mohring engels.indd - Keramo Steinzeug

Cost-effective and environmentally
acceptable sewer and drain
construction using micro-tunnelling
A guide for planning and preparatory construction work · Dipl.-Ing. Knut Möhring, Berlin

Cost-effective and environmentally
acceptable sewer and drain construction
using micro-tunnelling
A guide for planning and preparatory construction work • Dipl.-Ing. Knut Möhring, Berlin
Translated under the supervision of Keramo-Steinzeug, Paalsteenstraat 36, B-3500 Hasselt,
from German into English, with the permission of Dipl.-Ing. Möhring

Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. The advantages of micro-tunnelling . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Methods of micro-tunnelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Non-controllable methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Controllable methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Pilot pipe jacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Thrust-bore pipe jacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Shield pipe jacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Selection criteria for jacking systems . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Micro-tunnelling applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1 The Berlin method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 Pipe eating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Planning and preparatory construction work . . . . . . . . . . . . . . . . . . . . 20
6.1 ATV Worksheet A 125 Pipe jacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.2 ATV Worksheet A 161 Structural design of jacking pipes . . . . . . . . . . . . . 21
6.3 Standard rating books, rating range 085 pipe jacking . . . . . . . . . . . . . . . . 21
6.4 DIN 18319 General technical contract terms for pipe jacking . . . . . . . . . . 21
6.5 Obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.6 Quality Safeguarding in Sewer Construction . . . . . . . . . . . . . . . . . . . . . . . 23
7. Cost-effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1 Comparative cost of sewer construction: unpaved surface . . . . . . . . . . . 25
7.2 Comparative cost of sewer construction: interlocking paving . . . . . . . . . 26
7.3 Comparative cost of sewer construction: concrete paving . . . . . . . . . . . . 27
7.4 Comparative cost of sewer construction: bitumen paving . . . . . . . . . . . . 28
7.5 Comparative cost of house-connection sewers . . . . . . . . . . . . . . . . . . . . 29
7.6 Social costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8. Micro-tunnelling as an opportunity for lower sewage charges . . . . . . 30
9. Recommendations for carrying out micro-tunnelling . . . . . . . . . . . . . . 31

Dipl.-Ing. Knut Möhring…
…former manager of the Supply Networks division of
Berliner Wasserbetriebe (BWB)
Involvement in standardisation and trade-association activities
(among others):
– chairman of the ATV DVGW ”Trenchless Construction
Techniques” working group
– member of numerous study groups in the DIN Water
Industry Standardisation Committee and of CEN Panels
– member of ATV HA 1
– former chairman of the DIN study group Vitrified Clay
Pipes
– former member of the Technical & Scientific Advisory
Panel of the Vitrified Clay Industry Research Association
– founder member and chairman for many years of the
Quality Safeguarding in Sewer Construction
Honours (among others):
– ATV Golden Needle
Dipl.-Ing. Knut Möhring
Nikolaus-Bares-Weg 81
12279 Berlin
– Order of Merit of the Federal Republic
1. Introduction
Micro-tunnelling Page 5
Methodical construction of the first generation of municipal
sewage systems of the modern era began in the
last century. Laid carefully, of good quality and at considerable
cost in manual labour, many of those sewers
and drains are still in use today.
For a long time technical advances in sewer construction
were only tentative, confined mainly to mechanisation
of work on-site, soil excavation and the introduction
of alternative techniques for lining utility trenches and
shafts. Construction-site pictures from earlier decades
show clearly that manual work predominated and that
sewer construction was very labour-intensive. Clear
economic advantages were obtainable only after tunnelling
methods became possible in the construction of
accessible sewers. This depended on high-grade pipes
and joint assemblies together with efficient hydraulic
pressing and conveying equipment in conjunction with
reliable measurement and control systems. In particular
where collecting-drains were needed at great depth below
the water table significant savings could be made
with these ”manned” thrust borings as against opentrench
sewer construction. Such headings are routine
today. Jacking-distances of over 1000 metres from a
single starting shaft are just as possible as the driving of
three-dimensional curves. Even differing geological
conditions present no problems, since pipe- and shieldjacking
systems are possible for accessible sewers in all
loose and consolidated rock and in groundwater.
