive checks have 

shown that this joint will remain sealed for 

decades even when subject to dynamic 

angular deflection movements. 

Their design means that the socket joints which have been described are not locked 

against longitudinal forces. At changes of direction, stop-ends, changes of cross-section 

and branch pipes, the internal pressure of the water generates longitudinal forces 

which have to be dissipated into the ground in some suitable way. Traditionally, this has 

been done by using concrete counter-bearings. These are sized in such a way that the 

size of the rear face prevents the permitted pressure per unit area on the in-situ soil 

from being exceeded. The rules for the sizing of counter-bearings made of concrete are 

given in DVGW Arbeitsblatt GW 310 [2. ]. The smaller and smaller amounts of space 

that are available in the ground below our towns and cities has made it necessary for 

this technique to be gradually abandoned and to be replaced by joints which are traction-resistant. 

1 

Fig. 2.15 

Fig. 2.16 

Traction-resistant joints are locked against longitudinal forces yet are able to hinge at 

the same time. The principle on which they operate is that the resistance of the earth 

is brought into play by slight movements of the fittings and the pipes connected to 

them. The document giving the technical rules for the use of such longitudinal force-fit

joints is DVGW Arbeitsblatt GW 3 8 of 

June 2002 [2. ]. The current designs are 

shown in section in this document together 

with the associated performance data. 

A distinction is made between joints which 

are locked by friction and joints which are 

positively locked. With its BRS ® frictionlocking 

joint and its BLS ® positive-locking 

joint, <strong>Buderus</strong> offers two innovative solutions 

in this case. In the BRS ® frictionlocking 

joint (Fig. 2.17), sharp, hardened 

stainless steel teeth bite into the surface 

of the inserting end and this produces 

the frictional connection. There are also 

friction-locking designs for bolted-gland 

socket joints. 

In the BLS ® positive-locking joint, a bead 

of weld metal is applied to the surface of 

the inserting end either in the factory or 

on site and appropriate force-transmitting 

members are supported against this 

bead and thus transmit the longitudinal 

force from one pipe to the next (Fig.2.18). 

Fig. 2.17 

Fig. 2.18 

Entwicklung der Verbindungstechnik 

The development of these socket joints, which are locked against longitudinal forces 

but at the same time able to hinge, to their present-day standard of maturity was essential 

to the development of modern-day trenchless techniques for installing pressure 

pipelines. In almost all of the trenchless installation and renovation techniques which 

are described in the present manual, it is a hinged string of pipes locked against longitudinal 

forces which is pulled into the final route of the pipeline. Whereas in the series 

of standards which applied previously, namely DIN 28 00 et seq., it was just the pipes 

and fittings which were exactly described, in the European standards which now apply, 

namely DIN EN for water pipes and DIN EN 9 for sewage conduits and pipes, 

there is a new aspect which is considered, namely the functional requirements they 

have to meet. With their exact descriptive specifications, the earlier national standards 

provided what was needed for technical delivery conditions. The additional aspect 

dealt with by the European standards, namely the functional requirements which the 

17


pipe system and its joints have to meet, specifies what the performance of the pipe 

system and its joints has to be. In the type tests which are laid down for this purpose, 

the components and their joints are tested for the following: 

• Sealing of the components against internal water pressure 

• Sealing of joints against positive internal pressure when subject to loads at the crown 

resp. angular deflection 

• Sealing of joints against negative internal pressure when subject to loads at the crown 

resp. angular deflection 

• Sealing of joints against positive external pressure when subject to loads at the 

crown. 

The longitudinal force-fit joints also have to pass a dynamic test in which the internal 

pressure alternates between PMA and PMA- for 2 ,000 load cycles. The functional 

requirements described and the related type tests have been included in the technical 

rules of the DVGW (the German Technical and Scientific Association on Gas and 

Water) which are given in Arbeitsblatt GW 3 8. In view of the importance that highquality 

longitudinal force-fit restrained joints will have in the future for trenchless pipe 

installation, the supplementary requirement of an externally monitored type test was 

introduced when the above document was revised in 2002. As well as this, all designs 

have to be listed by the following characteristic performance parameters: 

• allowable component operating pressure (PFA) 

• allowable angular deflection. 

With these particulars plus an indication of the externally monitored type test, there 

being sets of particulars which are representative of respective ones of four groups of 

nominal sizes, the planning engineer has the right tool for selecting the design giving 

safety against tractive forces that is best suited to a specific task. 

18

Longitudinal force-fit joints and technical rules for trenchless installation 

2.3.1 Longitudinal force-fit joints and technical rules for trenchless installation 

In the period between 2002 and 200 the drawing up by the DVGW of a set of technical 

rules for quality assurance for trenchless installation and renovation techniques 

also took place. The quality of pipelines which are installed by these techniques is 

affected not only by the effects due to the soil but also by the following parameters, 

which have to do with the pipes themselves: 

• permitted tractive forces 

• minimum radius of curves. 

These parameters have to be measured and documented, to ensure that the planned 

operating life will not be reduced by components that were damaged at the outset 

due to over-stressing. For the most important materials, they are listed in the sets 

of tables which can be found in the appendices to the documents mentioned, these 

materials being. 

• ductile cast iron 

• cross linked polyethylene (PE-X) 

• PE 100 

• St 37 steel. 

Allowance is made for the dependence of the permitted tractive stress on temperature 

and for the time for which it lasts in the case of the thermoplastic materials. In this 

way, the permitted pulling-in forces have to be decreased by a quarter for pulling-in 

times of more than 20 hours, and when pipes are at a wall temperature of 0°C the 

permitted force has to go down by 30% compared to a wall temperature of 20°C. 

Further reductions have to be envisaged when pipes follow curved paths. In contrast 

to these reductions due to routeing and temperature, for ductile cast iron pipes 

there are increases that can be made in the permitted forces when the pipes run in 

a straight line with no appreciable angular deflections. The temperature of the pipe 

wall is immaterial with ductile cast iron pipes. For the longitudinal force-fit BLS ® joint, 

Table 2.1 gives the following parameters 

• permitted tractive force 

• angular deflection which is possible 

• minimum radius of curves. 

The figures for the permitted tractive force were taken from the results of externally 

monitored internal-pressure tests conducted as part of the standard type tests, as 

indicated in the headings of the columns in the table. 

19


Table 2.1: Permitted tractive forces, angular deflections which are possible, and radiuses 

of curves for ductile cast iron pipes with BLS ® joints (source: DVGW Arbeitsblatt 

GW 321 [2.7] and <strong>Buderus</strong> Giesserei Wetzlar GmbH (BGW) 

To the experts at the Berlin water supply company Berliner Wasserbetriebe (BWB), 

who were pushing ahead with the trenchless replacement of the old systems of grey 

cast iron pipes, the above figures of GW 321 appeared to be too low. Hence, as a joint 

endeavour of the cast iron pipe industry, the Karl Weiss company and BWB, axial tractive 

tests were carried out on pipes of nominal sizes ranging from DN 100 to DN 200, 

with no internal pressure, until they began to fail [2.8]. 

20 

Nominal size Component 

DN [mm] operating pressure 

[bar] 1) 

Permitted tractive 

force Fperm [kN] 2) 

Possible 

DVGW BGW 

angular 

deflection of 

sockets3) Minimum radius 

[°] 

of curves [m] 

80* 110 70 11 9 

100* 100 100 1 0 9 

12 100 1 0 22 9 

1 0 7 1 200 9 

200 3 230 3 0 8 

2 0 308 37 8 

300 0 380 380 8 

00 30 8 0 3 11 

00 30 8 0 8 0 3 11 

00 32 1200 1 2 2 172 

700 2 1 00 1 0 1. 230 

800 1 - 1 0 1. 230 

900 1 - 18 1. 230 

1000 10 - 1 0 1. 230 

1) Basis for calculation was wall thickness class K9. Higher pressures and tractive forces 

are possible in some cases but must be agreed with the pipe manufacturer. 

2) When pipelines follow straight paths (max. deflection of 0.5° per pipe joint), the tractive 

forces can be raised by 50 kN. High-pressure locks are required for DN 80 - DN 250. 

3) When of the nominal dimensions 

* Wall thickness class K10


The results obtained in these tests showed there to be a threefold safety margin in 

comparison with the figures given in Table 2.1. FEM calculations carried out by Prof. 

Bernhard Falter [2.9] showed very good agreement with the experimentally determined 

figures for permitted tractive force. The very safe nature of the figures which 

were given for the permitted tractive forces on positive-locking joints in ductile cast 

iron pipes in the DVGW rules had two consequences: 

1. In its internal technical rules, BWB made a very large increase in the permitted tractive 

force from the figures given in the DVGW rules. This was because practical experience 

of a wide variety of kinds had convinced it of the high performance of the joints 

(see Table 2.2). 

2. A footnote was added to the tables in the DVGW rules saying that, with pipelines 

following straight paths and with an angular deflection of less than 0. ° ( = a radius of 

curvature of 87 metres), the permitted tractive force could be increased by 0 kN 

(see Table 2.1) 

Table 2.2: Permitted tractive force for positive-locking joints in cast iron pipes 

(source: internal standard WN 322 of Berliner Wasserbetriebe) 

Nominal size 

DN 

[mm] 

Component 

operating 

pressure PFA 

[bar] 1) 

Permitted tractive 

force F perm 

[kN] 2) 

Capacity for angular 

deflection 

of sockets [°] 

Minimum permitted 

elastic 

bending radius 

R min [m] 

80 100 2) 3 11 

100 2 0 1),2) 3 11 

1 0 0 320 1),2) 3 11 

200 0 00 1),2) 3 11 

2 0 3 00 2) 3 11 

300 30 00 2) 3 11 

00 2 8 3 11 

1) Determined by tractive tests (see report) 

2) The tractive forces given apply only to Berliner Wasserbetriebe and to DN 80 - DN 250 BLS ® 

joints with high-pressure locks. 

21


In the bar chart (Fig. 2.19), the figures from Table 2.1 for the maximum permitted tractive 

force on ductile cast iron pipes with BLS ® joints are compared with those for other 

materials for water pipelines. Of all the current materials for water pipelines, <strong>Buderus</strong> 

Giesserei Wetzlar GmbH‘s ductile cast iron pipes with positive-locking BLS ® joints 

22 

Material 

PE-Xa SDR 11 pipes 

PE 100 SDR 11 pipes 

St 37 steel 

Ductile cast iron, 

BLS ® joints 

Fig. 2.19: Maximum permitted tractive forces of different materials. Source: DVGW 

100 

have the highest permitted tractive forces. This allows installation pits to be spaced 

further apart when ductile cast iron pipes are being used and thus makes the pipes 

more economical without the need for safety to be sacrificed in any way. Additional 

increases, both in the operating pressure and in the permitted tractive force, are possible 

by increasing the class of wall thickness, but special agreements have to be made 

with our Applications Engineering Division for this purpose. 

150 

200 

300 

400 

100 

0 

600 

500 

400 

300 

200 

Nominal Size 

700 

Tractive 

force [kN]

2.3.2 Making the BLS ® joint 

Making the BLS ® joint 

For the trenchless installation of ductile cast iron pipes, the technical rules of the 

DVGW agree with what is specified in <strong>Buderus</strong> Giesserei Wetzlar GmbH‘s installation 

instructions in laying down the use of positive-locking joints. 

The circumstances under which friction-locking joints may fail are, above all, when 

there have been a number of angular deflection movements of the kind which may occur 

on steered directionally drilled runs when there are a number of curves in opposite 

directions along the run. This is because there are tractive forces which alternately 

relieve the load on the teeth of the retaining segments when these movements occur. 

There is no fear of this happening on runs which follow a straight path. Nevertheless, 

to prevent any risk, the use of positive-locking joints has been laid down for trenchless 

installation techniques. There is an additional advantage in that the maximum permitted 

tractive forces can be transmitted in this way. 

The <strong>Buderus</strong> positive-locking BLS ® system makes it possible for the two connecting 

processes which may be referred to as 

• „making a seal“ and 

• „locking“ 

to be separated and made into two separate steps which have to be performed one after 

the other and which can be checked. 

In the first step it is thus the TYTON ® joint which is made, following the installation 

instructions (see section 10): the socket and the inserting end having been cleaned, the 

gasket is inserted in the retaining groove in the socket by its hard-rubber claw. The circumference 

of the gasket is deliberately made larger than the circumference of the sealing 

surface with which it mates in the groove, and this means that the seal is subject to a 

pre-loading. Because of this, particularly with large nominal sizes, it may be helpful for a 

second fold to be made in the gasket on the opposite side. The two small folds can then 

the pressed flat without any trouble. The checking step which then follows ensures that 

the retaining claw on the gasket is pressed fully into the retaining groove around the entire 

circumference and is nowhere spaced away from the locating bead (Fig. 2.20). The 

faces of the gasket and inserting end which slide against one another are then given a thin 

coat of the lubricant which is supplied by <strong>Buderus</strong> with the joint and the inserting end is 

inserted in the socket square with it (i.e. with no angular deflection). Depending on the 

nominal size of the pipe, the axial force required to compress the bead on the gasket can 

be applied with a crowbar, a laying tool or the hydraulic digger. 

23


Fig. 2.20 

When joints are being made with a hydraulic digger, a suitable interlayer, e.g. a length 

of squared-off timber, must be placed between the pipe and the bucket of the digger. 

The pipe must be pressed in gently and sufficiently slowly for the gasket to have time to 

deform. Regardless of what equipment is selected to make the joint, pipes and fittings 

must be lined up so that they are concentric and square to one another. 

Locking 

The pipe remains square to the socket and is pressed into the latter until the welding 

bead is resting against the internal locating bead. This ensures that there is room for the 

locking members. Depending on how many there are, these are inserted though the 

openings in the end-face of the socket and are distributed around the circumference 

to the right and left. In the size range from DN 80 to DN 00 the locking members 

are locks (Fig. 2.21) whereas in the range from DN 00 to DN 1000 they are segments 

of a flat, planar form (Fig. 2.22). In the case of the locks, a distinction has to be made 

between the „left“ and right“ types, and these have to be inserted as directed in the 

installation instructions. With trenchless installation techniques and in high-pressure 

applications, an additional high-pressure lock is required. When the fitting of the locking 

members has been completed, a rubber catch fitted in the opening that is still clear 

in the end-face of the socket stops the locking members from shifting. 

2 

Wrong 

Right

Fig. 2.21 

Left lock 

Catch 

Right lock 

High-pressure lock 

With nominal sizes from DN 00 to 

DN 1000, the planar locking segments 

are inserted in the axial direction through 

the twin openings in the end-face of the 

socket and are then moved to be evenly 

spaced around the circumference. To 

simplify the locking process, the openings 

are preferably positioned to be at the 

crown of the pipe (Fig. 2.23). Once all the 

locking segments have been inserted in 

the gap in the socket, they are shifted as 

a whole around the circumference sufficiently 

far for none of the humps to be visible 

through the openings in the socket. 

The segments are fixed by a clamping strap 

and locked by gently pulling the pipe out of 

the joint until the welding bead comes to 

rest against the segments. An extra-strong 

metal clamping strap has proved useful 

in directional drilling projects involving a 

number of changes of direction (Fig. 2.2 ) 

A detailed description of how the various 

components are dealt with and used 

can be found in the operating instructions 

(section 11). 

Making the BLS ® joint 

Fig. 2.22 

Fig. 2.23 

Fig 2.24 

2


Table 2. shows the average assembly times required by a practised team of one or 

two pipe layers to make a BLS ® joint. The differences are the result of the different 

possible ways in which the joint can be protected. In the majority of pipe replacement 

operations, the joints are made for one length of pipe at a time in a pipe-assembling pit 

dug for the purpose. After the step of making the joint, the pipe string is pulled forward 

by the length of one pipe. If the on-site logistics are organised in the optimum way, it 

is possible to achieve speeds of installation of 0 to 0 metres an hour for the lower 

range of nominal sizes. It is impossible to achieve speeds of this kind with welded joints 

between pipes, especially if one bears in mind that with pipes of ductile cast iron using 

BLS ® joints the maximum permitted tractive force can be applied, in full, immediately 

the joint has been made and there is no need to wait for any cooling times. 

Table 2. : Average assembly times for the BLS ® joint 

2 

Nominal size Number of 

fitters 

Assembly time 

with no joint 

protection 

[min] 

Assembly time 

when a protective 

sleeve is 

used [min] 

Assembly time 

when shrink-on 

sleeves are used 

[min] 

DN 80 1 1 

DN 100 1 1 

DN 12 1 1 

DN 1 0 1 1 

DN 200 1 7 17 

DN 2 0 1 7 8 19 

DN 300 2 8 9 21 

DN 3 0 2 9 10 23 

DN 00 2 10 12 2 

DN 00 2 12 1 28 

DN 00 2 20 22 3 

DN 700 2 22 - 37 

DN 800 2 2 - 0 

DN 900 2 28 - 3 

DN 1000 2 30 -

2.4 Inside and outside protection 

Inside and outside protection 

Hand in hand with the introduction of ductile cast iron, there was also a rapid development 

in systems for inside and outside protection. Nowadays, pipes, fittings and 

accessories of ductile cast iron are all supplied complete with linings and coatings of a 

wide variety of types as an integral part of the product. The nature of the protection is 

governed by the conditions of installation and operation. 

2.4.1 Outside protection 

The grey cast iron pipes of the period from the end of the 19th century to the mid- 

20th century were endowed with their legendary long life by dipping them in liquid tar 

or asphalt, but the use of tar was discontinued at the end of the 1970‘s, roughly at the 

same time as ductile cast iron was introduced. As from the 1970‘s, dip-coating with tar 

was superseded by coating with bituminous paints. This was supplemented, or its field 

of application extended, by zinc coating (introduced later, as from the early 1970‘s) and 

by coatings of plastic-modified cement mortar (from 1978 on). More recently, the place 

of bituminous paints has also been taken by epoxy resin coatings. 

Because of the enormous importance it has for the use of ductile cast iron pipes in trenchless 

installation techniques, the cement mortar coating will be looked at in detail at this 

point. The cement mortar coating was initially developed chiefly as an outside protection 

for ductile cast iron pipes when they were going to be installed in stony ground, where 

it would have been expensive to get hold of sand or non-stony soil to bed the pipes 

in. The characteristic features of a coating of this kind are its high mechanical strength 

and resistance to chemicals, high impact resistance and high strength of adhesion. These 

requirements were decided on in consultation with the users and have been combined 

with the requisite methods of testing in DIN 30 7 -2 [2.10]. To implement the European 

construction product directive, a European standard, DIN EN 1 2 [2.11] has been laid 

down for cement mortar coatings for ductile cast iron pipes. 