With ”manned” thrust borings it is however essential to
observe safety rules relating to minimum dimensions in
the working-space in the pipe. In circular walk-through
tunnels, galleries or headings
for lengths up to
50 metres 800 mm unobstructed internal diameter
and for lengths over
50 metres 1000 mm unobstructed internal diameter
must be observed. Circular sections not meeting these
requirements were deemed non-accessible. Today’s
regulations under ATV Worksheet A 125 Pipe jacking,
September 1996, stipulate for ”manned” pipe jacking a
normal bore of 1,200 mm, which may in exceptional
cases be reduced to 1,000 mm if
– a jacking distance of 80 metres is not exceeded and

m
350.000
300.000
250.000
200.000
150.000
100.000
50.000
0
Page 6 Micro-tunnelling
– there is a linked working pipe (bore 1,200 mm) at least
2,000 mm in length.
A glance at German sewage systems shows them to
consist predominantly of non-accessible cross-sections.
It is apparent from ATV documents that some 80% of
public sewers have a nominal size < DN 800. In Berlin,
where approximately 77% of the sewer sections are part
of the separate system, the proportion of nominal sizes
≤ DN 800 even reaches about 90%.
Private sewage systems in Germany, principally estate
drains and house-connection sewers, are between
700,000 and 1,000,000 km in length. The small nominal
sizes predominate here.
These figures account for the special interest of operators
in underground construction methods for small and
medium nominal sizes. Such an ”enclosed” construction
method for making non-accessible sewers and
drains can only be attained for the pipe cross-section to
be installed by displacing or removing soil mechanically
and generally requires a system of remote control.
After a phase of subsidised research projects the ”enclosed
construction method for non-accessible sections”
came into increased use in Germany from about
1984 onwards. On the basis of Japanese developments
the Federal Government research funds deployed mainly
in Hamburg provided the requisite impulse for
progress in Germany too. The initial spark set technical
advance in motion.
At the outset remote-controlled and unmanned thrust
boring was initially confined to the nominal sizes between
DN 250 and DN 1,000 which were necessary for
mechanical-engineering reasons and feasible. The designation
”micro-tunnelling” was nevertheless correct.
Technical development of unmanned remote-controlled
thrust boring has however long since become established
beyond DN 1,000 too; the micro-tunnelling
Fig. 1: Growth of micro-tunnelling at BWB
(cumulative curve)
1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
principle has now come to apply up to DN 1,600 and
beyond, so that one may now speak of an unlimited upward
trend. Its advantages in terms of occupational
medicine are sufficient in themselves to sustain this
trend towards even greater nominal sizes. For some
time, however, thrust-boring systems have also been
available which permit micro-tunnelling for nominal size
DN 200 in sufficient length between manholes. To get
round the lexical problems associated with the term ”micro”
for large dimensions too, Worksheet A 125 Pipe
jacking, September 1996 edition, distinguishes therefore
between
– pipe-jacking methods which operate unmanned
and
– pipe-jacking methods which operate manned.
In the European Standard ”Trenchless laying and testing
of drains and sewers” currently in preparation (now in
draft form as pr DIN EN 12889) the term micro-tunnelling
is used for unmanned remote-controlled jacking ≤ 1,000
mm bore, albeit with the supplementary note that, owing
to technical developments, greater nominal sizes can
now also be jacked.
The economic breakthrough in micro-tunnelling in Germany
has been achieved by Berliner Wasserbetriebe
(BWB) with the development of the ”Berlin method” and
”pipe-eating”. Subsidies have been deliberately dispensed
with here; the market has however been constantly
challenged to tender for trenchless installation
methods. Fig. 1 shows the development of micro-tunnelling
in Berlin between 1984 and 1997 as a cumulative
curve. The trend is still upwards. In the last few years
micro-tunnelling’s share in the total length of sewers installed
by BWB has averaged about 50%, in some cases
even more.