In this connection, it will be recalled that the technical rules for conventional pipelaying 

give detailed requirements that the nature of the pipeline zone has to meet in 

order to safeguard the pipeline components against damage and deformation. In the 

first place, the bedding layers have to be produced from non-stony soil in such a way 

that the pipes rest down evenly over their entire length. The wedge-shaped space 

between the pipes and the bedding layers has to be evenly packed with non-stony 

soil, and any changes in the position of the pipe have to be avoided when this is done. 

27


The trench then has to be infilled layer by layer with non-stony soil at the sides, next 

to the pipe, and this has to be compacted as directed by the stress analyst, before finally, 

after 30 centimetres of non-stony soil has been dumped in and compacted over 

the crown of the pipe, the requirements become rather less stringent (Fig. 2.2 ). 

Main infill 

Direct cover zone 

Lateral infill 

Upper bedding layer 

Lower bedding layer 

Fig. 2.25 

DVGW Arbeitsblatt W 00-2 [2.12] provides an overview of the grain-sizes of filling 

and bedding materials for be used for various pipe materials. Under it, ductile cast 

iron pipes can be bedded in materials with a maximum grain size of 100 millimetres. 

The aim and intention of all the requirements is to ensure that the pipes will produce 

a pipeline of exactly circular cross-section in which there are no unacceptably high 

stresses in the walls of the pipes. This is the only way in which the long operating life 

that is desired can be achieved. 

Let us now consider the bedding conditions for a pipe which is installed by a trenchless 

technique: it is true that the customer will have a general knowledge of the ground he 

has, but he will certainly not be able to rule out the possibility of stones or other sharp 

objects being present along the run, against which the pipe will rub while it is being 

pulled in. With the burst lining technique for example, the new pipe is pulled through 

28 

Surface 

Walls of trench 

Height of cover 

OD 

Bedding 

Depth of trench 

Pipeline zone

Inside and outside protection 

the collection of sharp-edged fragments that once formed the old grey cast iron pipe. 

With the directional drilling technique, some of the supporting fluid may soak away 

through gaps in the soil, thus producing interruptions in a bed that was formerly even. 

This may result in settlement of the cover, or in short: trenchless techniques are carried 

out „out of the public eye“ as it were, and there is thus no controlling eye which 

can check that the stringent requirements which apply to the conventional open-cut 

techniques are in fact satisfied. 

It is clear that what has to be used in the „black box“ that the trenchless techniques 

represent is the most rugged pipe which has the coating able to withstand the highest 

mechanical loads. The <strong>Buderus</strong> ductile cast iron pipe, which has, comparatively 

speaking, the highest energy of deformation of all the types of pipe for water pipelines 

(see section 2.1), has the best prerequisites 

for undamaged installation under the 

uncheckable conditions that exist with 

the trenchless techniques. At the same 

time the positive-locking BLS ® joint, with 

its high permitted tractive forces, allows 

installation pits to be spaced at long intervals 

without any risk of the pipes failing 

when they are being pulled in. 

Ductile cast iron pipes with BLS ® restrained joints 

and cement mortar coatings 

2.4.2 Inside protection 

As mentioned in the preceding section, the use of tar and asphalt as both an outside and 

an inside protection for cast iron pipes was discontinued in the 19 0‘s. 

Whereas bituminous paints were then used for outside protection, an entirely new path 

was taken in the case of inside protection in the form of a lining of cement mortar. 

Depending on the application, what are available nowadays for the inside protection 

of ductile cast iron pipes are cement mortar linings based on blast furnace cement for 

drinking water applications or ones based on alumina cement for sewage applications. 

At <strong>Buderus</strong> Giesserei Wetzlar GmbH, 

coatings of these two variant types are applied 

to the inside of the pipe by the rotary 

centrifugal process to DIN 2880. 

This process gives the cement mortar lining 

a very high abrasion resistance. Even 

rates of flow of up to 20 m/s for the medium 

carried are no problem. 

Water is life 

29


2.5 Reference documents 

[2.1] DIN EN 

Rohre, Formstücke, Zubehörteile aus duktilem Gusseisen und 

ihre Verbindungen für Wasserleitungen – Anforderungen und 

Prüfverfahren 

[Ductile iron pipes, fittings, accessories and their joints for water pipelines 

– Requirements and test methods] 

[2.2] DIN EN 98 


ihre Verbindungen für die Abwasser-Entsorgung 

Anforderungen und Prüfverfahren 

[Ductile iron pipes, fittings, accessories and their joints for sewerage 

applications – Requirements and test methods] 

[2.3] Leupold, J.: 

Theatrum machinarum hydrotechnarum der Wasserbaukunst; 

Leipzig 172 

[2. ] DIN 28 03: Rohre und Formstücke aus duktilem Gusseisen – 

Steckmuffen-Verbindungen – Zusammenstellung, Muffen und Dichtungen 

[Ductile iron pipes and fittings - Push-in joints; survey, sockets and gaskets] 

[2. ] DVGW-Arbeitsblatt GW 310: Widerlager aus Beton; 

Bemessungsgrundlagen (Entwurf 2007) 

[Concrete abutments: principles of sizing (draft of 2007)] 

[2. ] DVGW-Arbeitsblatt GW 3 8: Längskraftschlüssige Muffenverbindungen 

für Rohre, Formstücke und Armaturen aus duktilem Gusseisen oder Stahl 

[Longitudinal force-fit restrained joints for ductile cast iron and steel pipes 

and fittings] 

[2.7] DVGW-Arbeitsblatt GW 321: Steuerbare horizontale 

Spülbohrverfahren für Gas- und Wasserrohrleitungen – 

Anforderungen, Gütesicherung und Prüfung 

[Steerable horizontal directional drilling methods for gas and water pipelines 

– Requirements, quality assurance and testing] 

30

Reference documents 

[2.8] Gaebelein, W. u. Schneider, M.: Grabenlose Auswechslung von 

Druckrohren mit dem Hilfsrohrverfahren der Berliner Wasserbetriebe 

[Trenchless replacement of pressure pipes by Berliner Wasserbetriebe‘s 

auxiliary pipe technique] 

GUSSROHRTECHNIK 38 ( 200 ), p. 8 

[2.9] Falter, B. und Strothmann, A.: Beanspruchungen und Verformungen in 

der TIS-K-Verbindung beim grabenlosen Auswechseln von duktilen 

Gussrohrleitungen 

[Stress and deformations in the TIS-K joint in the trenchless replacement of 

ductile cast iron pipelines] 

GUSSROHRTECHNIK 0 ( 200 ), p. 1 

[2.10] DIN 30 7 -2: Umhüllung von Rohren aus duktilem Gusseisen; 

Zementmörtel-Umhüllung 

[Cement mortar coating for ductile iron pipes; requirements and testing] 

[2.11] DIN EN 1 2: Rohre, Formstücke und Zubehör aus duktilem 

Gusseisen – Zementmörtelumhüllung von Rohren – Anforderungen 

und Prüfverfahren 

[Ductile iron pipes, fittings and accessories – External cement mortar 

coating for pipes – Requirements and test methods] 

[2.12] DVGW-Arbeitsblatt W 00-2: Technische Regeln 

Wasserverteilungsanlagen (TRWV); Teil 2: Bau und Prüfung, 09/200 

[Technical Rules – Water distribution systems; 

Part 2: Construction and testing, 09/200 ] 

[2.13] DIN 2880 Anwendung von Zementmörtel-Auskleidung für Gussrohre, 

Stahlrohre und Formstücke 

[Application of cement mortar lining for cast iron pipes, steel pipes 

and fittings] 

31

Trenchless replacement of gas and water pipelines 

3. Trenchless replacement of gas and water pipelines 

3 General 

There has been tremendous progress in the development of no-dig or trenchless techniques 

for installing new pressure pipelines and replacing old ones, particularly when this has to be 

done in inner city areas. There is an increasing trend towards the use of these techniques. 

Whereas large areas are covered with excavated soil when open-trench techniques are 

used, with trenchless techniques any nuisance of this kind is kept within acceptable limits. 

The following are some of the major advantages of trenchless techniques: 

• The digging-up of roads and earth-moving work are reduced by up to 80% or more 

(Fig. 3.1) 

• There is less excavated soil and bedding material to be transported (Fig. 3.2) 

• Less space is needed for the site equipment and facilities (this is particularly important 

in inner city areas, Fig. 3.3) 

• Sites can be confined to several small „points“ and it is therefore possible to cover the 

pit and put it out of reach of the weather, which benefits the quality of the product, 

i.e. the pipeline that is installed. 

Fig. 3.1 Space required for open-trench installation Fig. 3.2 Open-trench and trenchless installation: 

comparison of volumes of material transported 

32 

Open-trench 

installation 

Equipment 

Trenchless installation 

Volume of material transported 

Fig. 3.3 

Trenchless installation does not disrupt traffic

General 

What is said above is true of more or less all trenchless installation techniques. When 

these techniques are used for renovation, there are the following advantages as well: 

• the way of working does not create any vibrations and is quiet and this keeps the 

nuisance to traffic and to the public to a minimum 

• there is no damage to trees planted along the streets above the run of pipe. 

The major block of costs that are incurred when installing pipelines are the costs for 

below-ground work. Efforts to reduce these by developing new methods of installation 

have produced a wide variety of techniques which belong to the family of trenchless or 

no-dig installation and renovation techniques. 

The first of these was microtunneling, a steered pipe-jacking technique for the installation 

of new sewer pipes, this being the field of application where economic success 

could be achieved most quickly because of the considerable depths involved. What were 

generally of advantage in this case were sections normally measuring less than 0 metres 

in length extending in a straight line between two manholes. Since 198 the Berlin technique 

has been brought to a high level of sophistication. Today, the proportion of new 

sewer pipes that are installed by this method in Berlin is already 0%. 

The pipes mainly used for the construction of pressure pipelines are pipes that are connected 

into pipelines locked against longitudinal forces. What are used in this case are 

<strong>Buderus</strong> Giesserei Wetzlar GmbH‘s ductile cast iron pipes with their longitudinal forcefit 

BLS ® restrained joints. It was in the 1970‘s that longitudinal force-fit restrained joints 

began to be used to take the place of concrete counter-bearings. Their advantages for 

pulling in culvert pipes were recognised and began to be exploited at that time. This 

marked the beginning of trenchless installation techniques using ductile cast iron pipes. 

33


The greatest impetus to innovate in the field of trenchless replacement came from Berlin, 

where Germany‘s oldest systems of grey cast iron water pipes had by then been in 

use for more than 120 years and urgently needed to be renovated. There were external 

conditions in Berlin that made replacement more difficult and these took the form of the 

following requirements: 

1. The pipes are situated in the area where the roots of the trees at the edges of the 

pavements lie. The trees are strictly protected and under no circumstances may the 

roots be harmed. It is not possible for trenches to be dug for conventional laying. 

2. Replacement techniques where the old pipes remain in place along the run, either 

unbroken or in fragments, cannot be used. Any pipes or fittings which are not in use 

have to be removed in their entirety. 

This meant that the development of two special pipe replacement techniques, namely 

the press-pull technique and the auxiliary pipe technique, was almost pre-ordained; 

specifications serving as a foundation for both these techniques now exist as technical 

rules laid down by the DVGW in the form of Arbeitsblatt GW 322-1 [3.1] and Arbeitsblatt 

GW 322-2 [3.2]. Both techniques can be used for the trenchless replacement of 

pipelines, following the same route, with new pipelines of the same or larger nominal 

sizes (e.g. new DN 12 /1 0 pipes to replace old DN 100 ones, see Table 3.1), with the 

pipes making up the old pipeline being recovered either as fragments or as complete 

lengths. This gives the following advantages: 

1. Valuable raw materials are recycled. 

2. There is only minimal disruption of ground surfaces and nature. 

3. No new runs of pipe are installed in the space available below ground level. 

Table 3.1: Maximum increases in nominal sizes with trenchless replacement to 

GW 322-1 or GW 322-2 

3 

Nominal size of old pipes Maximum nominal size of new pipes 

DN 80 DN 1 0 

DN 100 DN 200 

DN 1 0 DN 200 

DN 200 DN 300 

DN 300 DN 00 

DN 00 DN 00

Other pluses that the two techniques have are these: 

General 

• There is no need for public-transport bus stops to be moved (see Fig. 3.3). 

• There is almost no interference with delivery traffic in streets where there are business 

premises. 

• Other utilities carried in pipes are not put at risk by excavation work. 

• Depending on the machinery used, whose maximum sound emission is less than . 

dB(A), the installation work is particularly „quiet“ and free of dust. It is even possible 

for work in residential areas to continue without any overnight breaks. 

Above all when installation work is being done in inner city areas, where there are very 

closely packed runs of pipe, intersecting pipelines and pipelines running in parallel are 

very much at risk when heavy-duty digging equipment is used in open trenches. This risk 

is cut to a minimum when trenchless replacement techniques are employed. 

The two techniques can both be used for supply pipelines of nominal sizes ranging from 

DN 80 to DN 00. What are required are: 

• a machine pit to hold the machinery, 

• an installation pit (about 7 metres long) for the new pipes, 

• intermediate pits for the house connections or branch pipelines. 

The distance between the intermediate pits depends on the nominal size of the old pipeline 

and on the condition it is in, on the nominal size of the new pipeline, on the machinery 

used, on the nature of the soil, on the trees present and their roots and of course on 

the conditions relating to traffic and the medium involved. Depending on the technique 

and the locality, the distance between the intermediate pits should not be more than 2 

to 0 metres. With a straight run of pipes or one with a radius of curvature of not more 

than 170 metres, the distance between the launch and arrival pits is normally from 100 

to 180 metres. Before the replacement operation, the old pipeline has to be taken out 

of service. The supply of the adjacent houses and other premises is maintained through 

temporary interim pipelines, the water from which is fed into the house connecting 

pipes, the ends of which have been closed off, in the pits for the house connections. 

3


3.1 The press-pull technique 

With this technique, the old pipe is pressed onto a breaker cone and shattered and is 

removed from the machine pit in fragments. The new pipes, which have longitudinal 

force-fit restrained joints – e.g. <strong>Buderus</strong> BLS ® joints – are hooked on at the end of the 

last old pipe by means of a traction head and are pulled into the cavity which is left free. 

The two steps take place simultaneously. 

Once the pits required have been dug and lined, the sections of old pipeline contained 

in them are cut out and removed. Specially prepared launch/assembly pits make it easier 

for the pipes to be installed and stop any fouling or contaminants from getting it (Fig. 

3. ). First of all, a traction linkage which can be coupled together is pushed through the 

old pipeline and anchored to an adjusting adapter at the end of the old pipeline, thus 

allowing the old pipes to be pressed out of the earth in the course of the replacement 

operation. No fragments are left in the bedding zone for the new pipeline. The new 

pipes are fastened to the adjusting adapter and, as the old pipe is pushed out, they are 

pulled in behind it at the same time. 

3 

Fig. 3.4 A DN 150 pipe in the pull-in pit

Fig. 3.5 Hydraulic unit 

The press-pull technique 

Via the adjusting adapter, the tractive forces from the traction linkage are applied to the 

end of the old pipeline as axial thrust forces. Hence the only traction-generated forces 

which act on the new run of pipe that is being pulled in are those generated by its own 

weight and the friction against its outer circumference. Arbeitsblatt GW 322-1 requires 

these forces to be continuously measured and recorded so that the new pipeline will 

not be stressed by tractive forces higher than those permitted. The measurement of the 

tractive forces is proof that the permitted load has not been exceeded during the replacement 

operation (for quality assurance). The socket acts in a similar way to a bore-widening 

device, which means that it is generally only at the socket that forces are generated by 

friction against its outer circumference. The -metre long main body of the pipe on the 

other hand, which is smaller in diameter, plays no part in generating any such frictional 

forces. Points of intended fracture, audio warnings of overloads, and similar provisions are 

not good enough as a guarantee of safety. 

The hydraulic press-pull unit is supported 

against the rear wall of the arrival pit via a 

steel abutment plate (Fig. 3. ). This plate 

is sized to suit the reaction forces and the 

nominal size of the pipes and there is only 

a small gap between it and the pipe so that, 

as far as possible, no earth will be forced 

into the pit. 

Launch pit 1st intermediate pit intermediate pit Machine pit/ 

arrival pit 

pull-in step 

with press-pull unit 

New 

pipeline 

Traction 

head 

Fig 3.7 The technique takes place in three steps 

Breaker 

cone 

Old 

pipeline 


linkage 

Abutment 

plate 

37


The hydraulic traction cylinders of the press-pull unit allow the old pipes to be pressed 

out without percussion or jerks. In the intermediate pits (Figs. 3.7 and 3.8), the old pipe 

is slid over a breaker cone or is smashed into pieces by an automatic pipe smasher (Fig. 

3.9). The fragments are conveyed to the surface in bins. In the final pull-in step, the old 

pipe, as it is pulled into the arrival pit, is generally broken as the traction cylinders made 

their backward stroke (Fig. 3.10). 

Fig. 3.8 Next step of the operation: 

Changing over the breaker cone in the intermediate pits 

Fig. 3.10 Final step: Changing the breaker cone over to the destination pit 

38 

2 nd pull-in step 

New pipeline Traction head Breaker 


New pipeline Traction head 

Old 

pipeline 


linkage 

3 rd pull-in step 

Old pipeline 

Abutment 

plate 

Fig. 3.9 

The hydraulic pipe smasher 

Abutment 

plate 

Breaker 



linkage

3.2 The auxiliary pipe technique 

The auxiliary pipe technique 

In the auxiliary pipe technique, the replacement process is divided into a number of steps. 

As in the press-pull technique which was described in section 3.3, in this case too a 

machine pit and a launch/assembly pit are required, together with the intermediate 

pits at house connections or branch pipes. The distances between the individual pits 

are similar. 

In the first step, the installing and intermediate pits are dug, the connecting pipes to 

houses are sealed off and the pipes to provide an emergency supply are connected up 

(Fig. 3.11). 

Machinery 

pit with pipe 

replacing unit 

Hydraulics intermediate pit intermediate pit 

Pipe assembly/launch pit 

Auxiliary pipe 

Old pipe 

Old pipe 

Old pipe 

Fig. 3.11 Making the assembly/launch pit and cutting the old pipes in the intermediate pits 

Missing pieces of the old pipe, resulting from the removal of house connections or similar 

are replaced by transition pieces. Then, by means of auxiliary steel pipes connected by 

longitudinal force-fit restrained joints, the pressing unit presses the old pipes into the 

assembly/launch pit until they have all been removed (Fig. 3.12) 

Machinery 

pit with pipe 



Launch/assembly pit 


Old pipe 

Transition 

piece 

Old pipe 

Transition 

piece 

Old pipe 

Fig. 3.12 

Pressing out the first, second and third sections of the old pipe by means of an auxiliary pipe 

39


It may be helpful in this case for individual sections to be detached by means of hydraulic 

jacks before the entire run of old pipe is pushed through into the launch/assembly pit. 