While controlled thrust boring of small pipe sections was
not technically feasible attempts were made, especially
in sewage projects with nominal sizes between DN 400
and DN 800 at great depths and below the water table,
to reduce construction costs by other means.
Accessible sections have also been thrust-bored using
compressed air and smaller product pipes meeting operational
needs installed in them. These have been more
cost-effective solutions than constructing sewers in
open trenches with correspondingly expensive sheeting
and soil excavation together with elaborate dewatering.
In the long term – especially for even smaller nominal
sizes – this twin-shell construction has not however
been satisfactory, especially since at the time no other
use could be made of the large void space between the
two pipe sections.

2. The advantages of micro-tunnelling
Pipe-jacking systems are distinguished by a high level of
mechanisation and therefore require substantially less
manual work than conventional open sewer construction.
From the fact that thrust boring is possible with
concentrated rather than linear construction sites as
with open methods derive the many advantages, with in
some cases substantial economic and environmentrelevant
consequences.
The surface is generally disturbed only at the starting,
target and intermediate shafts or by-shafts. Breaking-up
of the road surface and subsequent restoration with the
associated disruption of traffic is thereby minimised.
Previous relaying of other pipes or underground installations
along or close to intersections with open utility
trenches for sewer construction can be reduced. The
starting shaft, normally covered by the thrust-boring
container, guarantees that work is noise-free and independent
of the weather.
Because of local topography there are often hardly any
differences in level between drainage areas; some
sewers must then be laid at greater depths. With open
construction greater depth is thus accompanied not only
by costly trench sheeting but also by substantial soil
excavation. In towns and densely-populated built-up
areas the excavated soil can seldom be accommodated
in the immediate vicinity of the construction sites, which
may give rise to long transport distances with multiple
loading and unloading. Frequently, too, the excavated
soil cannot be put back again if the requisite degree of
compaction in the road base cannot be attained with it.
In many cases neither the broken-up roadway material
nor the excavated soil may be removed for use at the
contractor’s discretion; both may constitute building
waste which must then be conveyed to listed landfill
sites. Appropriate tests with evidence of suitability must
be performed.
Construction of utility trenches is very expensive anyway,
and is made even more so by the aforementioned
requirements. Calculation of the cost shares for constructing
12,252 metres of DN 200 and DN 250 sewers
in 14 construction projects in Berlin-Heiligensee and
Tegelort in 1983 and 1984 at a figure of about DM 9.2
million (excl. VAT) showed that, taken together, lining
such trenches, excavating and transporting the soil, any
necessary soil replacement, landfill charges incurred,
backfilling and compacting the trench and removing the
sheeting made up some 39% of the construction costs.
About another 31% must go on breaking up and eventually
restoring the road (Fig. 2). This means that,
cumulatively, some 70% of the costs incurred in open
construction have nothing to do with sewer installation
proper and are thus economically questionable.
■
■
■
■
■
■
■
■
■
■
■
39 %
6 %
63 %
Micro-tunnelling Page 7
Fig. 2: Cost shares for DN 200 and DN 250 domestic/industrial
sewer construction by open method
3 % Site equipment
8 %
14 %
31 %
7 %
31 % Breaking up and restoring road
8 %
3 %
12 %
39 % Sheeting, bridges, excavating and replacing
soil, backfilling
8 % Dewatering
7 % Manholes
12 % Sewers, junctions and laterals
Fig. 3: Cost shares for DN 200 and DN 250 domestic/industrial
sewer construction by enclosed method
9 % Site equipment
8 % Breaking up and restoring road
9 %
14 % Sheeting, bridges, excavating and replacing
soil, backfilling
6 % Dewatering
63 % Sewers, junctions and laterals

Page 8 Micro-tunnelling
Quite different cost relativities arise for the examples cited
if sewers are constructed by a trenchless method.