Because sections measuring up to metres in length can be removed from this pit, the 

technique is also an obvious one to use for the replacement of old steel pipes, because 

these cannot be burst over a breaker cone (Fig. 3.13). 

Fig. 3.13 Full-length old pipes 

The whole of the last old pipe having been removed, the run is filled by the re-usable 

auxiliary pipes (Fig. 3.1 ). These now carry the loads from the top cover and the traffic 

load and thus safeguard the bore for the pipeline. 

Machinery 

pit with pipe 



Fig. 3.14 Auxiliary pipes occupying the whole of the run 

0 


Pipe assembly/launch pit

In the final stage of the operation, the new pipe is coupled to the auxiliary pipes present 

in the bore for the pipeline by means of a traction head with built-in facilities for measuring 

tractive force. The auxiliary pipes are pulled back into the machine pit and the new 

pipeline is thus drawn into the existing bore (Fig. 3.1 ). The assembly of the new pipes 

in the launch/assembly pit proceeds in parallel with the dismantling and removal of the 

auxiliary pipes in the machine pit. If a traction head which enlarges the bore is used, new 

pipes of larger sizes can be pulled in. Operations usually take place with a small oversize 

of 10 to 1 % on top of the outside diameter of the sockets. 

If the old pipe is unable to withstand the compressive forces which can be expected, it is 

cut in the intermediate pits and removed in short section. 

The permitted tractive forces for the new pipe and its joints must not be exceeded. 

Machinery 

pit with pipe 



Fig. 3.15 Pulling-back of the auxiliary pipe and pulling-in of the new one 

The auxiliary pipe technique 

Pipe assembly/launch pit 

Auxiliary pipe New pipe 

Traction head with forcemeasuring 

equipment 

1


3.3 Requirements for the new pipe 

The new pipe and its joints have to withstand high tractive forces and still have to have 

large safety margins when they do so. The pipe has to have rugged outside protection 

because it cannot be guaranteed that there will not be any debris, stones or fragments 

in the zone where the pipeline is situated. It is important for the traction head to be able 

to be fitted and removed quickly and straightforwardly when it is being recovered, even 

when the weather is very bad. The pipe and its joints have to be long-lived and resistant 

to tree roots. Because the paths followed by many pipelines are not exactly straight, it is 

vital for the sockets to be able to accommodate angular deflections. In inner-city areas, 

launch pits are a maximum of 7 metres in length so the ratio between the size of the 

launch pit and the number of joints to be made is very good. Because a combination of 

trenchless and open-trench techniques is often used, the types of pipe used have to be 

compatible and there has to be a complete range of fittings available, including for use in 

the intermediate pits. 

<strong>Buderus</strong> ductile cast iron pipes with cement mortar coatings and BLS ® joints have all 

these essential prerequisites. They are thus the ideal pipes for the trenchless replacement 

of pipelines. What is more, there are fittings for performing leak tests which are very 

easy to use and which are easily fitted and removed. The requirements in respect of 

permitted tractive forces, angular deflections and minimum radiuses of curves which 

have to be met under the DVGW rules and the internal rules of Berliner Wasserbetriebe 

are given in Tables 2.1 and 2.2 in section 2. 

When the technique is being used in sandy soils, the external shape of the socket, with its 

shoulder-like transition to the main body of the pipe, has been found to be very successful. 

Where, in soils containing non-cohesive material, there is a transition to material of this 

kind individual pebbles tend to roll under the main body of the pipe during the pulling-in 

process, and the entire pipe string thus undergoes an upward movement as it is pulled 

in. The result may be excessively thin cover over the pipe and even pushing-up of the 

pavement at the surface. For special cases 

of this kind, <strong>Buderus</strong> has developed the 

ZMU-PLUS pipe on which the transition 

between the main body and the socket 

is filled in with additional layers of the 

cement mortar coating so that the upward 

movement described above will not occur 

(Figs. 3.1 and 3.17). 

2 

Fig. 3.16 A stack of DN 300 ZMU-PLUS pipes

3.4 Requirements for the site 

Requirements for the new pipe 

It goes without saying that when trenchless installation techniques are being, exacting 

demands are made not only on the pipes and the accessories but also on the machinery 

used by the companies doing the work and on their qualified specialist personnel. 

There has to be sophisticated quality assurance system in this case to ensure a high 

standard of safety and quality for the new pipeline. The company provides evidence 

that it is suitably qualified by having the appropriate certification under DVGW Arbeitsblatt 

GW 301 [3. ] in supplementary group GN 1. This ensures that the pipeline which 

is installed by trenchless means will meet the demands that are made on it not only 

from the point of view of cost of installation but also in the long term, even beyond the 

full operating life that is demanded. For a deposit, <strong>Buderus</strong> Giesserei Wetzlar GmbH 

will supply traction heads, which can also be used for other trenchless installation 

techniques, on hire. There are now a wide variety of variant traction heads which can 

be obtained through machinery suppliers. 

Fig. 3.17 ZMU-PLUS sockets and an inserting end 

3



[3.1] DVGW Arbeitsblatt GW 322-1: Grabenlose Auswechslung von 

Gas- und Wasserrohrleitungen – Teil 1: Press-/Ziehverfahren 

– Anforderungen, Gütesicherung und Prüfung) 

[Trenchless replacement of gas and water pipelines – Part 1: Presspull 

method – Requirements, quality assurance and testing] 

[3.2] DVGW-Arbeitsblatt GW 322-2: Grabenlose Auswechslung 

von Gas- und Wasserrohrleitungen – Teil 2: Hilfsrohrverfahren 

– Anforderungen, Gütesicherung und Prüfung 

[Trenchless replacement of gas and water pipelines – Part 2: Auxiliary 

pipe method – Requirements, quality assurance and testing] 

[3.3] DIN EN : Rohre, Formstücke, Zubehörteile aus duktilem 

Gusseisen 

und ihre Verbindungen für Wasserleitungen – Anforderungen und 


[Ductile iron pipes, fittings, accessories and their joints for water 

pipelines – Requirements and test methods] 

[3. ] DVGW-Arbeitsblatt GW 301: Qualifikationskriterien für 

Rohrleitungsbauunternehmen 

[Qualification criteria for pipeline construction companies]

Reference documents

The burst lining technique 

4. The burst lining technique 

4.1 General 

The burst lining technique is used for the trenchless renovation of pipelines where the 

pipeline is to follow the same path. For this purpose, the existing old pipeline is destroyed 

by a bursting head and at the same time the fragments are pushed into the surrounding 

soil and the new run of pipe is pulled in. 

With burst lining, a distinction is made between the dynamic and static variants. 

In its dynamic form (Fig. .1), the burst lining technique was developed from the technique 

that uses a rocket plough with a widening head and was originally used for the 

renovation of stoneware sewer pipes. However, where adjacent lines and structures 

were too short a distance away, they were found to be at risk from the vibrations that 

were generated. 

Fig. 4.1 The dynamic variant of the burst lining technique 

This was why the static variant of the burst lining technique was subsequently developed. 

In this case a widening head (Fig. .2), the first widened part of which may be fitted with 

breaker ribs (Fig. .3), is pulled through the old pipeline by pulling units which operate 

continuously and without any vibration, and in this way the old pipeline is burst open. 

The new pipes are coupled straight to the bursting/widening head and are pulled into the 

bore, which is widened to approximately a 10% oversize.

Both the variants of the burst lining technique, both the static one and the dynamic 

one, are in practical use at the present moment and are widely used. The DVGW has 

catered for this fact with its Merkblatt GW 323 [ .3] and has thus established criteria 

for the execution of the techniques and also the related requirements and quality 

assurance measures. The burst lining technique is particularly well suited to old pipes 

made of brittle materials such as asbestos cement, stoneware and grey cast iron. However, 

by using the static variant and special cutting heads it is also possible for steel 

and ductile cast iron pipes to be burst. The new pipe which is pulled in may be of the 

same nominal size as the old pipe or, as dictated by the widening head which is used, 

of a larger size. (The widening head has to be at least the same size as the socket of 

the new pipe). 

Fig. 4.2 Widening head and cast iron pipe Fig. 4.3 Bursting head with breaker ribs 

General 

Another advantage that the burst lining of old pipes can be considered to have is that, 

compared with replacement in open trenches, there is none of the tricky work of handling 

the old pipes that there is in open trenches and none of the problems with safety at 

work which this causes. This is true whether replacement is to the same nominal size 

or a larger one. An increase in nominal size of up to two increments is possible. If the 

new pipeline can be smaller than the old one, an attractive alternative is pipe relining 

(see section 7). 

In the field of distribution systems, the use of the burst lining technique (or of any 

trenchless replacement technique) depends mainly on the number of intermediate pits 

required. Intermediate pits should be set up for house connections, fittings, changes of 

direction and cross-section and branch pipes. Bends up to 11° can usually be passed 

through. If there is too close a succession of house connections, open trench replacement 

may be more economical [ . ]. Equally important is the accuracy of the documentation 

on the existing old pipeline. If there are too many „surprises“ during the installation 

phase, the customer may find himself faced with a plethora of additional charges. 

7


4.2 A description of the technique 

As has already been mentioned, a distinction is made between the dynamic and static 

variants. In both, a bursting head is used to apply forces to the old pipeline which destroy 

it. Brittle materials are burst apart into fragments ( . ) and all the others are cut 

open (Fig. . ). The fragments or the cut-open parts of the pipe are pushed into the 

surrounding soil. 

Fig. 4.4 Fragments of grey cast iron Fig. 4.5 

An old pipe that was cut open under control 

4.2.1 The dynamic variant 

The force required for bursting is applied in the longitudinal direction of the pipe by a sort 

of soil rocket. This is driven by a compressor which is connected to it by a flexible hose. To 

guide the bursting head, it is pulled along by a winch from the arrival pit on a hook-equipped 

pulling rope which is pulled through the old pipe. The dynamic variant is particularly 

suitable for highly compacted and stony soils and for old pipes which are brittle. 

4.2.2 The static variant 

In this case the force is applied to the bursting head by a traction linkage which, starting 

from the arrival pit, runs from the pulling unit through the old pipeline to the bursting 

head (Fig. . ). 

8 

Fig. 4.6 The static 

variant

During the pulling process, the traction unit is supported against the wall of the arrival 

pit. Successive parts of the traction linkage are taken apart backwards. The static variant 

is well suited to homogeneous soils which can be displaced easily. 

Fig. 4.7 Perforating wheel for ductile materials Fig. 4.8 Roller cutting blade 

A description of the technique 

There has now also been practical experience of the replacement of ductile pipe materials 

(ductile cast iron and steel) with pipes of ductile cast iron. In this case the old pipes are 

cut open (Fig. . ) with special perforating and cutting wheels (Figs. .7 and .8) and are 

bent open by the widening head which follows sufficiently far to allow the new pipeline 

to be pulled in after the head. Trials of the use of this technique have been conducted up 

to a nominal size of DN 00 [ .1] 

Fig. 4.9 Traction head for pulling 

in two pipes in parallel 

There have also been isolated instances where combinations of ductile cast iron pipes 

for the water pipeline and a plastic pipe as an accompanying duct to protect cables have 

been pulled into a steel pipe which had been cut open (Fig. .9). 

9


4.3 Pipeline materials 

Because the soil conditions are generally unknown and above all because of the sharpedged 

fragments (Fig. . ) which most certainly occur with the burst lining technique, 

care should be taken to see that the pipeline material used is one which is not sensitive 

to factors of this kind. 

4.3.1 Outside protection 

The coating of plastic-modified cement mortar (ZMU) which is used on ductile cast iron 

pipes provides excellent protection against the risks which are mentioned above. The 

socket joint is fitted with a cement mortar protecting sleeve or a shrink-on sleeve and is 

protected by a sheet-metal cone (Fig. .10). 

Plastic pipes may only be used if they have a protective outer sheath. (Please note that 

the investigations described in GWF 3/2000 [ . ] clearly indicate that even this protective 

outer sheath does not always provide protection against damage to the pipe within 

it caused by point loads.) 

0 

Fig. 4.10 Ductile cast iron pipe with a BLS ® 

joint, cement mortar coating, shrink-on sleeve 

and sheet-metal cone

4.3.2 Joints 

As in virtually all trenchless installation techniques, so with the burst lining technique 

too, there are quite high forces which are applied to the joints between the pipes and 

to the bodies of the pipes. The obvious course is therefore to opt for the joint which, of 

all the current pipe materials, is the one which has the highest permitted tractive forces, 

namely the BLS ® restrained joint (see Fig. 2.19 on page 22). Where this is particularly 

important is in highly compacted and rocky soils because it is precisely in these that 

very high tractive forces may occur. The permitted tractive forces for the BLS ® joint 

can be seen from DVGW Arbeitsblatt GW 323 or from Table 2.1 on page 20. A rule 

that applies generally is that on-line measurements must be made and documented to 

ensure that the maximum permitted tractive forces are being observed. It must be remembered 

in this case that the permitted tractive forces have to be reduced for plastic 

pipes as a function of their temperature and of time. 

4.4 To sum up 

Ductile cast iron pipes with a cement mortar coating and BLS ® joints are outstanding 

well suited to the burst lining technique. The principal factors are the particularly high 

loads the BLS ® joint is able to carry and the extremely highly resistant cement mortar 

coating, which means that you can be sure of getting a pipeline which will be both safe 

and reliable in the long term. Table .1 shows a selection of pipelines that have already 

been installed by <strong>Buderus</strong> using the burst lining technique. 

Installations 

Nominal size 

DN 

Length 

[m] 

Year 

Erfurt 1 0 12 2001 

Gladenbach - 

1 0 700 200 

Erdhausen 

100 0 200 

Bad Laasphe 100 00 200 

200 00 2007 

Ober Rabenstein 2 0 3000 200 /07 

Zittau 200 00 2007 

Siegen 1 0 2 0 2007 

Pipeline materials 

Table 4.1 Excerpt from the list of reference installations made by the burst lining technique using 

<strong>Buderus</strong> Giesserei Wetzlar GmbH ductile cast iron pipes 

1



[ .1] Levacher, R. Erneuerungen einer Verbindungsleitung DN 00 zwischen zwei 

Wasserwerken im Berstlining- und Spülbohrverfahren 

[Renovations of a DN 00 connecting pipe between two waterworks by the 

burst lining and directional drilling methods] 

GUSSROHRTECHNIK 0 (200 ), p. 17 

[ .2] Klemm, K. und Rink, W.: Einbau duktiler Gussrohre DN 2 0 mit dem 

Berstlining-Verfahren in Nähe der Burg Rabenstein bei Chemnitz 

[Installation of DN 2 0 ductile cast iron pipes by the burst lining technique 

close to Rabenstein Castle near Chemnitz] 

GUSSROHRTECHNIK 1 (2007), p. 7 

[ .3] DVGW–Merkblatt GW 323, Grabenlose Erneuerung von Gas- und 

Wasserversorgungsleitungen durch Berstlining ; Anforderungen, 

Gütesicherung und Prüfung, Juli 200 

[Trenchless renovation of gas and water supply pipelines by the burst lining 

method; requirements, quality assurance and testing, July 200 ] 

[ . ] Emmerich, P. und Schmidt, R.: Erneuerung einer Ortsnetzleitung im 

Berstliningverfahren 

[Renovation of a pipeline in a local system by the burst lining method] 


[ . ] GWF Heft Wasser/Abwasser, 1 1. Jahrgang, Oldenburg Industrieverlag 

München, März 2000 – Punktbelastung an Kunststoffrohren von Uhl, 

Haizmann (FHW Oldenburg) 

[Point loading on plastic pipes by Uhl, 

Haizmann (Oldenburg School of Economics)] 

2


3

The horizontal directional drilling technique 

5. The horizontal directional drilling technique 

5.1 General 

Since the early 1990‘s, there has been a close relationship between the development 

of this technique and ductile cast iron pipes. Back in 1993, Nöh [ .1] conducted some 

exploratory tests in which 0 m long DN 1 0 pipelines with positive locking joints were 

installed and were then withdrawn again from the bore to allow the surface stresses 

which had occurred to be assessed. The excellent results provided the justification for 

a 2 x DN 1 0 double culvert pipe about 200 metres long which was pulled in under the 

river Mosel in 199 at Kinheim, partly through rocky subsoil. 

Fig. 5.1 Pre-assembled DN 500 pipeline 

Fig. 5.2 Arrival at the arrival pit

Fig. 5.3 Assembly of the string of DN 900 pipes in a floodable trench 

Fig. 5.4 The string of DN 900 pipes floating in 

the trench when flooded 

General 

After this satisfactory experience, development went ahead at a very rapid pace: In 199 

the pipes were of DN 00 size [ .2] (Figs. .1 and .2), in 2000 the bar was raised 

to DN 00 [ .3] and in 2003 DN 700 pipes were pulled in by the horizontal directional 

drilling technique in the Netherlands [ . ]. The current record – held by <strong>Buderus</strong> 

Giesserei Wetzlar GmbH pipes with BLS ® joints and ZMU – is approximately 00 metres 

of DN 900 pipes in Valencia in Spain (Figs. .3 to . ). 

In parallel with this the DVGW was developing technical rules for the technique, and 

these took the form of Arbeitsblatt GW 321 Steuerbare horizontale Spülbohrverfahren 

für Gas- und Wasserrohrleitungen – Anforderungen, Gütesicherung und Prüfung [Steerable 

horizontal directional drilling methods for gas and water pipelines – Requirements, 

quality assurance and testing], which was published in October 2003 [ . ]. 

Fig. 5.5 Beginning of the pulling-in with a barrel 

reamer ahead of the string of pipes



The steerable horizontal directional drilling technique (HDD), which will be referred 

to below simply as the directional drilling technique, is the most widely used trenchless 

technique for installing new pressure pipelines for gas and water supply. DVGW 

Arbeitsblatt GW 321 gives rules relating to requirements, quality assurance and testing 

for it to ensure that quality is properly assured. 

The sequence of operations in the directional drilling technique is generally divided into 

the following three successive steps: 

• a pilot bore 

• an upsized bore or bores 

• pulling-in 

5.2.1 The pilot bore 

This is the first step in producing a bore, running from the starting point to the arrival 

pit, into which the string of pipes can be pulled. The pilot bore is driven under steered 

control by a drilling head at the tip of a drilling string. Emerging at high pressure from 

the drilling head as it drives is an aqueous suspension of bentonite, the so-called drilling 

mud, which is pumped through the drilling string to the drilling head by the drilling 

machine. The drilling mud serves both to carry away the material which is cut away and 

to support the bore. There are different designs of drilling heads for all types of soil. In 

sandy soils, all that is generally needed for detaching and carrying away the cuttings are 

Fig. 5.6 Drilling head for the pilot bore

the outlet nozzles. In rocky soils, drilling heads fitted with roller chisels can be used. 