Interference with surface fixings is confined to the small
number of shafts required for thrust boring. If cylindrical
cross-sections are used, the area needed for these
shafts is even smaller than when rectangular trenches
are made for standard manholes leading into the sewers
in accordance with the requirements of DIN 4124.
Trenchless construction methods enable the cost share
of about 31% in the projects referred to above for breaking
up and restoring the road to be reduced to about 8%
(Fig. 3). Shafts not being worked at or in are temporarily
covered using precast slabs (Fig. 4) and are thus not
an obstacle to traffic flow.
Micro-tunnelling ensures high-quality construction. The
jacking pipes have extremely low tolerances. They are
top-quality products and have a reliably long service life,
since they must withstand the special requirements and
stress levels of thrust boring. Thrust boring gives rise to
a largely undisturbed pipe support, and the machinery’s
sophisticated control technology guarantees more precise
routing than in conventional sewer construction.
Micro-tunnelling also offers new approaches to overall
planning of drainage areas. Underground sewers are
made more expensive when installed at greater depths
almost exclusively by the manhole structures, the actual
thrust-boring costs being relatively independent of
depth. The examples examined in the following observations
on cost-effectiveness substantiate this. For
overall planning the result is that drainage areas are less
affected by local topography. They can be enlarged by
placing sewers deeper and simultaneously dispensing
Fig. 4: Thrust-boring site with
temporarily covered starting
and target shafts
with pumping stations. Savings can be effected by this
dispensing with the construction and operation of such
pumping stations.
Moreover, micro-tunnelling brings other economic, safety
and ecological benefits:
The ability of thrust-boring systems to function in
groundwater enables dewatering to be dispensed with
or confined to pumping-out of starting and target shafts
sealed with an underwater concrete bedding proof
against buoyancy.
Frequent causes of accidents in sewer construction are
flaws and faults in the sheeting of open trenches or pits.
In thrust boring, the starting and target shafts, which
generally consist of prefabricated reinforced concrete
shafts or liner-plates, constitute completely safe working
areas for the workers. On micro-tunnelling construction
sites there has to date been not a single serious accident
in Berlin. Adjacent structures been not been damaged,
nor have road users been harmed in the vicinity of the
few open shafts.
Only micro-tunnelling makes simultaneous construction
work feasible in all roads traversing a drainage area,
since sufficient access for fire-engines and other emergency
vehicles can always be guaranteed.
Substantial ecological benefits result from reduced pollutant
emission levels, limited disruption/diversion of
traffic and from sparing grassed areas and trees, which
can be harmlessly under-crossed.

3. Micro-tunnelling: methods
ATV A 125 describes the currently practised methods of
micro-tunnelling for unmanned pipe jacking.
Non-controllable methods
and
controllable methods are distinguished.
Because of the high requirements with respect to positional
accuracy, under ATV A 125 Section 5 only controllable
methods should be employed for thrust-boring
sewers and drains. The figures shown below for maximum
deviations in mm from the specified position (Table
11 in A 125) should not be exceeded.
DN vertical horizontal
600 20 25
600 bis 1000 25 40
1000 bis 1400 30 100
1400 50 200
Max. deviation in mm from specified position for
sewers and drains
3.1 Non-controllable methods
In constructing lareral sewers non-controllable horizontal
thrust borers, used mainly for nominal size DN 150
and limited jacking distances, are also employed. Given
favourable local conditions and appropriate gradients,
jacking distances below 20 metres are possible.
The horizontal thrust borer advances a steel casing tube,
the ground being simultaneously broken down mechanically
at the face by the cutting head and the extracted
soil conveyed by augers (Fig. 5). The horizontal thrust
borer is installed and braced precisely with respect to
level and direction in the starting shaft. When the target
shaft has been reached and the augers retracted the
steel casing tubes are pressed into the target shaft and
there removed, allowing an adaptor holding product
pipes of the same bore being inserted.