The pilot bore is steered by controlled rotation of the bevelled steering surface of the 

drilling head. This surface moves off-line and it can be forced to move off-line in the 

desired direction by rotating it (Fig. . ). 

The actual position of the drilling head is detected above the path of the bore by means 

of radio signals from a transmitter housed in the drilling head. Any deviations from the 

desired line are corrected by appropriate steered movements. Today, the accuracy of 

steering is so high that, after being driven for a length of more than 1000 metres, pilot 

bores can be made to arrive within a target area measuring only a square metre in size. 

Fig. 5.7 

The tool for the first stage of upsizing 

5.2.2 The upsized bore or bores 


Fig. 5. 8 

The tool for the second stage of upsizing 

If the pilot bore needs to be upsized, suitable tools are used to upsize it, in a number 

of stages, to a diameter suitable for the pulling-in of the medium-carrying pipe. For this 

purpose, an upsizing head is fitted to the pilot drilling linkage, the size and configuration 

of this head being governed by the particular soil conditions and the size of the 

pipe which is subsequently going to be pulled in (Figs. .7 and .8). The upsizing head 

is pulled through the bore while rotating continuously and in this way it enlarges the 

size of the pilot bore. The soil which is cut away is carried out with the drilling mud and 

this latter supports the bore at the same time. The upsizing process is repeated with 

increasingly large heads until the bore is of the desired inside diameter. 

7


5.2.3 Pulling-in 

Once the bore has reached its final diameter, the string of pipes can be pulled in. A 

reaming tool (Fig. .9), then a rotary joint that stops the string of pipes from turning 

with the reaming tool, and then a traction head matched to the pipes that are going to 

be pulled in (Fig. .10) are fitted to the drilling linkage which is still in the bore. The 

traction head is connected to the string of pipes by friction locking and positive locking. 

The length of the string of pipes depends on local conditions. When the site is very 

cramped for space, part-strings can be assembled or even single pipes can be installed. 

When this has to be done, the pulling-in process is stopped after whatever length of 

string is possible in the given case and another part-string is coupled on. Drilling mud is 

also pumped through the drilling linkage while the pulling-in is progressing. It emerges 

from the reaming tool and as it does so carries away the drillings and at the same time 

lessens the frictional forces. The forces which act on the new string of pipes when it is 

being pulled in have to be measured and a record has to be kept of them. 

Fig 5.9 Reaming tool 

8 

Fig. 5.10 DN 900-BLS ® traction head

5.3 General requirements 

Companies with which orders for directional drilling operations are placed must have 

the requisite qualifications. This is considered to be the case if the company holds a 

DVGW certificate under DVGW Arbeitsblatt GW 301 [ . ] or GW 302 [ .7] as the 

case may be, in the appropriate class GN 2. As well as this, a specialist supervisor who 

is qualified under DVGW Arbeitsblatt GW 329 [ .8} has to be appointed within the 

company. 

5.3.1 Pipes and joints 

The pipes and joints must be suitable for the stresses which the technique produces. 

The permitted tractive forces, radiuses of bends and angular deflections are specified 

in Appendix A to Arbeitsblatt GW 321 for the usual pipe materials, namely steel, cross 

linked polyethylene (PE-X), PE 100 and ductile cast iron (see also Table 2.2 in section 

2). Depending on the material, the pipes may have to be given suitable outside protection 

which will protect them against damage such for example as scoring. 

5.3.2 Ductile cast iron pipes 

General requirements 

Ductile cast iron pipes to DIN EN (for drinking water) or DIN EN 98 (for sewage) 

are particularly suitable for trenchless installation by the directional drilling technique. 

A first feature which can be mentioned as being of significance in this connection is the 

actual material of the pipes. Ductile cast iron has the ability to survive extreme loads 

unscathed. Hence there is also virtually no chance of the wall of the pipe suffering 

damage from objects lurking unseen within the ground. 

Another excellent feature is the outside protection. Ductile cast iron pipes for the 

directional drilling technique are provided with a five millimetre thick coating of plasticmodified 

cement mortar (ZMU) to DIN EN 1 2 [ .9]. This effectively prevents any 

damage to the body of the pipe and is suitable for soils of whatever aggressiveness 

(under DIN 30 7 -2 [ .10]). 

The third prerequisite for the use of ductile cast iron pipes for the HDD technique 

is the BLS ® restrained joint. The BLS ® restrained joint, which is a longitudinal forcefit 

joint and a positive locking joint combines functionality and easy, quick and secure 

assembly. Without any great effort, it can be assembled in a matter of minutes even 

under the most adverse conditions, such as ice and snow. In this way it cuts the amounts 

9


of time that are lost during the pulling-in process when single pipes or part-strings are 

being fitted together to an almost irreducible minimum. At the same time it has, under 

DVGW Arbeitsblatt GW 312, the highest permitted tractive forces of all the usual pipe 

materials which are used for installing pipelines. These permitted tractive forces can 

be used without being reduced in any way the moment the joint has been assembled. 

Cooling times or reductions in the tractive forces due to high pipe-wall temperatures 

or ambient temperatures or due to protracted pulling-in times are unknown when 

ductile cast iron pipes are being installed. The permitted tractive forces, operating 

pressures and angular deflections are given in Table 2.1 in section 2. For the maximum 

permitted tractive forces given in the table, the use of an (additional) high-pressure 

lock is laid down for nominal sizes from DN 80 to DN 2 0. The operating pressures 

and tractive forces shown are based on a wall thickness class of K9. Higher figures, 

both for operating pressure and also for tractive force, are possible by, for example, 

increasing the wall thickness class. If the angular deflections are ≤ 0.5° per joint, the 

figures quoted can be raised by a further 0 kN. Because of the angular deflections of 

up to ° which are possible at each joint, a very small radius of curvature of only 9 

metres can be achieved. 

With regard to protection for the joints, the following options are available: 

• a sleeve of heat-shrink material to DIN 3072 

• a sleeve of heat-shrink material to DIN 3072 plus a sheet-steel cone 

• a cement mortar protecting sleeve plus a sheet-steel cone. 

The crucial factor in deciding on the protection for the socket is the installation technique 

which has been selected. 

There are basically two variant procedures that can be followed in pulling in ductile cast 

iron pipes: 

1. pulling-in of a string or part strings of pipes 

2. pulling-in of individual pipes. 

A point in favour of the first variant, the pulling-in of a string of pipes, is that the string of 

pipes is first assembled from individual pipes and is then filled with water and pressure 

tested before being pulled into the bore which has now been completed. For a long 

time, this variant was even laid down by insurers because it was considered safest. During 

the pulling-in there is only a brief interruption in the traction to allow the traction 

rod to be removed at the machine end. The time this takes has to be kept as short as 

possible to stop the thixotropic effect from taking place in the drilling mud. This effect 

causes it to solidify. 

0

A prerequisite for this procedure is sufficient space for a complete pipe string, or partstrings 

situated next to one another, to be assembled. A disadvantage is the total weight 

of the pipe string, which increases the tractive forces required due to the friction of 

the string against the ground on which it is resting. This friction can be reduced by, for 

example, sheets of metal greased with lubricant on which the string is assembled or by 

inflated rubber rollers. If there are water-filled channels available, the string can float 

in them (Fig. . ). Generally speaking, it has to be said that the pulling-in of a complete 

string (Fig. .1) destroys the advantage of the point sites which are used in trenchless 

installation techniques. Basically, this is true no matter what the material of which the 

pipes are made. The pulling-in of single pipes is particulary suitable for point sites but 

normally cannot be used for pipes which have to be joined together into strings by 

welding because the time taken by the welding and cooling and by the testing of the 

welds is too long. The inevitable consequence is that the drilling mud solidifies due to 

thixotropy. 

Fig. 5.11 General diagram of an assembly pit 

7 - 8 m 

Allgemeine Anforderungen 

This is where the advantage of the BLS ® joint lies. The time taken to assemble the 

<strong>Buderus</strong> BLS ® joint is short and is similar to the time required to remove the traction 

rod at the machine end (see Table 2. in section 2). This gives ductile cast iron pipes 

with BLS ® joints an unbeatable lead over pipes of other materials, with the possible 

exception of PE pipes supplied in coils. The space required at the end from which the 

pipeline is pulled in is only slightly more than the length of a pipe. Launch pits seven to 

eight metres in length are generally all that are required (Fig. .11), or else the pipes 

are joined together on an assembly ramp. A point site is possible with these latter 

pipes. There are no forces generated by friction on the ground below which have to 

be allowed for and in general the next smaller size of machine can even be used, which 

1


is another thing which has beneficial 

effects on cost. The connecting together 

of single pipes on a ramp also has the 

advantage that the work can be done 

at eye level, virtually under workshop 

conditions, which is important from an 

ergonomic point of view (Fig. .12). 

Another inestimable advantage with 

regard to drinking water hygiene and the 

subsequent release that is required is that 

the assembly of the joints on a ramp takes 

place some distance away from any dirt 

and mud. 

2 

Fig. 5.12 Assembly ramp 

Fig. 5.13 cement mortar protecting sleeve with a sheet-metal cone 

It is clear that the gain in speed with the variant procedure described above must not 

be lost again by the application of a heat-shrink sleeve. This is where the cement mortar 

protecting sleeve serves its purpose. It can be quickly and easily rolled on and it has a 

sheet-metal cone to protect it against the unknown roughnesses which may be present 

in the bore. This cone is slid over the socket of the pipe, together with the cement mortar 

protecting sleeve, before the joint is assembled. Once the joint has been assembled, 

it is moved into position (Fig. .13) and folded in at the edge if required.

Table .1 provides an overview of the possible ways of protecting the joint with the 

different variant procedures: 

Table .1: Possible ways of protecting the joint 

General requirements 

Variant Outside protection Joint protection 

Pulling-in of single pipes ZMU 

Cement mortar protecting 

sleeve plus sheet-metal cone 

Pulling-in of pipe strings or 

part-strings 

ZMU 

Cement mortar protecting 

sleeve or shrink-on sleeve plus 

sheet-metal cone 1) 

1) Information on this subject can be found in our product catalogues. Shrink-on sleeves of 

tape material should be avoided on directionally drilled pipelines if at all possible. 

The two installation procedures mentioned above, namely the pulling-in of single pipes 

and the pulling-in of pre-assembled pipe strings or part-strings, are used as dictated by 

the amount of space available on site. In built-up inner city areas, it is, for the most part, 

the pulling-in of single pipes which has to be considered. A launch pit about seven to 

eight metres in length is required for this. Assembly and the protecting of the sockets 

take place in the pit. Interference with the surface of the street can be even smaller if 

the pipes are joined together on a mobile ramp. Depending on the governing conditions, 

such as nominal diameter, supporting ground and the preparation of the sliding 

surface of the pipe string, lengths of some hundreds of metres can be pulled in. 

Example: 

DN 200 ductile cast iron pipes with cement mortar coating, BLS ® joints and highpressure 

locks, wall thickness class K9 

• permitted tractive force F zul : 3 0 kN (PFA bar) 

• weight of pipe G pipe : 271,5 kg = 45,25 kg/m ≈ 0,46 kN/m 

• coefficient of friction µ = 1,0 

What is thus obtained for the permitted length of the pipe string, from the formula 

L perm = F perm / (G pipe * µ) = 350 kN / (0,46 kN/m * 1,0) ≥ 7 0 m 

In many cases, the coefficient of friction µ that will occur will be appreciably less than 

1.0, thus enabling substantially longer lengths to be installed. In this way, coefficients of 

friction of between 0. and 1.0 were found in a series of measurements of tractive 

force made on DN 00 pipes and the average was µ = 0.78 [ .11] 

3


5.4 To sum up 

In their current form, <strong>Buderus</strong> Giesserei Wetzlar GmbH‘s ductile cast iron pipes with 

coatings of plastic-modified cement mortar and BLS ® restrained joints are not only suitable 

for laying in open trenches but are also a useful alternative when modern trenchless 

installation techniques, such as steerable horizontal direction drilling, are being used. 

They combine a very simple joint system which can be assembled quickly and under 

almost any conditions but is still able to carry high loads with a coating which is equal to 

the demands made on it. What is more, the pipes will withstand virtually all the external 

stresses that occur in directional drilling and their material has what is by far the longest 

technical operating life of all pipe materials under DVGW Hinweis W 01 [ .12]. 

Ductile cast iron pipes are the right choice when it is a matter of making a lastingly 

worthwhile capital investment. Word has spread that this is the case, and proof of this 

can be seen in the many pipelines that have been installed in recent years and decades 

using the horizontal directional drilling technique. The list of reference installations given 

in Table .2 can only show a small number of the most interesting of these directional 

drilling projects.

Installations 

Nominal size 

DN 

length 

[m] 

Year 

Valencia, Spanien 900 0 2007 

Blankenfelde Mahlow, Kreuzung L 0 300 90 200 

Schwante, Dorfstraße 300 192 200 

Nieder Neuendorf, Düker Havelkanal 200 3 0 200 

Wolfenbüttel 00 2 200 

Halle, Maxim-Gorki-Straße 1 0 28 200 

Rügen, Prora 3. BA 

300 

2 0 

List of reference installations 

Table .2: List of reference installations on <strong>Buderus</strong> Giesserei Wetzlar GmbH‘s most 

important HDD projects 

Großbeeren, Kleinbeerener Straße 300 12 200 

Nieder Neuendorf, 1 BA 200 3 200 

Eichwalde 300 12 200 

Berlin Frohnau 100 78 200 

Münster bei Dieburg 100 90 200 

Dieburg, Groß-Umstädterstr. 1 0 208. 200 

Pegau 300 300 1998 

Schönebeck, Abwasserdruckleitung 00 220 1997 

Rostock 00 180 1997 

Wutha 00 0 1997 

Henningsdorf 00 22 199 

Oranienburg 00 32 

180 

1 

199 

Frankfurt am Main 100 

90 

80 

70 

100 

199 

Offenbach 100 

270 

280 

199 

Kinheim, Moseldüker 1 0 2 x 172 199 

This list of reference installations shows only a few of the installations which have been 

made by directional drilling using ductile cast iron pipes and is intended to provide an overview 

of the opportunities which exist and of the wealth of experience that we have had 

with installation work of this kind. 

2 

0 

200



[ .1] Nöh, H.: Moseldüker Kinheim, grabenloser Einbau von Gussrohrleitungen 

mit der FlowTex-Großbohrtechnik 

[Kinheim culvert under the Mosel. Trenchless installation of cast iron 

pipelines by the FlowTex large-bore drilling technique] 

GUSSROHRTECHNIK 30 (199 ) p. 2 

[ .2] Hofmann, U. u. Langner, T.: Einziehen eines 32 m langen Rohrstranges 

DN 00 mit gesteuerter Horizontalbohrtechnik – ein wichtiger Beitrag zum 

Umweltschutz in Oranienburg an der Havel 

[Pulling in of a 32 m long DN 00 pipe string by the steered horizontal 

directional drilling technique – An important aid to environmental protection 

in Oranienburg on the Havel] 

GUSSROHRTECHNIK 32 (1997) p. 

[ .3] Fitzthum, U.; Jung, M. u. Landrichter, W.: Eine Baumaßnahme der 

besonderen Art: 1100 m Leitungsbau mit duktilen Gussrohren DN 00 blieb 

von den Anliegern in Fürth unbemerkt 

[A special kind of construction project: local residents did not notice the 

installation of a 1100 m long pipeline of DN 00 ductile cast iron pipes] 

GUSSROHRTECHNIK 3 (2000) p. 33 

[ . ] Renz, M.: Rekordpremiere mit duktilen Gussrohren DN 700 im 

Spülbohrverfahren in den Niederlanden 

[A record first for DN 700 ductile cast iron pipes installed by the directional 

drilling technique in the Netherlands] 

GUSSROHRTECHNIK 37 (2003) p. 3 

[ . ] DVGW Arbeitsblatt GW 321: Steuerbare horizontale Spülbohrverfahren für 

Gas- und Wasserrohrleitungen – Anforderungen, Gütesicherung und Prüfung, 

Okt. 2003 


– Requirements, quality assurance and testing]


[ . ] DVGW Arbeitsblatt GW 301: Qualifikationskriterien für 

Rohrleitungsbauunternehmen Juli 1999 

[Qualification criteria for pipeline construction companies, July 1999] 

[ .7] DVGW Arbeitsblatt GW 302: Qualifikationskriterien an Unternehmen für 

grabenlose Neulegung und Rehabilitation von nicht in Betrieb befindlichen 

Rohrleitungen, Sept. 2001 

[Qualification criteria to be met by companies for the trenchless relaying and 

rehabilitation of out-of-service pipelines, Sept 2001] 

[ .8] DVGW Arbeitsblatt GW 329: Fachaufsicht und Fachpersonal für steuerbare 

horizontale Spülbohrverfahren; Lehr- und Prüfplan, Mai 2003 

[Specialist supervisors and specialist personnel for steerable horizontal 

direction drilling methods; plan for instruction and testing, May 2003] 

[ .9] DIN EN 1 2: Rohre, Formstücke und Zubehör aus duktilem Gusseisen – 

Zementmörtelumhüllung von Rohren – Anforderungen und Prüfverfahren, 

Sept. 200 

[Ductile iron pipes, fittings and accessories – External cement mortar coating 

for pipes – Requirements and test methods] 

[ .10] DIN 30 7 -2: Äußerer Korrosionsschutz von erdverlegten Rohrleitungen; 

Schutzmaßnahmen und Einsatzbereiche bei Rohrleitungen aus duktilem 

Gusseisen., April 1993 

[External corrosion protection of buried pipes; corrosion protection systems 

for ductile iron pipes, April 1993] 

[ .11] Renz, M.: Premiere des Spülbohrverfahrens mit duktilen Gussrohren DN 00 

bei Einzelmontage in den Niederlanden 

(A first for the directional drilling technique using individually assembled 

DN 700 ductile cast iron pipes in the Netherlands] 

GUSSROHRTECHNIK 0 (200 ) p. 13 

[ .12] DVGW Hinweis W 01: Entscheidungshilfen für Rehabilitation von 

Wasserrohrnetzen 

[Aids to decision-making for the rehabilitation of water-pipe systems] 

7

The rocket plough technique 

6. Installing ductile cast iron pipes by the 

rocket plough technique 

6.1 General 

For quite some time now, it has been the practice in rural areas for cables and plastic 

pipelines to be ploughed in from a drum provided there was no existing infrastructure 

or other obstacles along the path of the run. Where this is preferably done is along 

farm roads at the edges of areas used for agricultural purposes. The technique was 

successfully tried out for the first time using ductile cast iron pipes in 2000, as part of 

a research project, and it has now developed into a standard technique which has now 

been covered in the sets of rules issued by the DVGW and DWA. What is used for the 

installation of ductile cast iron pipes is the trailing plough procedure detailed in ATV 

DVWK Merkblatt M 1 0 [ .1] and DVGW Arbeitsblatt GW 32 (draft of /0 ) [ .2]. 