It sometimes happens that the location for the target
shaft on the plot to be connected is for various reasons
not yet available. To avoid the necessity for intermediate
shafts in or close to the pavement in front of the plot, socalled
blind shafts have been developed. As soon as the
horizontal thrust borer reaches the target for the advance,
the augers with cutting head are retracted and
the product pipes inserted into the steel casing tubes
Micro-tunnelling Page 9
with stopped ends. Then, while the product pipes are
retained, the steel casing tubes are retracted to the starting
access shaft (Fig. 6). With careful matching the void
formed between steel and product pipe can be kept so
small that any setting is negligible; neither, because of
their greater wall thickness, are any problems caused for
the jacking pipes by the absence of lateral support.
Sizeable voids should however be filled.
The blind boring, providing the means of underground
connection to existing collectors ≥ DN 300 or shafts,
was developed some years ago by Bohrtec. Here, in addition
to the horizontal thrust borer, a drill rod, diamond
bit and special sealing element are needed. Once the
thrust borer has reached the collector or shaft, augers
and cutting head are retracted and the drill rod with diamond
bit inserted. Drilling into the collector is monitored
from inside by television camera. There the drill core too
Starting shaft
1. Boring
Fig. 5: Non-controllable horizontal thrust boring
Steel casing tube
Thrust borer Screw conveyor
2. After-pushing of product pipes
Starting access hole
1. Boring
Cutting head
Product pipe
(jacking pipe)
Steel casing tube
Steel casing tube
Adaptor
Drill head
Thrust borer Screw conveyor
Product pipe
Steel casing tube
2. Insertion of product pipes
Retaining assembly
Stopper
3. Retraction of steel casing tubes
Target shaft
Fig. 6: Non-controllable
horizontal thrust boring:
making a blind hole

Fig. 7: Non-controllable
horizontal
thrust boring:
blind hole with
underground
connection to a
collector
Page 10 Micro-tunnelling
is removed. The lateral sewer made of DN 150 vitrified
clay pipes is then drawn in. At the point of this rod is the
special sealing element, which ensures proper connection
of the product pipe to the collector. The steel casing
tubes are then retracted and the void surrounding the
product pipes filled with a special slag (Fig. 7).
An alternative method of non-controlled thrust boring is
underground drilling from a ≥ DN 1200 collector. A trolley
can be brought to any drilling point in the collector
and be set to the required angle of incline up to 90˚. Using
adaptor and diamond bit, the collector is then bored
through to the required external diameter. Subsequent
drilling through the ground is performed with steel
Starting shaft
1. Boring
2. Collaring
casing tube and augers. When the thrust-bore target is
reached, the augers are retrieved and the underground
wall or inspection chamber drilled through with drill pipe
and diamond bit. Finally the product pipe is inserted and
the steel casing tube retracted while the product pipe is
Fig. 8: Non-controllable horizontal
thrust-boring: boring from
a ≥ DN 1200 collector
Steel casing tube
Cutting head
Thrust borer Screw conveyor
3. Insertion of product pipes
with special sealing element
4. Retraction of steel casing tubes
Collector
Pipe Ø DN 1200 mm upwards
retained. If there is adequate working space in the
thrust-bore target, the product pipes can alternatively be
pushed through afterwards and the steel casing tubes
removed at the target (Fig. 8).
3.2 Controllable methods
For constructing sewers and drains three thrust-boring
methods in particular have come to predominate in
practice:
pilot pipe jacking and
thrust boring using steel joint heads and mechanical
or hydraulic soil transport (auger orslurry conveying).
Pilot pipe jacking
In this process a steel pilot pipe, hollow and therefore
having an optical channel, in sections normally of 100
cm length and with an external diameter of about 10 cm
is driven from a starting shaft to a target hole, compressing
the soil. Directional accuracy is normally
monitored by means of a theodolite with CCD camera
located in the starting shaft and a diode panel fitted in
the optical channel in the first pilot pipe. The position of
the externally tapered first pilot drill pipe is continuously
transmitted to a monitor in the starting shaft. If it deviates
from the specified axis, the pilot drill rod is turned
so that the angled head at the point of the string brings
about a directional correction as it is further advanced.