A cavity is produced by a widening body shaped like the nose of a rocket at the bottom 

end of a ploughshare. A pipe string, which is attached to the widening body, is pulled 

into this cavity in the same stage of the operation. Fig. .1 shows the principle of the 

technique. So far it has been used with pipes of nominal sizes from DN 80 to DN 300. 

The machinery required consists of the traction vehicle (Fig. .2) and a plough (Fig. .3) 

carrying a ploughshare. To ensure that the vertical position of the path followed by the 

run remains constant when the profile of the terrain varies, the depth of penetration of 

the share can be controlled hydraulically. 

Fig. 6.1 The rocket plough technique 

8 

Launch 

pit 

Pipe string with 

traction-resistant joints 

Warning strip 

Widening 

body 

Ploughshare 

Rocket plough Traction vehicle 

Pilling 

rope 

Winch 

Support 

plate

Fig. 6.2 Traction vehicle Fig. 6.3 Plough on low-loader Fig. 6.4 Traction vehicle 

and steel rope 

A steel rope (Fig. . ) connects the plough to the traction vehicle and the latter can be 

supported on the ground by means of a support plate, to enable the tractive forces to be 

transmitted into the ground. The string of ductile cast iron pipes, which is connected by 

longitudinal force-fit joints, is laid out along the line of the run. The string is then hooked 

onto the widening body (Fig. . ) and is ploughed into the earth (Fig. .7) from a launch 

pit with an inclined ramp (Fig. . ). The length of the launch pit depends on the angular 

deflection of which the longitudinal force-fit restrained joints are capable. 

Fig. 6.5 Ploughshare with widening body 

Fig. 6.6 Launch pit 


Fig. 6.7 Ploughing-in process 

9


6.3 Outside protection 

With the rocket plough technique, the outside protection of the pipes is a matter of particular 

importance because the string of pipes which is hooked on is generally ploughed 

into the existing soil without any lubricants (bentonite or the like). Because there is generally 

no exact knowledge of just what the conditions are in the subsoil, the pipes require 

an outside protection which is able to carry high loads and which will remain undamaged 

even when subjected to extreme mechanical stresses and will thus stay effective for the 

entire life of the pipeline. 

What is used for this purpose in the case of ductile cast iron pipes is a plastic-modified 

cement mortar coating (Fig. .8) to DIN EN 1 2 [ .3]. 

What is used to protect the socket joints is either polyethylene shrink-on material (Fig. 

.9) to DIN 30 72 [ . ], with an additional sheet-metal cone to provide the shrink-on 

material with mechanical protection during the pulling-in process, or a cement mortar 

protecting sleeve with a sheet-metal cone for mechanical protection 

Fig. 6.8 Plastic-modified 

cement mortar coating 

70 

Cement mortar 

lining 

Ductile cast iron 

Cement mortar 

coating 

Zinc coating 

Fig. 6.9 Joint protection 

Fig. 6.10 Sheet-metal cone

6.4 Joints 

The longitudinal force-fit BLS ® restrained joint (Fig. .11) is used for the rocket plough 

technique. Over the size range from DN 80 to DN 2 0, this BLS ® joint is supplemented 

by a high-pressure lock (Fig. .12) to enable the transmission of the tractive forces to be 

maximised. 

Fig. 6.11 BLS ® joint Fig. 6.12 Joint with a high-pressure lock 

6.5 Permitted tractive forces and minimum radiuses for curves 

The permitted tractive forces and the minimum radiuses for curves are given in DVGW 

Arbeitsblatt GW 32 (draft of /0 ) and in ATV Merkblatt ATV-DVWK-M 1 0 (Table 1) 

or can be seen from Table I in section 2. With regard to the design and construction of 

the components of the longitudinal force-fit joints, the VRS joint which is dealt with in 

the DVGW Arbeitsblatt and the ATV-DVWK Merkblatt corresponds in all respects to the 

BLS ® restrained joint. 

Fig. 6.13 BLS ® traction head 

Outside protection, joints, tractive forces, radiuses of curves 

Catch 

Left lock Right lock 

High-pressure 

lock 

71


6.6 Areas of application and advantages of the installation technique 

The rocket plough technique is particularly suitable for the installation of pipelines in rural 

areas and in areas where ground water and surface water is subject to statutory protection. 

Intersections with small, shallow bodies of surface water and installation in embankments 

do not present any problems for this installation technique. Installation below the water table 

is equally possible. The terrain must not be surfaced and must not contain any obstacles 

of any great size in the area through which the path of the pipeline runs. The exact position 

of any intersecting pipes or lines must be precisely known in advance. The rocket plough 

technique is very suitable for use in types of soil which can be easily displaced. Displaceable 

soils include unconsolidated deposits of mixtures of gravel and silt, mixtures of gravel and 

clay, mixtures of sand and silt and mixtures of sand and clay. 

Additional protective pipes, cables and warning strips can be installed at the same time 

as the pipeline is being pulled in (Fig. .1 ). A suspension of bentonite can be fed in to 

fill up the annular space or to reduce the frictional forces. Individual strings of pipes are 

connected together by means of collars (Figs. .1 and .1 ). 

Fig. 6.14 Pipeline, protective pipe and warning 

strip 

72 

Fig. 6.15 Connection between strings of pipes 

Fig. 6.16 Connection made with a collar Fig. 6.17 Surface of ground after the pulling-in

Areas of application, advantages and reference installations 

The disturbed soil that is left on the surface after the pipeline has been pulled in (Fig. 

.17) is smoothed down again with a digger. 

These are some other advantages of the rocket plough technique: 

• low installation costs compared with conventional techniques 

• short installation times 

• no removal of top-soil required 

• space required for making the run is not very wide (up to about six metres) 

• there is no mixing of soils 

• depths of installation of up to two metres. 

A feature which needs to be stressed is the speed of installation which can be achieved: 

it is generally between two and seven metres a minute. 

Table .1 shows some of the pipeline installation projects which have been carried out in 

recent years with the rocket plough technique. 

Table .1: Excerpt from the list of reference installations entitled „Ploughing-in of ductile 

cast iron pipes“ 

No. Location Nominal Size Length 

1 Laue-Poßdorf (near Delitzsch) 200 1.2 8 m 

2 Impfingen 1 0 797 m 

3 Hergenstadt 1 0 2. 00 m 

Untersollbach 1 0 2.037 m 

73



[ .1] DVGW Arbeitsblatt GW 32 (Entwurf /0 ) – Fräs- und Pflugverfahren für 

Gas- und Wasserrohrleitungen; Anforderungen, Gütesicherung und Prüfung 

[Cutting and ploughing techniques for gas and water pipelines; requirements, 

quality assurance and testing] 

[ .2] ATV-DVWK-Merkblatt M 1 0 Fräs- und Pflugverfahren für den Einbau von 

Abwasserleitungen und -kanälen, Oktober 2003 

[Cutting and ploughing techniques for the installation of sewage pipes and 

conduits, October 2003] 

[ .3] DIN EN 1 2: Rohre, Formstücke und Zubehör aus duktilem Gusseisen – 

Zementmörtelumhüllung von Rohren – Anforderungen und Prüfverfahren, 

Sept. 200 

[Ductile iron pipes, fittings and accessories – External cement mortar coating 

for pipes – Requirements and test methods] 

[ . ] DIN 30 72: Organische Umhüllungen für den Korrosionsschutz von in Böden 

und Wässern verlegten Rohrleitungen für Dauerbetriebstemperaturen bis 

0° C ohne kathodischen Korrosionsschutz – Bänder und schrumpfende 

Materialien, Dez. 2000 

[External organic coatings for the corrosion protection of buried and 

immersed pipelines for continuous operating temperatures up to 0°C 

– Tapes and shrinkable materials, Dec. 2000] 

7


7

The pipe relining technique 

7. Renovation of supply and drainage pipelines with ductile 

cast iron pipes by the relining technique 

7.1 General 

When pipelines are renovated by the relining technique, a new pipeline is pulled or 

pushed into an existing pipeline. This always results in a reduction in the hydraulic crosssection 

of the pipeline. When relining is carried out with ductile cast iron pipes, the 

reduction in the cross-section of the pipeline depends on the outside diameter of the 

sockets in the new pipeline. The pipeline suffers a loss of hydraulic performance. To 

some degree this is compensated for by the smooth interior surface of the new pipeline 

(the low roughness of its walls). Old pipelines are often encrusted on the inside and 

the roughness of their walls is therefore high. The relining technique can be used for 

drinking water pipelines, industrial water pipelines, pressure waste water pipelines and 

gravity waste water pipelines. 

In Germany, the consumption of drinking water by the population and by industry is 

going down. A reduction in the hydraulic cross-section of a pipeline is therefore often 

an advantage to the operator, because the rate of flow of the water is accelerated again 

and the dwell time of the water in the pipeline is shorter, by which means it is often 

possible for health problems to be avoided. 

With waste water pipelines too, the rate of flow goes up as a result of the relining, and 

in many cases this is a way of stopping the solids carried in the waste water from settling. 

Because of deposits of solids, waste water pipelines often have to be cleaned at 

relatively short intervals by high-pressure flushing or by using go-devils. 

Wherever there are pipelines where the intervals between changes of direction or 

lateral connections are not too short, renovation by the relining technique is always 

more economical than renovation by relaying in open trenches. This is true above all 

of runs of pipes below paved or metalled surfaces (e.g. surfaces carrying traffic) or in 

built-up areas. 

7

7. 2 A description of the technique 

In the relining technique, ductile cast iron pipes to DIN EN [7.1] or DIN EN 98 

[7.2] are pushed or pulled into the existing, old pipeline. They slide on their sockets 

when this is done. What is important in this case is for the old pipeline to be properly 

prepared. When work of this kind was done in the past, it was found that a coefficient 

of friction of µ < 1.0 can always be achieved if the old pipe is properly prepared – if encrustation 

is removed (Fig. 7.1), if gaps in the floor of the pipe at the sockets are closed 

off, if lubricant is applied to the floor of the pipe, and so on. 

Generally speaking, the annular space left between the old pipe and the new pipe is 

filled with an alkaline insulating material. If this is done, ductile iron pipes with zinc 

coating and cover coating are sufficient (Fig. 7.2). If not, ductile iron pipes with cement 

mortar coating have to be used. 

Fig. 7.1 High-pressure cleaning of the old 

pipeline 

7.2.1 Pulling-in 

For pulling-in, the positive locking longitudinal 

force-fit BLS ® restrained joint (Fig. 

7.3) needs to be used. 

Fig. 7.3 

Cut-away views of the DN 80 to DN 500 and 

DN 600 to DN 1000 BLS ® restrained joints 

A description of the technique, pulling-in 

Fig. 7.2 Insulation of the annular space 

77


The maximum tractive forces which are permitted in this case are taken from the type 

tests to DIN EN for movable longitudinal force-fit restrained joints. From the allowable 

component operating pressures PFA and PMA which were determined in these 

tests, the permitted tractive force is calculated using the formula P type = 1, x PFA + 

bar, decreased by a safety factor of S = 1.1. 

The worst-case incidental conditions were taken as a basis for the type testings. These 

were for example: 

• joint with largest annular space that is possible and subject to load at the crown 

• joint with largest annular space that is possible and at maximum angular deflection 

• 2 ,000 cycles of internal pressure varying cyclically between PMA and (PMA- ) 

The permitted tractive forces which were determined in this way are specified in 

DVGW Arbeitsblatt GW 321 [7.3], DVGW Arbeitsblatt GW 322 [7. ] and DVGW 

Merkblatt GW 323 [7. ]. 

The permitted tractive forces and the maximum possible angular deflections for the BLS ® 

restrained joint, and also the minimum radius which is possible for curves, can be found in 

Table 2.2 in section 2. Higher figures, both for operating pressure and for tractive force, 

are possible by, for example, increasing the wall thickness class. If the angular deflections at 

the sockets are ≤ 0.5°, then the figures given can be increased by a further 50 kN. 

It has proved successful for the new string of pipes to be pulled in with traction rods and 

a report on this appears in [7. ]. Pulling-in with a winch and steel rope is not recommended 

nor is the use of friction-locking longitudinal force-fit joints. A traction head 

is always required for pulling in the new string of pipes. This is produced from a BLS ® 

restrained joint (Fig. 7. ). 

Fig. 7.4 Representation of pipe plus traction 

linkage 

78 

Fig. 7.5 BLS ® traction head

<strong>Buderus</strong> Giesserei Wetzlar GmbH is able 

to make traction heads available to the 

companies doing the work on hire against 

a hire charge. At least two pits are always 

required for renovation by the relining 

technique. The size of the pits depends on 

the traction equipment that is used. The 

pipes are six metres in length and because 

of this the assembly pit should be at least 

eight metres long. The width of the assembly 

pit depends in the nominal size of pipe 

which is going to be installed (Fig. 7. ). 

7.2.2 Pushing-in 

Fig. 7.6 View of an assembly pit 

For pushing-in, ductile cast iron pipes having TYTON ® restrained joints which are not 

of the longitudinal force-fit type are pushed into the old pipeline. When this is done, 

the axial thrust is transmitted to the end-wall of the TYTON ® socket from the endface 

of the inserting end. Because the inserting ends of the pipes are bevelled, it is not 

the entire cross-section of the pipe-wall that is available to transmit the axial thrust 

(Fig. 7.7). Also, allowance must be made under DIN EN for the smallest outside 

diameter that is possible for the pipes. 

The compressive strength of ductile cast iron is σ D = 0 N/mm². 

Leaving aside any safety factor, a pressing force of P = σ D x A wall is thus possible, where 

A wall is the cross-sectional area of the wall of the cast iron which transmits the force. 

Fig. 7.7 Transmission of force in pushing-in 

P = σ D x A Wall 


79


However, the figures obtained by adopting this theoretical approach cannot under any 

circumstances be taken as permitted pushing-in forces. In view of the incidental conditions 

which may apply in the given case, such as possible angular deflections of the 

joints, the roughness of the wall of the pipe which is to be renovated, the annular gap 

which is left, and so on, it may be necessary to allow a considerable safety factor. 

Table 7.1 Calculation of theoretical pushing-in forces 

80 

DN d 1 

[mm] 

Wall thickness 

class 

s min 

[mm] 

Perm.σ = 

[N/mm 2 ] 

F perm 

[kN] 

80 98 K 10 .7 0 2 

100 118 K 10 .7 0 32 

12 1 K 9 .7 0 00 

1 0 170 K 9 .7 0 77 

200 222 K 9 .8 0 

2 0 27 K 9 .2 0 1010 

300 32 K 9 . 0 1 2 

3 0 378 K 9 0 1913 

00 29 K 9 . 0 2 

00 32 K 9 7.2 0 3787 

00 3 K 9 8 0 21 

700 738 K 9 8.8 0 3 99 

800 8 2 K 9 9. 0 1 1 

900 9 K 9 10. 0 70 0 

1000 10 8 K 9 11.2 0 92 2 

The pushing-in forces which are shown do not include a safety factor. This must be 

suited to the local conditions and must be agreed with the Applications Engineering 

Division of <strong>Buderus</strong> Giesserei Wetzlar GmbH. 

Example: DN 900, wall thickness K 9, A wall = 12.83 mm² 

Pressing force with no safety factor allowed for 

P = σ D • A wall = 0 N/mm² x 12.83 mm² = 70 0 kN 

With an assumed length for the pipe string of 200 m, DN 900 and wall thickness K 9, the 

weight of the pipe string would be ,000 kg ( t). With a coefficient of friction µ = 

1.0 a pressing force of 0 kN would be required. The theoretical maximum permitted 

pressing force F perm on the other hand is 70 0 kN (see Table 7.1).

Fig. 7.8 Pushing in a pipe 


Reports on relining work carried out using this technique appear in [7.7] and [7.8]. 

At the present time, no permitted pushing-in forces for ductile cast iron pipes are laid 

down in the existing sets of rules. The appropriate DVGW-Arbeitsblatt GW 320-1 currently 

exists as a draft. If there is an application, we always recommend consulting our 

Applications Engineering Division so that the pressing force which is permissible in the 

given case can be determined. When pipes are being pushed in, it is always the inserting 

end which leads and which is pushed into the socket of the pipe that was pushed in previously. 

The inserting end of the first pipe which is pushed in has to be fitted with a centring 

head. This can be made available on hire by <strong>Buderus</strong> Giesserei Wetzlar GmbH. 

As with pulling-in, at least two pits are 

required. The size of the pushing and assembly 

pit depends on the length of the 

pipes (which is usually six metres), on the 

pushing equipment used and on the nominal 

size of the pipes that are going to be installed. 

The size of the arrival pit depends 

on the nominal size and any other fitments 

which there may be. Fig. 7.9 Centering head with skids for sliding 

81



If the annular space left between the old 

pipe and the new one is filled with an alkaline 

insulating material, all that the pipes 

require is the outside protection consisting 

of a zinc coating with a cover coating. 

The sockets do not require any mechanical 

protection for pulling-in or pushing-in. 

If the annular space which is left is not 

filled, we recommend the use of pipes 

with a cement mortar coating (ZMU) to 

DIN 1 2 [7.9]. The restrained joints 

are protected by cement mortar protecting 

sleeves of rubber or shrink-on polyethylene 

material to DIN 30 72 [7.10]. 

The restrained joints are also given additional mechanical protection when being pulled 

in or pushed in (Fig. 7.10). 

7.4 Advantages of ductile cast iron pipes 

Ductile cast iron pipes are capable of carrying high loads. This ensures that all the forces 

which act on the pipeline both from inside and outside can be withstood without any 

problems just as they would be by a new pipeline that was laid in an open trench. The 

conditions, behaviour and steadiness of the old pipeline do not affect this. This is not 

something that is always ensured with plastic pipes. 

The economic advantage comes from the TYTON ® restrained joint, which is quick and 

safe to assemble. Depending on the nature of the pipe and its nominal size, with steel 

pipes the joints have to be welded in most cases, as they also do with plastic pipes. This 

is usually very time-consuming. While the welding is being done, the rest of the site personnel 

have to take a break and all the machines and other equipment are standing idle. 

Another point that <strong>Buderus</strong> ductile cast iron pipes have in their favour is their long 

technical operating life. 

82 

Fig. 7.10 Ductile cast iron pipe with ZMU, 

shrink-on sleeve and sheet-metal cone

7.5 Reference installations 

No. Location Year Old pipe New pipe Length Procedure 

1 

2 

3 

Berlin, 

Togostraße 

Berlin, B 101 

State border 

Berlin, 

Berliner Allee 

Leipzig 

Mölkau 

Leipzig, 

long-distance 

pipeline 

Thallwitz 

FWV Elbaue- 

Ostharz Güsten 

2003 

200 

200 

200 

200 

200 

Outside protection, Advantages, Reference installations 

DN 1000 

asbestos 

cement 

Doppelleitung- 

2x DN 

1000, grey 

cast iron & 

steel 

DN 1000 

steel 

DN 1100 

grey cast iron 

DN 1100 

grey cast iron 

DN 1000 StB 

steel 

DN 800 

ductile cast 


2x DN 800 

ductile cast 


DN 800 

ductile cast 


DN 900 

ductile cast 


DN 900 

ductile cast 


DN 800 

ductile cast 


1 0 Pulling-in 

2x 1100 Pushing-in 

300 Pushing-in 

372 Pushing-in 

3 Pushing-in 

7 2 Pulling-in 

83



[7.1] DIN EN 


ihre Verbindungen für Wasserleitungen – Anforderungen und 


[Ductile iron pipes, fittings, accessories and their joints for water pipelines 

– Requirements and test methods] 

[7.2] DIN EN 98 


ihre Verbindungen für die Abwasser-Entsorgung 

Anforderungen und Prüfverfahren 

[Ductile iron pipes, fittings, accessories and their joints for sewerage 

applications – Requirements and test methods] 

[7.3] DVGW-Arbeitsblatt GW 321 

Steuerbare horizontale Spülbohrverfahren für Gas- und Wasserrohrleitungen 

– Anforderungen, Gütesicherung und Prüfung 


– Requirements, quality assurance and testing] 

[7. ] DVGW-Arbeitsblatt GW 322-1 

Grabenlose Auswechselung von Gas- und Wasserleitungen – 

Teil 1: Press/Ziehverfahren – Anforderungen, Gütesicherung 

und Prüfung 

[Trenchless replacement of gas and water pipelines - Part 1: 

Press-pull method – Requirements, quality assurance and testing] 

[7. ] DVGW-Merkblatt GW 323 

Grabenlose Erneuerung von Gas- und Wasserversorgungsleitungen durch 

Berstlining; Anforderungen, Gütesicherung und Prüfung 

[Trenchless renovation of gas and water supply pipelines by the burst lining 

method; requirements, quality assurance and testing] 

8

[7. ] Rink, W.: 

Langrohrrelining mit duktilen Gussrohren DN 800 

[Pipe relining with DN 800 ductile cast iron pipes] 


[7.7] Schnitzer, G.; Simon, H. und Rink, W.: 

Langrohrrelining DN 900 in Leipzig – Mölkau 

[DN 800 pipe relining in Leipzig – Mölkau] 



[7.8] Bauer, A.; Simon, H. und Rink, W.: 

Sanierung der Thallwitzer-Fernleitung DN 1100 mit 

Langrohrrelining DN 900 

[Renovation of the Thallwitz DN 1100 long-distance pipeline by DN 900 

pipe relining] 


[7.9] prEN 1 2: Rohre, Formstücke und Zubehör aus duktilem 

Gusseisen – Zementmörtelumhüllung von Rohren – Anforderungen 

und Prüfverfahren, Sept. 200 

[Ductile iron pipes, fittings and accessories – External cement mortar 

coating for pipes – Requirements and test methods, Sept. 200 ] 

[7.10] DIN 30 72: Organische Umhüllungen für den 

Korrosionsschutz von in Böden und Wässern verlegten 

Rohrleitungen für Dauerbetriebstemperaturen bis 0° C ohne 

kathodischen Korrosionsschutz – Bänder und schrumpfende 

Materialien, Dez. 2000 

[External organic coatings for the corrosion protection of buried and 

immersed pipelines for continuous operating temperatures up to 0°C – 

Tapes and shrinkable materials, Dec. 2000] 

[7.11] DVGW- Arbeitsblatt GW 320-1 (Entwurf) 

Erneuerung von Gas- und Wasserrohrleitungen durch Rohreinzug mit 

Ringraum 

[Renovation of gas and water pipelines by pulling-in with annular space] 

8

8. Installation with steered pilot bore 

An interesting variant technique for the trenchless installation of new ductile cast iron 

pipelines was seen for the first time in 200 at the Berlin Water Exhibition [8.1]: a steered 

pilot bore was run to the arrival pit over a distance of approximately 70 metres using a 

tunnelling machine for microtunneling. As a second step, this pilot bore was upsized to a 

diameter of 80 millimetres by soil removal through auxiliary pipes containing an auger 

feeder. The third step was to withdraw the auxiliary pipes while at the same time pulling 

in individual ductile cast iron pipes. The accuracy which can be achieved with this variant 

technique is so great that even the stringent requirements of draft DWA Arbeitsblatt A 

12 [8.2] for gravity pipes can be met. 


The first step is to make the pilot bore. Starting from the launch pit, the pilot pipe is 

pressed through the displaceable soil to the arrival pit. An optical system, a steering 

head, a theodolite fitted with a CCD camera and a display are used to enable the target 

point to be homed in on exactly while direction and inclination are constantly monitored 

(Fig. 8.1). 

Fig 8.1 Step 1: Pilot bore 

8 

The steered pilot bore technique 

8.1 General 

1. Pilot bore 

Bohrtec 

BM 00 

Launch pit 

Surface of ground 

Drive of pilot bore 

Arrival pit

In the second step, the pilot is upsized by 

pressing in protective steel casing pipes 

with an outside diameter of 20 millimetres 

(Fig. 8.2). Together with the steel casing 

pipes, the lengths of pipe in the pilot 

bore are pushed to the arrival pit, disconnected 

there and recovered. The soil that 

is dug out as the bore is upsized is fed back 

to the launch pit by a feed auger which is in 

one metre long sections. In the launch pit 

the soil is collected in a bin, raised to the 

surface with the site hoist and collected in 

containers to be taken away (Fig. 8.3) 

2. Pressing in the casing pipe 

Bohrtec 

BM 00 

Launch pit 

Excavated soil Feed auger 

Fig. 8.3 Step 2: Pressing in the casing pipe 


20 mm dia. casing pipe 

plus hoses for betonite 


Fig. 8.2 Lowering the casing pipe 

Arrival pit 

87


In the third step of the operation, the first DN 300 ductile cast iron pipe for medium 

with BLS ® joints is lowered into the arrival pit (Fig. 8. ) and coupled to the traction head 

on the front casing pipe. The casing pipes, which are connected by longitudinal force-fit 

joints, are now pulled back to the launch pit; there they are recovered together with 

the feed auger. It takes next to no time for all the other pipes for medium to be coupled 

onto the pipe that has already been pulled in (Figs. 8. and 8. ). The traction head carries 

equipment for measuring the tractive force; this is used to measure the pulling-in forces 

acting on the string of pipes and, later on, to document them in a print-out. 

Fig. 8.4 Step 3: Pulling-in of the pipes for medium 

88 

2. Pressing in the casing pipe 

Bohrtec 

BM 00 

Launch pit 


20 mm dia. casing pipe 

Traction head & 

equipment for measuring 

tractive force 

Fig. 8.5 Lowering a pipe into the arrival pit 

DN 300 

ductile cast 

iron pipes 

The casing pipes and pipes for medium must be fitted with longitudinal force-fit joints 

Fig. 8.6 Coupling on a fresh pipe 

Arrival pit


Outside protection, joints, other points 

With this technique, the outside protection of the ductile cast iron pipes consists of 

plastic-modified cement mortar (ZMU) to DIN EN 1 2. The joint area has to be 

protected with a shrink-on sleeve. Shrink-on sleeves of tape material should not be used 

in this case. 

8.4 Joints 

Because the pipe for medium is pulled in by steered pilot boring, BLS ® joint also has to 

be used in this case. The permitted tractive forces and operating pressures for the BLS ® 

joint are shown in Table 2.1 in section 2. However, due to the oversize, the tractive 

forces which can be expected will not be excessively high. 

8.5 Other points 

The individual sections of the pipeline can 

be connected together in the conventional 

way in the assembly pits (which were 

previously the arrival and pull-in pits) using 

standard fittings. For pipelines connected 

entirely by longitudinal force-fit 

joints, BLS ® collars conforming to a factory 

standard are available (Fig. 8.7). For 

pressure tests, the sections are sealed 

off with thrust-locked fittings from the 

BLS ® range (Fig. 8.8, 8.9 and 8.10). There 

is thus no need for the end pieces to be 

supported on the pit lining. At 20 millimetres, 

the outside diameter of the casing 

pipe is so adjusted that there is a small 

oversize for the 20 millimetre sockets of 

the cast iron pipes. The outside diameter 

of the main body of the cast iron pipes, 

including the cement mortar coating, is 

approx. 33 millimetres. 

Fig. 8.7 BLS ® collar 

Fig. 8.8 BLS ® flanged socket 

89


The approximately 0 mm wide annular 

gap which this leaves fills up on its own if 

the soil is of a suitable type. So far, there 

have not been adverse effects on the 

ground surface due to settling. 

The technique is fully developed in technical 

terms. It combines the well known 

steered pilot boring technique which has 

proved its worth in the field of sewage 

pipe installation with the technique of pulling 

in ductile cast iron pipes with longitudinal 

force-fit restrained joints. There is only 

a small amount of interference with traffic 

and the environment. This technique 

is proving to be very economical and the 

reasons for this are the short installation 

times, the saving on below-ground work, 

such for example as the lining of pipe 

trenches, the temporary storage of soil, 

and transport to and from the site, the 

kindliness to any adjacent infrastructure, 

and the low-emission nature of the installation 

work. 

90 

Fig. 8.9 BLS ® flanged spigot 

Fig. 8.10 BLS ® plug


[8.1] Richter, D. und Rau, L.: Grabenloser Einbau von Druckrohren 

DN 300 im Einzug nach gesteuerter Pilotbohrung 

[Trenchless installation of DN 300 pressure pipes by pulling-in after a steered 

pilot bore] 


[8.2] DWA Arbeitsblatt – A 12 Rohrvortrieb, 09/9 

[Pipe driving, 09.9 ] 


91

A consideration of the economics of trenchless techniques 

9. A consideration of the economics of trenchless techniques 

The view generally held today is that a technique for installing pipes can be considered 

economical when the pipeline to be installed with it can be tendered for and installed at 

the lowest price. If this is the view that is adopted, then it will be only very rarely that 

the costs of operating and maintaining the pipeline are considered, let alone the costs of 

replacing it at the end of its normal operating life. 

§ 21, no. 2 of Part A of the German Regulations relating to the Placing of Contracts for 

Construction Services (the VOB/A) demands that tenders be checked from an economic 

point of view. Even today, there are specialist commentaries that put an interpretation 

on this demand, as follows: 

There is a close connection between the checking of tenders from an economic 

point of view and their consideration from a technical point of view. 

Whether a price is reasonable is determined by the best ratio between price and performance, 

including operating life, operating and maintenance costs, and any other 

costs which may arise at times close to or remote from the present. 

In § 2 , no. 3, paras. 2 and 3 of the VOB/A it is even stated that: 

„ … in assessing reasonableness, the economy of the method of construction, the 

technical solutions adopted or other favourable conditions of execution must be 

taken into account.“ 

„ … the contract is to be awarded to the tender which appears most economical 

in the light of all the relevant considerations, such for example as price, deadline 

for completion, operating and consequential costs, design, profitability or technical 

merit. The lowest tendered price alone is not the deciding factor.“ [9.1] 

Costs which have not generally been considered in the past are those which are caused 

by the work of installing or laying pipelines, in its surroundings, and which the general 

public have to acquiesce in paying, without any prospect of reimbursement, in the form 

of interference with traffic, noise nuisance and environmental pollution. This being so, 

it is almost impossible for any fair financial comparison to be made between the trenchless 

and open-trench techniques because the „social“ costs paid by the general public, 

though it may be perfectly possible to put a figure on them, are not taken into account 

when contracts are being placed. However, if the external incidental conditions make 

it difficult from the constructional point of view for a pipeline to be installed by the 

92


open-trench technique, then to an increasing degree there are better prospects for the 

trenchless techniques. The wide range of variant techniques which have today been 

developed to a high level of technical sophistication make it possible for a suitable and 

economical technique to be selected for every project. 

The operator‘s requirement for a network of drinking water pipes to be safe is reflected 

in DVGW Hinweis W 09 „Effects of the construction procedure and method on the 

economy of the operation and maintenance (on the network operating costs) of water 

distribution systems“ [9.2]. From the operating point of view, there are advantages in 

laying pipelines in open trenches; extensive and well-founded experience is available: 

Existing pipelines are visible and preset minimum spacings can be closely maintained. 

The pipeline can be installed, pressure-tested and measured out by „visual 

inspection“. 

Any adverse effects on the new pipe (e.g. from stones) can be almost ruled out. 

All the joints between pipes can be checked before the trenches are backfilled. 

Hydrants or connecting pipes can be installed at any later date. 

If pipes are damaged then, in the present state of the art, there are no restrictions on 

the locating of leaks. 

Planned requirements relating to high and low points and to lateral spacings can 

readily be satisfied by the construction work. 

Any damage to facilities belonging to third parties can be very largely ruled out. 

For trenchless techniques on the other hand, W 09 makes the proviso that, due to the 

fact that the renovated or rehabilitated pipeline will not be fully visible, there will have 

to be increased expenditure on monitoring of the installation work and on quality control. 

Nevertheless, experience is gradually showing that, generally speaking, trenchless 

installation and renovation techniques may be more economical than the conventional 

open-trench techniques if the regional competition for pipeline projects which are put 

out to tender is focussed on these techniques. Thus, one regional gas and water supply 

company has for example published a comparison between open-trench and trenchless 

construction as shown in Table 9.1. 

93


9 

Conventional construction Trenchless construction 

Length of pipeline 100% 100% 

Digging up of surface 100% 1 % 

Construction time 100% 30% 

Cost 100% 0 - 70% 

Operating life 100% 70 - 100% 

Kindliness to resources 20% 80% 

Noise, environment, 

adverse effects 

100% Intangible gain 

Table 9.1 

Overall comparison of open-trench construction with trenchless construction [9.1] 

A rough comparison of the costs of trenchless renovation techniques with those of the 

open-trench method likewise shows clear potential savings for the trenchless techniques 

(Table 9.2) 

Open-trench 

construction 

Bursting 

Rocket 

ploughing 

Trenchless construction 

Press-pull 

technique 

100% 70% 70% 80% 

With 

annular gap 

Relining 

Without 

annular gap 

Hoses 

0% 70% 0% 

Table 9.2: Rough comparison of the costs of the construction techniques [9.1] 

Quite a large project for conduit renovation which was carried out in Friedrichshafen by 

the burst lining technique gave a figure of 3 % for the reduction in costs compared to 

the conventional technique, and thus confirmed [9.3] the details given in [9.1]. Replacement 

in the same nominal size of 800 metres of DN 00 ductile cast iron pipes by the 

static burst lining technique has shown a cost saving of 22% [9. ]. The point at which the 

trenchless techniques cease to be economical is when the density of the house connections 

rises beyond a certain figure, because the cost of below-ground work and restoration 

of the surface then rises to a disproportionate extent [9. ]. 

To ensure the quality of drinking water pipelines which are renovated or installed trenchlessly, 

the DVGW has in recent years worked out comprehensive technical rules in the


form of the series of documents numbered GW 321 et seq. which ensure exactly that. 

The parameters of current trenchless installation and renovation techniques which are 

relevant to quality are described and laid down, together with limit values and directions 

for measuring them. 

DVGW Hinweis W 09 stresses the paramount influence which the pipe system selected 

has on the choice of the installation or renovation technique. The principal considerations 

affecting the choice of the pipe system are stated to be the following: 

1. Bedding conditions and conditions of use (e.g. diffusion characteristics, reserves of 

performance) 

2. Functionality of the corrosion protection systems and the connecting technology 

3. Whether experience has been good with the given system 

. Reasonable availability (delivery times, stocks held, continuity of systems). 

In what follows, the system consisting of ductile cast iron pipes with BLS joints and cement 

mortar coatings will be looked at more closely to see how well these four principal 

requirements are met. 

Requirement 1: 

Experience shows that ductile cast iron pipes are the pipes least sensitive to faults in 

the bedding. The disadvantage which trenchless techniques have that the bedding for 

the pipes cannot be checked is of least significance with pipes of this type, a fact which 

is proved not least by the excellent results shown by the DVGW‘s damage statistics for 

the water industry [9. ]. The non-diffusiveness of ductile cast iron pipes makes them 

preferable to plastic pipes in contaminated soils [9.7]. Because of their high energy of 

deformation, ductile cast iron pipes have the greatest reserves of performance, both in 

respect of static and dynamic loads from the internal pressure or the covering earth and 

in respect of the permitted tractive forces (see section 2). 


Given that the bedding and supporting conditions are unknown and uncheckable with 

trenchless installation techniques, it is ductile cast iron pipes with, usually, a cement 

mortar coating to DIN EN 1 2 that are used for these techniques. An at least five 

millimetre thick layer of plastic-modified cement mortar is applied in this case to a zinc 

covering of a weight of 200 g/m 2 . This coating is able to withstand extreme mechanical 

loads and is resistant to scoring by pointed fragments with the burst lining technique or 

by stones with the directional drilling technique. In the unlikely event of damage being 

done to this coating, the zinc covering is still available to provide active protection and its 

effect operates for a distance of up to 20 millimetres. 

9

A consideration of the economics of trenchless techniques, Reference documents 

The advantage of ductile cast iron pipes whose effect is most far-reaching is the connecting 

technology using the longitudinal force-fit BLS ® restrained joint. This is due in the first 

place to the tractive force permitted for the material of the pipes, which is the highest 

for any of the materials used in the water supply industry (section 2, Fig. 2.19). When 

part-strings are required, this has a beneficial effect on their lengths. In the second place 

however, the most important prerequisite for economy is the short assembly time for 

the BLS ® joint. The fact that single pipes can be assembled means that short installation 

pits and point sites are possible and that the speed of installation is determined by the 

time taken to change over the drilling and traction linkages at the machine end. The full 

permitted tractive forces can be applied the moment the short process of assembling the 

joint has been completed; there is no cooling time and no need for temperature-related 

reductions. These facts are the key to economic success when using ductile cast iron 

pipes for trenchless installation and renovation techniques. 


Cast iron is the oldest material used for industrially manufactured water pipes. Approximately 

half of the existing water supply network consists of pipes made of materials 

falling within this group. The resistance of ductile cast iron pipes and their long life is the 

basis for the excellent experience that has been had with them in practice, experience 

which has once again been corroborated in very recent times [9.7 and 9.8] 


<strong>Buderus</strong> Giesserei Wetzlar GmbH is an important manufacturer in the German cast iron 

pipe industry and it is precisely in very recent times that, with its technical developments 

for trenchless installation techniques, it has shown itself to be a pioneer, though without 

of course losing sight of the ties it has with the traditional techniques. For <strong>Buderus</strong> 

Giesserei Wetzlar GmbH reliable supply and continuity of its systems have always been 

the supreme commands in a customer-oriented business strategy which will continue to 

contribute to the success of the group in the future. 