Accurate arrival of the pilot drill rod in the target shaft
and its recovery there rod by rod are followed by an
adaptor widening the cross-section to accommodate
steel casing tubes with augers. The soil is conveyed to
the starting shaft. When the steel tubes have reached
the target shaft, the augers are retracted, an adaptor is
inserted, the product pipes are pushed in behind and the
steel casing tubes are recovered in the target shaft (Fig.
9). Fig 10 shows the final phase of pilot pipe jacking using
DN 150 vitrified-clay pipes.
This method has proved itself over years for installing
house connections up to 20 (max. 30) metres long. In
loosely bedded soils without embedded rock two-phase
application, i.e. without steel casing tube, is also sometimes
practised.
Numerous improvements in detail, especially in the
coupling for the pilot pipes, have enabled this technique
to be used for about two years now also for underground
laying of DN 200 and DN 250 sewers with the section
lengths normal in sewage systems. Like all pilot pipe
jacking, however, this technique requires displaceable
soil without substantial embedded obstacles. The pilot
drill pipe has recently also become available in watertight
form, so that with a modified screw-conveying

Fig. 9: Pilot pipe jacking
system work below the water table is now also possible.
The thrust boring of DN 200 sewers in section lengths
which is now feasible is acquiring pre-eminent importance.
The accurate underground driving of sewers of
this nominal size at the customary section lengths was
not possible earlier with the thrust-boring systems
available on the market. From the inception of microtunnelling
the conveying equipment to be incorporated
inside the jacking pipe for moving the displaced soil, including
protective tubing for cables, and the essential
optical channel for the laser beam to control the advance
determined nominal size DN 250 as the smallest crosssection
of access-hole length drivable underground. For
operators this meant that for constructing collectors
they had to dispense with the customary smallest nominal
size DN 200 if on economic grounds or because of
compelling local factors enclosed construction methods
had to be preferred to conventional sewer construction.
Fig. 10: Pilot pipe jacking, final
phase: after-pushing of the vitrified-clay
pipe from a DN 2000
starting shaft
How widespread DN 200 is in the public sewage systems
is shown by figures from the BWB’s combined and
domestic/industrial sewage systems: some 32% of the
BWB’s 8613-km long sewage system is of this nominal
size. Particularly in the separate systems’ domestic/industrial
sewage networks large parts of the drainage areas
can be developed with DN 200 circular cross-sections
and are hydraulically fully adequate for all operational
requirements. If one considers the Berlin domestic/industrial
sewage networks alone, DN 200’s share is
as much as 65%. Because of this special importance
operators have never abandoned the desire and requirement
to be able one day, with improved technology, for
controlled driving of DN 200 pipes too. This has now
been made possible by the work of three German machinery
producers in particular and provides planners
and operators with other alternatives and the means of
investing more economically since sewer construction is
becoming more cost-effective.
The requirements of ATV A 125, Section 6.2.2 governing
the measuring and logging of runs of piping in the construction
of jacking systems are met. During the jacking
process, for example, the image on the monitor in the
starting shaft can be continuously recorded by a videorecorder.
All possible deviations are thus registered.
Moreover, when product pipes are installed, the jacking
pressure can be recorded by a pressure transducer with
a memory by a recording manometer of the peak value
in the measurement period.
Thrust-bore pipe jacking
Micro-tunnelling Page 11
Here the product pipes are advanced at the same time
as soil is displaced at the face by a cutting head. The
soil is continuously conveyed to the starting shaft by
augers. The augers are in a steel tube inside the jacking
pipe. With each installed pipe the auger and pipe string
is lengthened. The conveying pipes have skids and, like
the augers, are adapted to the bore of the particular pipe
to be jacked.
In the starting shaft the soil is collected in a steel bucket
during a jacking period and conveyed to the surface
during the coupling operation. In this way the quantity
of soil actually removed at the face is reliably monitored.
An alternative to bucket extraction is to set up a sump in
the starting shaft and convey by pumping. Fig. 11
shows a thrust-boring container with a Soltau thrustbore
pipe jacking system.
Cutting head and augers are normally driven from the
starting shaft. For heavy soils it is necessary to have
available consistently high torque to comminute the
drilled matter effectively. From DN 400 upwards pipejacking
machines are therefore also offered with directly
driven cutting head and separately driven augers.

Page 12 Micro-tunnelling
Elements in the control system are the electronic target
panel, the jacking laser and the hydraulically pivoted
steel joint head with three control jacks. The laser unit is
installed in the starting shaft independently of the abutment.
This is very important, so that the laser’s alignment
is not altered during thrust boring by movements of
the abutment. For the same reason special care must be
applied to making starting shafts or trenches stable and
stationary. The laser beam gauged to the target shaft
marks the planned position for the sewer. It strikes the
electronic target panel fitted in the machine pipe (following
the steel joint head), the so-called ”target”. The coordinates
of the laser reception point and the roll and
inclination of the control head are measured and the
values transmitted to a display panel on the control
console. The measured parameters are ultimately
converted by a computer into control commands for the
control jacks. These control actions take place automatically
in short jacking periods, but can also be transmitted
manually. A measurement log with all recorded
parameters can be printed out for any period of time or
distance. This also applies to the shield-jacking operations
described below. Fig. 12 shows a log for such a
thrust boring using a Herrenknecht AVN 700 shield jacking
machine.
Fig. 11: Thrust-bore
pipe-jacking site on a
public road
Column 1: Dates
Column 2: Time
Column 3: Station in mm
Column 4: Laser vertical in mm
Column 5: Laser horizontal in mm
Column 6: Rotaty cutter vertical in mm
Column 7: Rotaty cutter horizontal in mm
Column 8: Nick (slope) in mm/m
Column 9: Gier (bearing) in mm/m
Column 10: Roll in degrees
Column 11: Torque in bar
Column 12: Pressure in to
Column 13: Cylinder left (Position) in mm
Column 14: Cylinder upper (Position) in mm
Column 15: Cylinder right (Position) in mm
Column 16: Temperature in target panel in °C
Column 17: Reference voltage (Target panel) in Volts
Column 18: Zero voltage (Target panel voltage) in Volts
Column 19: Laser amplitude (Target panel) in %
Column 20: Laser diameter (Target panel) in mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21.6.94 17:27:39 0,10 8 -1 -6 6 -1,3 -3,2 -1,2 102 3,0 0 0 0 28 3 0 1511 16
21.6.94 17:49:02 0,20 9 -1 -4 8 -2,6 -4,9 -1,5 167 3,6 0 0 0 30 3 0 1451 18
21.6.94 17:49:40 0,30 9 -1 -3 8 -3,3 -3,9 -1,3 132 2,5 0 0 0 30 3 0 1451 17
21.6.94 17:51:10 0,40 8 -1 -3 8 -3,1 -2,9 -1,3 140 3,0 0 0 0 30 3 0 1491 19
21.6.94 17:54:04 0,50 7 -3 -1 5 -5,2 -2,0 -1,5 174 4,1 0 0 0 30 3 0 1571 16
21.6.94 17:54:08 0,60 6 -3 -1 3 -6,0 -2,0 -1,4 196 5,1 0 0 1 30 3 0 1591 15
21.6.94 17:54:17 0,70 8 -3 -5 3 -7,7 -2,6 -1,5 152 3,1 0 0 1 30 3 0 1551 14
Fig. 12: Specimen thrust-bore log

The application range generally covers nominal sizes
between DN 200 and DN 1000 and jacking distances up
to max. 100 metres in unconsolidated material. In cohesive
soils of firm consistency extraction and conveying
of the soil can be facilitated by adding water at the face.