[9.1] Steinhauser, P.: Wirtschaftlichkeitsbetrachtungen, Betrachtungen bei der 

grabenlosen Erneuerung. [Economic considerations, considerations relating 

to trenchless renovation]. Script of a talk given at the NO DIG Seminar on 

trenchless renovation of old, damaged pipes. Hanover Technical Academy, 

18.01.2007 

9

[9.2] DVGW-Hinweis W 09: Auswirkungen von Bauverfahren und Bauweise auf 

die Wirtschaftlichkeit von Betrieb und Instandhaltung (operative Netzkosten) 

der Wasserverteilungsanlagen, Jan. 2007 

[Effects of the construction procedure and method on the economy of 

the operation and maintenance (on the network operating costs) of water 

distribution systems, Jan. 2007] 

[9.3] Sommer, J.: NODIG-WALKING-Friedrichshafen 

Markus Mendek von der Stadtentwässerung Friedrichshafen erhält Goldenen 

Kanaldeckel 200 für Erneuerung im Berstlining-Verfahren 

[Markus Mendek of Friedrichshafen Civic Drains and Sewers Utility awarded 

the 200 Golden Manhole Cover for renovation by the burst lining method] 

[9. ] Levacher, R.: Erneuerung einer Verbindungsleitung DN 00 zwischen zwei 

Wasserwerken im Berstlining- und Spülbohrverfahren 

[Renovations of a DN 00 connecting pipe between two waterworks by the 

burst lining and directional drilling methods] 


[9. ] Emmerich Peter, Schmidt Rainer: Erneuerung einer Ortsnetzleitung im 

Berstlining-Verfahren 

[Renovation of a pipeline in a local system by the burst lining method] 


[9. ] DVGW Wasser-Information Nr. : DVGW-Schadenstatistik Wasser 

Auswertungen für die Erhebungsjahre 1997-1999 

[DVGW Water Information Release No. : DVGW Water Industry Damage 

Statistics – Assessments for the years surveyed 1997-1999] 

[9.7] Hannemann, B. und Rau, L.: Duktile Gussrohre aktuell wie eh und je 

[Ductile cast iron pipes just as up-to-date as ever] 

GUSSROHRTECHNIK 1 (2007), p. 

[9.8] Barthel, P.: Moderne Wasserversorgung – natürlich mit Gussrohren! 

[Modern-day water supply – with cast iron pipes of course!] 

GUSSROHRTECHNIK 1 (2007), p. 2 


97

Technical data sheets 

10.Technical data sheets 

Socket pressure pipes with BLS ® restrained joints 

to DIN EN 545/598 

Inside: cement mortar lining (CML) 

Outside: cement mortar coating (ZMU) 

98 

DN Dimensions [mm] [bar] Weight [kg] ≈ 

Ø d 1 

CML 

s 

PFA 1) ZMU 

per m pipe 

One pipe 2) 

Body length 

m 

80 3) 98 110 19. 92.2 

100 3) 118 100 2 113. 

12 1 100 28 139.7 

1 0 170 7 33 1 .1 

200 222 3 3 228. 

2 0 27 2 30 .2 

300 32 0 3 38 .1 

00 29 30 82 89. 

00 23 30 101 807. 

00 3 32 121 1037 

700 738 2 1 0 13 

800 8 2 1 /2 3) 1 0 1 

900 9 1 /2 3) 179 200 

1000 10 8 10/2 3) 199 2382 

1) PFA: Allowable component operating pressure in bars, DN 80 - DN 250 inc. high-pressure 

lock; higher pressures available in request 

2) Inc. cement mortar lining and thrust locking chamber, wall thickness class K9 

3) Wall thickness class K10 

Body length = m

BLS ® restrained joint 

DN 80 to DN 500 

DN 

Dimensions [mm] 

Ø d 1 Ø D 1) t 

PFA 2)* 

Possible 

angular deflection 

3) 

Number 

of locks 


Lock 

set 

[kg] 

80 ** 98 1 127 110 ° 3 0.70 

100 ** 118 182 13 100 ° 3 0.83 

12 1 20 1 3 100 ° 3 1.13 

1 0 170 239 1 0 7 ° 3 1.3 

200 222 293 1 0 3 ° 3 1.9 

2 0 27 3 7 1 ° 3 2.70 

300 32 10 170 0 ° 2.70 

00 29 21 190 30 3° . 0 

00 23 3 200 30 3° . 0 

1) Guideline value 

2) PFA: Allowable component operating pressure in bars, up to DN 250 

includes high-pressure lock 

3) When of the nominal dimensions 

*) Basis for calculation is wall thickness class K9; higher pressures available on request 

**) Wall thickness class K10 

Retaining chamber 

Left lock 

Catch 

Right lock 

Welding bead 

TYTON ® gasket 

Socket 

99


BLS ® restrained joint 

DN 600 to DN 1000 

100 

DN 


Locking 

segment 

Dimensions [mm] 

Ø d 1 Ø D 1) t 

Welding bead 

PFA 2) 


Possible 

angular 

deflection 

Socket 

Number of 

locks 

Clamping 

rings 

00 3 732 17 32 2° 9 9 

700 738 8 9 197 2 1. ° 10 11 

800 8 2 9 0 209 1 /2 3) 1. ° 10 1 

900 9 1073 221 1 /2 3) 1. ° 13 13 

1000 10 8 1188 233 10/2 3) 1. ° 1 1 

1) Guideline value 

2) PFA: Allowable component operating pressure in bars, up to DN 250 includes high-pressure 

lock 

3) Wall thickness class K10 

Note: The locking segments must be fixed in place with a clamping strap! See installation 

instructions


101

Installation instructions 

11.Installation instructions 

11.1 General 

Applicability 

These installation instructions apply to DN 80 - DN 00 ductile cast iron pipes and fittings 

with longitudinal force-fit BLS ® restrained joints. 

Where appropriate the installation instructions for pipes with cement mortar coatings 

(ZMU) should be followed. 

For very high internal pressures (e.g. in snow making facilities) and for trenchless installation 

techniques (e.g. the press-pull, rocket plough or horizontal directional drilling 

techniques) an additional high-pressure lock has to be used (see section headed „Highpressure 

lock“). 

In the case of buried pipelines, the number of joints to be locked has to be decided in 

accordance with DVGW Arbeitsblatt GW 3 8. 

The permitted tractive forces for trenchless installation techniques are laid down in 

DVGW Arbeitsblätter GW 321, 322-1, 323 and 32 (draft), or see section 2, page 20. 

Bundling, transport and storage 

Pipes of up to DN 3 0 size are supplied bundled 

102 

DN 

Pipes 

80 100 12 1 0 200 2 0 300 3 0 

per 

bundle 

1 1 10 

To stop the pipes from being damaged or fouled, wooden supporting timbers and 

spacing blocks should be used both when the pipes are being stored temporarily and 

when they are being laid out along the run. 

The steel straps holding the bundles of pipes together must only be removed with tinsnips 

or side cutters. Chisels, crowbars and certainly pickaxes will damage the outside 

protection that the pipes have.

General 

Pipes must not be: 

• dropped or put down with a jolt, 

• thrown off the vehicle, 

• rubbed against surfaces or rolled for long distances. 

Slinging straps should be used for loading and unloading pipes. If single pipes are unloaded 

with crane hooks, this must be done with long padded hooks which are hooked 

in at the ends of the pipes, as otherwise the local pressure on the layer of cement mortar 

will be too high. Particularly with large sizes of pipe, a shoe matched to the shape 

of the pipe must be fitted under the crane hook to protect the cement mortar lining 

from damage. 

If ductile cast iron pipes are stored in a stack, they should be put down on lengths of 

timber at least 10 centimetres wide spaced about 1. metres away from the ends of the 

pipes. Damage to the inside or outside protection should at once be carefully repaired 

Maximum permitted stacked heights 

DN Layers 

80 - 1 0 1 

200 - 300 10 

3 0 - 00 

700 - 1000 2 

For reasons of accident prevention, stacked heights of more than 3 metres should be 

avoided. 

103


Pipe closures 

Pipes to DN EN with cement mortar linings are supplied fitted with pipe closures 

which are intended to stop the interiors of the pipes from becoming fouled. The closures 

should not be removed until immediately before the pipes are going to be connected. 

Treatment of gaskets on the site 

To ensure that the pipeline will be reliable in operation, only the gaskets meeting the 

relevant quality requirements which are supplied by the manufacturer of the cast iron 

pipes must be fitted. 

The gaskets must be stored in an undeformed state in cool and dry conditions. They 

should be protected from direct sunlight. Care must be taken to see that they are not 

damaged or fouled. 

There is a certain increase in the hardness of the gaskets at temperatures of less than 

0°C. Where the outside temperatures are below 0°C, the gaskets should therefore be 

stored at a temperature of more than 10°C to make them easier to fit. 

The gaskets should not be removed from the place where they are stored until immediately 

before they are fitted. 

Pipe pits and bedding of the pipes 

The pipe pit should be set up in accordance with the existing technical specifications. 

These are, amongst others: DIN EN 80 , DIN EN 1 10, DIN 18 300, DIN 12 , 

DIN 0 929 part 3, DIN 30 37 part 2, DVGW Arbeitsblätter W 00-2 or GW 9, ATV 

DVGW Arbeitsblatt 139 and the technical bulletin for the filling of pipeline trenches. 

Installation 

The installation of pipes and fittings should be carried out in accordance with our installation 

instructions. If the soil in-situ is aggressive (see DIN 0 929, part 3 and DVGW Arbeitsblatt 

GW 9 on this point), a satisfactory enclosing layer of sand should be applied. 

When installation is in highly aggressive soils, we recommend pipes with cement mortar 

coatings (ZMU) to DIN EN 1 2. 

Pipe coatings should be decided on in accordance with the fields of use shown in 

DIN 30 7 -2. 

10

Filling in the pipe pit 

DN 80 - DN 00 BLS ® joints 

The pipe pit in the pavement should be filled in accordance with the „Merkblatt für das 

Verfüllen von Leitungsgräben“ [Directions for the filling of pipeline trenches] issued by 

the Road and Traffic Research Society (FGSV) of Cologne and with the „Zusätzliche 

Technische Vertragsbedingungen und Richtlinien for Erdarbeiten im Strassenbau“ [„Additional 

Technical Contractual Conditions for Earthmoving Work in Roadbuilding“] (ZTV 

E - StB 9 ). 

Pressure testing 

The documents that govern the execution of pressure tests on water pipelines are 

DIN EN 80 and DVGW Arbeitsblatt W 200-2. 

11.2 Installation instructions for 

DN 80 to DN 500 BLS ® joints 

Construction of the DN 80 - 

DN 500 joint 

Cleaning 

The locks and those surfaces of the seating 

for the gasket, the retaining groove and the 

locking chamber which are indicated by arrows 

should be cleaned and any build-ups 

of paint should be removed. 

A scraper, e.g. a bent screwdriver, should 

be used to clean the retaining groove. 

Clean the inserting end. 

Retaining 

chamber 

Left 

lock 

Catch 

Right lock 

Welding bead 


Socket 

Inserting end 

10


Carefully wipe a thin layer of the lubricant 

supplied by the pipe manufacturer 

onto only the surfaces which are shown 

hatched. 

Assembling the joint 

Fitting the TYTON ® gasket 

Clean the TYTON ® gasket and pull it into 

a heart shape 

Insert the TYTON ® gasket into the socket 

in such a way that the external claw of hard 

rubber engages in the retaining groove in 

the socket 

Then press the loop in the gasket flat. 

If you have difficulty pressing the loop flat, 

pull out a second loop on the opposite 

side. These two small loops can then be 

pressed flat without any trouble. 

10


There must never be a gap between the inner edge of the hard rubber of the TYTON ® 

gasket and the locating bead. 

Right 

Apply a thin film of lubricant to the TYTON ® gasket. 

Apply a thin film of lubricant to the inserting 

end, and particularly the bevel, and 

then insert it into the socket until it is resting 

concentrically against the TYTON ® 

gasket. The axis of the pipe or fitting which 

is already in place and the axis of the one 

which is going to be pulled in must be in a 

straight line with one another. 

Wrong 

Positions of the openings in the socket when in the pipe pit 

DN 80 to DN 2 0 DN 300 to DN 00 

For the locks to be inserted or the clamping strap to be screwed up, it is advisable for 

the positions of the openings in the socket to be as shown. 

In the case of fittings, the positions of the openings will be governed by the installation 

situation. 

107


Inserting end with welding bead 

The inserting end having been cleaned, particularly at the bevel, wipe a thin film of lubricant 

over it and push or pull it in until it butts against the end-wall of the socket. The 

pipes must not be deflected to an angle when the locks are being inserted. 

1) Insert the „right“ lock (1) in the opening in the socket and move it clockwise until it 

will not move any further. 

2) Insert the „left“ lock (2) in the opening in the socket and move it anti-clockwise until 

it will not move any further. 

3) Press the catch (3) into the opening in the socket 

On pipes of DN 300 size and above, steps 1 to 3 have to be performed twice, because 

2 x 2 locks and two catches are inserted in this case. 

A high-pressure lock should always be used 

for trenchless installation techniques using 

DN 80 to DN 2 0 size pipes (see p. 11 ). 

Inserting end with no welding bead 

(not suitable for trenchless installation!) 

1.) Insert the split clamping ring. The two halves of the clamping ring are first inserted 

in the thrust locking chamber separately and are then loosely connected with the 

two bolts. 

2) Mark the depth of penetration (= the depth of the socket) on the inserting end. 

3) Pull in the inserting end. The inserting end having been cleaned, particularly at the 

bevel, wipe a thin film of lubricant over 

it and push or pull it in until it butts 

against the end-wall of the socket. The 

pipes must not be deflected to an angle 

when it is being pulled in. After the 

inserting end has been pulled in, the 

previously made mark which it carries 

should be almost in line with the end-face of the socket. 

) Pull the clamping ring as far as is possible towards the end-face of the socket and 

then tighten the bolts to a torque of at least 50 Nm! 

108 

3 

1 

Do not remove 

the lifting device 

until the joint has 

been made 

2

Use of clamping ring joints 


When clamping ring joints are used, care must be taken to see that they are not used in 

socketed bends, EN-pieces and the like! 

For this purpose the length of pipe for mating purposes which is cut off, which has two 

smooth ends, is turned through 180° so that the end carrying the welding bead can be 

inserted in the socket of the bend. Before the short pipe that is left, which has a socket, 

is fitted, an uncut pipe is connected on and it is only in the socket of this latter that the 

inserting end without a welding bead is inserted. 

Factory-made 

welding bead On-site cut 

Direction of laying 

Lock joint 

(has a welding bead) 

Note on the use of clamping rings 

Clamping ring joint 

(no welding bead) 

Uncut pipe carrying 

a welding bead 

Clamping ring joint 

(no welding bead) 

Lock joint 

(has a welding bead) 

Before clamping rings are used in bridge or culvert pipes, and before they are fitted 

on steep slopes, in protective pipes or in collector pipes, our Applications Engineering 

Division should be consulted. The use of clamping rings should be avoided in these cases 

and in trenchless installation techniques. Pipes for mating purposes which are required 

should be provided with welding beads (see the section headed „Retrospective application 

of welding beads“). 

109


Locking 

Pull or press the pipe out of the socket until the locks or the locking ring, as the case may 

be, are in abutment in the locking chamber, using a laying tool for example. 

The joint is now locked against longitudinal forces. 

Angular deflection 

Once the joint has been made, pipes of the nominal dimensions shown can be deflected 

to the following angles: 

DN 80 to DN 1 0 – ° 

DN 200 to DN 300 – ° 

DN 00 and DN 00 – 3° 

For a pipe metres in length, an angular deflection of 1° gives a movement off the axis 

of the pipe or fitting fitted previously of about 10 centimetres, i.e. a deflection of 3° = 

30 centimetres. 

110

Notice on assembly 


It should be borne in mind that, as a function of the internal pressure and the tolerances 

on the joints, stretches of up to about eight millimetres per joint may occur. 

To allow for the amount by which the pipeline moves outwards when stretched by pressure, 

the pipes should be offset inwards at all bends by deflecting the joints inwards to 

their maximum permitted angular deflection. See the diagram below. 

Shortening pipes 

Attention must be paid to the ability of 

pipes to be cut. Up to and including the 

DN 300 size, any pipe can be cut at up to 

a metre back from the socket. At DN 00 

and above, pipes which can be cut are 

specially identified by a lengthwise white 

stripe or the letters „SR“ printed on the 

end-face of the socket. 1 m 

Tools 

Position after 

stretching 

Position when 

installed 

The most suitable pieces of equipment for cutting ductile cast iron pipes are disc cutters 

and grinders with drives of various sorts such for example as compressed air, electric 

motors or petrol engines. 

The cutting discs we recommend are silicon carbide discs of the C 2 RT Spezial type. 

These are cutting discs for stone which have proved successful in practice for the cutting 

of ductile cast iron pipes. 

When pipes lined or coated with cement mortar are being cut, protective goggles and 

respiratory protection must be worn. 

45° 

111


Any ground-off material which occurs must be carefully cleaned out of the inside of 

the pipe. 

With pipes of large nominal sizes, it may 

happen that the new inserting ends which 

exist after the shortening are slightly oval. If 

necessary, inserting ends of this kind must 

be made round again with suitable devices 

which are applied to the inside or outside 

of the pipe, such for example as hydraulic 

jacks or mounting clamps. The device 

should not be removed until the joint has 

been completed. 

Machining of cut faces 

Pipes which are shortened on site must be bevelled at the cut faces to match the original 

inserting end. 

The bevel must be made as shown in the diagrams below. 

The bright metal face should be painted with bituminous paint (or equivalent) which is 

suited to the external protection on the pipe. What is suitable for this purpose is a quickdrying 

cover coating which meets the requirements of the German Foodstuffs Law. 

For quicker drying, it is advisable for the ends of the pipe to be warmed beforehand, and 

the paint itself afterwards, with a gas burner. 

112 

3-4 

DN 80 to DN 00 DN 700 to DN 1000 

10-12 

5-6 

20-22 

Slightly radiused Slightly radiused 

Block of timber 

Block of timber

Retrospective application of welding beads 


If pipes have to be shortened on site, the welding bead needed for the BLS ® restrained 

joint has to be applied using an electrode laid down by the manufacturer. The welding 

work is to be carried out as directed in DVS Merkblatt 1 02. 

The size of the bead and its distance from the inserting end are to be as shown in the 

table below. 

Type of electrode, e.g. Castolin 7330-D 

DN 80 100 12 1 0 200 2 0 300 00 00 

a 8 ± 91± 9 ± 101± 10 ± 10 ± 10 ± 11 ± 120± 

b 8±2 8±2 8±2 8±2 9±2 9±2 9±2 10±2 10±2 

c +0, 

-1 

+0, 

-1 

+0, 

-1 

+0, 

-1 . +0. 

-1 . +0. 

-1 . +0. 

-1 

+0. 

-1 

+0. 

-1 

To ensure that the welding bead is properly Copper clamping ring 

b 

made and uniform, a copper clamping ring 

must be fastened in place on the inserting 

end to enable the welding bead to be applied 

at the correct distance from the end 

(see table). 

The zone in which the weld is made must be 

bright metal. Contaminants or zinc coatings 

must be removed by filing or grinding. 

c 

Once the copper clamping ring has been removed, the cut edge at the inserting end 

must be restored to the original form and both it and the region occupied by the welding 

bead must be cleaned. Finally, these regions must be provided with the appropriate 

protective coating. 

Disconnecting 

Push the pipe into the socket until it is in abutment. Take out the catch through the opening 

in the socket. Move the locks and remove them through the opening in the socket. 

If there is a high-pressure lock, use a shallow object (e.g. a screwdriver) to push it away 

from the floor and to the opening in the socket and take it out. 

a 

113


Disconnecting clamping ring joints 

Push the pipe into the socket in the axial direction until it is in abutment. 

The bolts holding the clamping ring together having been removed, loosen the halves 

of the clamping ring by hitting them with a hammer. While disconnection is proceeding, 

make sure that the halves of the clamping ring stay loose (if necessary repeat the hammering 

process while the inserting end is being pulled out). The clamping ring can also be 

prevented from jamming against the inserting end when the joint is being disconnected 

by clamping a square metal bar between the arms of the clamping ring. Under no circumstances 

must the socket or the main body of the pipe be hit with the hammer! 

The high-pressure lock 

For very high internal pressures (e.g. in the case of snow making facilities and pipelines for 

turbines) and for trenchless installation techniques (e.g. the press-pull, rocket plough or 

horizontal directional drilling techniques), an additional high-pressure lock has to be used. 

The high-pressure lock is inserted in the locking chamber through the opening in the socket 

and is positioned at the floor of the socket before the right and left locks are inserted. The 

locks can then be inserted, which means that the high-pressure lock is situated between 

their smooth ends. The locks are then fixed in place with the catch in the usual way. 

Shown in the illustration below is a fully assembled BLS ® socket including a high-pressure 

lock. The high-pressure lock is used for nominal sizes from DN 80 to DN 2 0. 

11 

Left lock 

Catch 

High-pressure lock 

Right lock

11.2 Installation instructions for DN 600 - DN 1000 BLS ® joints 

Applicability 


These installation instructions apply to 

ductile cast iron pipes and fittings with longitudinal 

force-fit BLS ® restrained joints. 

Where appropriate the installation instructions 

for pipes with cement mortar coatings 

(ZMU) should be followed. 

In the case of buried pipelines, the number of joints to be locked has to be decided in accordance 

with DVGW Arbeitsblatt GW 3 8. 

The permitted tractive forces for trenchless installation techniques are laid down in DVGW 

Arbeitsblätter GW 321, 322-1, 323 and 32 (draft), or see section 2, page 20, Table 2.1. 

Construction of the DN 600 - DN 1000 joint 

X 

Retaining chamber Welding bead 

Locking 

segment 

Clamping 

strap 

Inserting end 


Number of locking segments per joint 

Socket 

Openings in socket 

View on X 

DN 00 700 800 900 1000 

n 9 10 10 13 1 

11


Cleaning 

The locking segments and those surfaces of the seating for the gasket, the retaining 

groove and the locking chamber which are indicated by arrows should be cleaned and 

any build-ups of paint should be removed. 

A scraper, e.g. a bent screwdriver, should be used to clean the retaining grooves. 

Clean the inserting end. 

Assembling the joint 

Fitting the TYTON ® gasket (see pp. 10 -107) 

The opening in the end-face of the socket should always be positioned at the crown of 

the pipe. Use the laying tool to push the inserting end of the pipe into the socket of the 

pipe which is already in place until it is in abutment. 

11

Inserting the locking segments 


The joint must not be deflected angularly when the locking segments are being fitted. 

First insert the locking segments through the opening in the socket and then distribute 

them around the circumference working alternately left and right. Then rotate all the 

segments in one direction so that the last segment can be inserted through the opening 

in the socket and moved to a position where the joint is securely locked. 

Only a small part of the humps on the last locking segment must be visible through the 

opening in the socket. If any segments happen to jam, they should be moved to their 

intended position by moving the pipe as it hangs from the sling and tapping them gently 

with a hammer. 

Under no circumstances must the socket or the main body of the pipe be hit with the 

hammer! 

Locking 

Pull all the segments back towards the 

outside until they butt against the bevel of 

the locking chamber. Then fit the clamping 

strap over the segments in the way shown. 

Then tighten the clamping strap, but only 

gently so that the segments can still be 

moved. Now line the locking segments 

up properly. They must lie completely flat 

against the body of the pipe and they must not overlap. Then tighten the clamping strap 

up sufficiently tight for the locking segments to bear firmly against the pipe around the 

whole of its circumference. It is now no longer possible for the locking segments to be 

moved. Apply axial traction (e.g. with a locking clamp) and pull the pipe out of the joint 

until the welding bead comes to rest against the segments. 

When the joint is in an undeflected state, the longitudinal distances from the locking 

segments to the end-face of the socket should all the approximately the same. 

117



Locking 

segment 

Clamping strap 

User information for ratchet-equipped clamping strap 

Clamping: 

1. Thread in the clamping strap 

2. Pull it through by hand to the desired 

length (to pre-tension it) 

3. Tighten the clamping strap by moving 

the handle up and down 

Releasing: 

. This is done by pulling on the locking 

pawl and at the same time moving the 

lever through 180° to the opposite 

position. 

. Pull the clamping strap out by hand. 

General directions for use 

The ratchet-equipped clamping strap must not be adversely affected by the corners on 

the segments. The different types are suitable for the following temperature ranges: 

PES: - 0°C to 100°C / PA: -20°C to 100°C / PP: - 0°C to -80°C. The temperature 

ranges may vary in a chemical environment (where this applies, check with the manufacturer 

or supplier). 

Storage: in clean, dry and well ventilated surroundings, well away from any heat source. 

Keep away from chemicals and flue gases. Do not expose to direct sunlight or other 

ultraviolet radiation. Clamping straps must not be used as lashings! Check clamping 

straps for damage before they are used and never use them if: the clamping strap is 

damaged or a connecting or clamping component is severely abraded, torn or cracked, 

broken as a result of scuffing, fractured/distorted or severely corroded. 

• Never exceed the permitted tractive forces (shown on the label) 

• Do not twist or knot the straps. 

118 

Welding bead TYTON ® gasket 

Socket 

Inserting end

Angular deflection 


Once the joint has been made, pipes of the nominal dimensions can be deflected to the 

following angles: 

DN 00 – 2,0° 

DN 700 – 1, ° 

DN 800 – 1, ° 

DN 900 – 1, ° 

DN 1000 – 1, ° 

For a pipe metres in length, an angular deflection of 1° gives a movement off the axis 

of the pipe fitted previously of about ten centimetres, i.e. a deflection of 3° = 30 centimetres. 

Notice on installation and laying 

It should be borne in mind that, because the locking segments adjust as a function of the 

internal pressure, stretches of up to about eight millimetres per joint may occur. 

To allow for the amount by which the pipeline moves outwards when stretched by pressure, 

the pipes should be offset inwards at all bends by deflecting the joints inwards to 

their maximum permitted angular deflection. See the diagram below. 

Position after 

stretching 

Position when 

installed 

45° 

119


Shortening pipes 

Attention must be paid to the ability of pipes to be cut (see p. 111). 

Pipes which can be cut are identified by a lengthwise white stripe or the letters „SR“ 

printed on the end-face of the socket. 

If pipes have to be shortened on site, the welding bead needed for the BLS ® restrained 

joint has to be applied using an electrode laid down by the manufacturer. The welding 

work is to be carried out as directed in DVS Merkblatt 1 02. 

The size of the bead and its distance from the inserting end are to be as shown in the 

table below. 

Type of electrode, e.g. Castolin 7330-D 

120 

DN 00 700 800 900 1000 

a 117 0 13 0 

1 0 1 0 0 1 00 

-2 

-2 

-2 

-2 

-2 

b 8±1 8±1 8±1 8±1 8±1 

c 

+0. 

0 

Combining fittings belonging to other systems with BLS ® joints 

+0. 

0 

When pipes end are going to be fitted to 

fittings belonging to other systems, our 

Applications Engineering Division should 

be consulted. 

+0. 

0 

Copper clamping ring 

To ensure that the welding bead is properly made and uniform, a copper clamping ring 

must be fastened in place on the inserting end to enable the welding bead to be applied 

at the correct distance from the end (see table). 

The zone in which the weld is made must be bright metal. Contaminants or zinc coatings 

must be removed by filing or grinding. 

Once the copper clamping ring has been removed, the cut edge at the inserting end 

must be restored to the original form and both it and the region occupied by the welding 

bead must be cleaned. Finally, these regions must be provided with the appropriate 

protective coating. 

+0. 

0 

b 

a 

+0. 

0 

c

Disconnecting 

BLS ® joint disconnection 

Push the pipe into the socket in the axial direction until it is in abutment and take out the 

locking segments through the opening in the socket. 

Laying equipment and aids 

The following items of laying equipment and aids are available for assembling joints and 

fittings 

Laying equipment: 

DN Pipes Fittings 

80 

MMA, MMB, MMR 

100 

Lever and flanged so- Socket-bend: laying tool (e.g. V 301) 

12 

80 

100 

ckets: Lever 

12 

1 0 

Laying tool 

V 301 

200 

2 0 

300 

(3 0) 

00 

00 

00 

V 301 V 302 

(ZMU) 

V 302 + chain-equipped fork tool of V 301 

700 

800 

900 

1000 

Rack assembly Rack assembly 

Aids: 

Dusting brush, cotton waste, wire brush, spatula, scraper (e.g. bent screwdriver), paint 

brush, lubricant, tracer. 

121


11.3 Installation instructions for ductile cast iron pipes with cement mortar coatings 

(ZMU) 

Applicability 

These installation instructions apply to the 

installation of ductile cast iron pipes to 

DIN EN with cement mortar coatings 

(ZMU) to DIN 1 2. 

To make the joints, the installation instructions 

which apply in the respective cases 

should be followed. 

What also apply are the guidelines given in DIN EN 80 and DVGW Arbeitsblatt 

GW 00-2 (for water pipelines) or DIN EN 10 and ATV-DVWK A 138 (for waste water 

pipelines). 

Installation 

Installation must be carried out in such a way that the ZMU is not damaged. 

The following options are available for protecting the restrained joints 

• a cement mortar protecting sleeve 

• shrink-on material or protective tapes (to DIN 30 72), 

• a mortar bandage (e.g. as produced by Messrs. Ergelit) for special applications. 

Cement mortar protecting sleeves 

Cement mortar protecting sleeves can be used on TYTON ® and BRS ® restrained joints 

up to DN 700 and on BLS ® restrained joints up to DN 00. 

Before the joint is assembled, the sleeve is rolled on and, with the larger diameter leading, 

is pulled onto the inserting end sufficiently far for the ZMU to project by approx. 

100 millimetres. 

Fitting can be simplified by applying lubricant to the ZMU. 

Once the joint has been assembled and the seating of the gasket checked with the tracer, 

the sleeve is folded over, pulled to the end-face of the socket and rolled over the socket. 

It then rests firmly and closely in place. 

122

Shrink-on devices and protective 

tapes 

As an alternative to the cement mortar 

protecting sleeve, the joint region can 

also be protected with shrink-on devices 

or protective tapes. The shrink-on device 

must be suitable for the dimensions of the 

particular joint involved. 

Applying a shrink-on collar 

The shrink-on collar has to be pulled over 

the socket end before the joint is made. 

The surface to be enclosed has to be prepared 

in accordance with DVGW Merkblatt 

GW 1 , i.e. the region has to be 

freed of rust, grease, dirt and loose particles. 

The surface must be pre-heated to 

approx. 0°C with a propane gas flame set 

to a soft setting and thus dried. 

The shrink-on collar is then pulled over the 

joint until it is central on it and the protective 

backing on the inside is then removed. 

At the point where the end-face of the 

socket is situated, the shrink-on collar is 

then heated evenly, all round, with a propane 

gas flame set to a soft setting until 

the shrinking process begins and the sleeve 

starts to assume the outline shape of the 

socket. Then, while keeping the temperature 

even, which should be done by 

moving the burner in the circumferential 

direction while fanning it from side to side, 

the part of the collar around the socket is 

first shrunk on, and then, starting from the 

end-face of the socket, the part around the 

main body of the pipe. 

~ 100 

ZMU 

123


The operation has been properly carried out if 

• the whole of the collar has been shrunk onto the joint between the pipes, 

• it rests down flat, without any cold spots or air bubbles, and the sealing adhesive has 

been pressed out at both ends, 

• the 0 millimetre overlap that is required over the cement mortar coating has been 

achieved. 

Wrapping with mortar bandage (produced by the Ergelit company) 

Soak the mortar bandage thoroughly in a water-filled bucket until no air bubbles are being 

released. This should take a maximum of two minutes. 

Take out the wet bandage and squeeze it gently. 

Wind the bandage onto the area that is to be enclosed (cover ≥ 50 mm of the ZMU) 

and match it to the outline. 

To give a six millimetre thick layer, wind the bandage round twice or make a 0% 

overlap. 

This post-insulation is able to accept mechanical loads after one to three hours. 

Filling the pipe pit 

The bedding for the pipes should be laid in accordance with DIN EN 80 / DVGW W 

00-2 or DIN 1 10/ATV-DVWK A 139, as the case may be. 

Virtually any excavated material, even soils containing stones up to a grain size of 100 

millimetres, can be used as infill (see DVGW Arbeitsblatt W 00-2). An enclosing layer of 

sand or foreign material is only necessary in special cases. 

In the region of traffic-carrying surfaces, the Merkblatt for the filling of pipelines trenches 

(issued by the Road Research Company of Cologne) should be followed. 

Restrained joints protected with cement mortar protecting sleeves or shrink-on devices 

should be enclosed in fine-grained material or protected with pipe protecting mats. 

Shortening of pipes 

Up to the DN 300 size, the pipes supplied are able to be cut in the region of their main 

body, at a point up to one metre away from the end-face of the socket, to enable a 

connection to be made. 

Above the DN 300 size, only pipes which carry a continuous, white, lengthwise strip are 

able to be cut. Pipes of this kind (cuttable pipes) have to be ordered separately. 

An additional identifying mark for a cuttable pipe is an „SR“ on the end-face of the socket. 

12

ZMU 

Before a pipe is cut, the ZMU should be removed for a length of 2 L or 2 LS, as the case 

may be, as shown in the table below. (Where there are collars, the dimension for the 

fitting of the collar should be taken into account as well). 

DN 

L 

2 L 

TYTON ® /BRS ® 

L [mm] 

Ls 

2 Ls 

BLS ® 

L S [mm] 

80 9 1 

100 100 17 

12 100 18 

1 0 10 190 

200 110 200 

2 0 11 20 

300 120 210 

(3 0) 120 – 

00 120 230 

00 130 2 

00 1 300 

700 20 31 

800 220 330 

900 230 3 

1000 2 3 0 

In the case of TYTON ® , the ZMU-free length at the inserting end applies for sockets 

complying with 

DIN 28 03 up to DN 00, shape A 

DN 700 and above, shape B (restrained socket) 

The ZMU is cut into, to approximately half the thickness of the ZMU layer, around the 

entire circumference of the pipe. When this is done, care must be taken not to damage 

the cast iron pipe. 

The ZMU is then also cut into in the longitudinal direction between the two circumferential 

cuts. All the cuts are then forced apart with a chisel. After this the ZMU can 

be detached all round by tapping it gently with a hammer, starting at a point where it is 

12


split longitudinally. On pipes of DN 700 - DN 1000 sizes, it may be necessary, before 

the ZMU is detached, for it to be heated with a propane gas flame. The inserting end 

should be cleaned with a scraper and a wire brush. 

The pipes can then be cut with disc cutters or grinders. Cutting discs for stone are suitable 

for cutting the pipes, e.g. the C 2 RT Spezial type. 

Protective goggles and respiratory protection must be worn when cutting pipes. 

The cut edge should be bevelled to match the original inserting end using a hand-held 

grinder. Any material which is ground off has to be removed from the inside of the pipe. 

It is essential for the zinc covered inserting ends which are produced to be recoated 

with a suitable cover coating. 

Fitting of under-pressure tapping fittings 

When under-pressure tapping fittings are being fitted, the ZMU should be removed in 

the region of the sealing surface in such a way that the seal of the tapping fitting seals 

against the cleaned surface of the pipe. Once the tapping fitting has been fitted, the surface 

of the pipe which is still exposed should be re-insulated in the appropriate way. 

Alternatively, the ZMU can be smoothed in the region of the drilled hole with a handheld 

grinder or a rasp to a level below the net bandage. An under-pressure tapping 

fitting is placed on this region and sealed off on the ZMU. 

Another possibility is for the under-pressure tapping fittings used to be ones which seal 

in the drilled hole. See also DVGW Merkblatt W 333. 

On-site repair of the ZMU 

Parts of the ZMU which have come free may only be repaired with the repair kit which 

is supplied with the pipes by the pipe manufacturer. 

The repair kit contains a mixture of cement, sand and plastic fibres, gauze tape and a 

mortar hardener. The materials contained in the repair kit are mixed until a mortar 

able to be applied with a spatula is obtained. As dictated by the outside temperature, 

water can be mixed in what this is done. The damaged points on the ZMU are cleaned 

and wetted and mortar is then applied to them with a spatula. Damaged areas of any 

great size (larger than the palm of the hand) must be covered with gauze tape after the 

mortar has been applied. 

Where pipes have their cement coating repaired, a wait of at least twelve hours is recommended 

before they are installed or else the repaired area should be given adequate 

protection against mechanical stresses. 

12

ZMU 

127

128

129

130

131


Cast Iron Pipe Technology 

P.O. Box 1240 D-35573 Wetzlar 

Phone: +49 (0) 64 41 49 - 22 60 

Fax: +49 (0) 64 41 49 - 16 13 

E-Mail: export.gussrohrtechnik@guss.buderus.de 

www.gussrohre.com 

© BGW/RV • 035 • 06/08 • e 500 • DN

Buderus Manual on Trenchless Installation of Ductile Cast ... - Duktus

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