In water-bearing soils supplementary measures are
necessary. For use in groundwater up to max. 1.50 but
not more than 2.50 metres the face can be stabilised
with compressed air. The first conveying pipes are for
example fitted with modified augers with a shorter lead,
so that soil plugs form which prevent the compressed air
from escaping. Another possibility is to provide the
starting and target shafts with locks and operate with
compressed air. For this purpose a combined personnel
and materials lock has proved effective which enables
persons and materials to be got into the working area in
separate pressurised chambers. The control console is
installed over the jacking machine and outside the compressed-air
chambers, so that working under atmospheric
conditions is possible here. This compressed-air
alternative is very costly and reserved for special cases.
The method does however have two advantages: firstly,
conveying with augers makes the separation system redundant,
so that no special action is required in severe
frost. Secondly, any recovery necessary at the face of
obstacles to thrust boring and associated operations on
the control head are possible with the compressed-air
equipment available at the site, without need for elaborate
dewatering.
In view of the very successful two-/three-stage jacking
systems using pilot rods and expansion boring in constructing
house connections and nominal sizes for
smaller collectors up to DN 400 a new thrust-bore pipe
jacking system, first demonstrated by Bohrtec at Bauma
’98, should be mentioned.
It is based on two-phase thrust boring and is in initialcost
terms an economical alternative to thrust-bore pipe
jacking used hitherto to install sewers of nominal sizes
between DN 400 and DN 800.
In the first stage of the process a steel casing tube of external
diameter 420 mm with internally fitted augers is
jacked from a starting shaft with unobstructed width 320
cm up to max. 60 metres to a target shaft. The augers
have – like the pilot pipes – a hollow axis and, at the
point of the screw line, a taper. Depending on the position
of this oblique plane relative to the soil at the face,
control movements can be executed during jacking.
This principle of the so-called ”controlled auger” permits
soil conveying also to be optimised with respect to embedded
stone, since the entire cross-section of the steel
casing tube is available for the purpose; the optical
channel runs in the hollow axis of the revolving auger
line, no longer above a separate conveying pipe in the
clearance from the casing tube. Directional accuracy is
again monitored by means of a theodolite with CCD
camera and the monitor in the starting shaft and of the
diode target panel in the control screw. The first stage in
the process is carried out with the same equipment for
all nominal sizes to be jacked and uses a clockwise-rotating
screw line to transport the soil. When the control
auger and first casing tube arrive at the target shaft, the
second stage begins: an expansion stage with directly
driven cutting head is docked on to the end of the line of
steel tubes and, now turning anti-clockwise, conveys the
soil encountered through the steel tube line of the first
process stage to the target shaft. The size of the expansion
stage depends on the nominal size of the
product pipes (Fig. 13).
Shield pipe jacking
Micro-tunnelling Page 13
Fig. 13: Two-phase thrust boring with control
screw, augers and expansion stage, rotating
clockwise and anti-clockwise
Here thrust boring of the product pipes is accompanied
by simultaneous all-over soil removal at the mechanically
and fluid-assisted face by a directly driven cutting
head which is rotating both clockwise and anticlockwise.
In contrast to the machines using auger conveying, with
slurry-conveying machines the soil is transported by a
closed fluid circuit. As a rule the conveying medium
used is water. For loosely bedded, non-cohesive unconsolidated
material use of a bentonite suspension to
prevent uncontrolled soil removal is appropriate. This
type of machine thus lends itself well to coarse-grained
soil types at any groundwater level.
To operate the slurry system a feed pump, normally installed
at ground level, and suction pump in the starting
shaft are needed. By appropriately controlling the two
pumps any pressure required at the face can be set and
thus any water pressure counteracted. Crushers are incorporated
in all slurry systems, so that extracted material
is comminuted to an extent which ensures its subsequent
blockage-free transport through the conveyor

Page 14 Micro-tunnelling
pipe. Used in conjunction with suitable stoping tools,
slurry systems lend themselves to working through even
major obstacles, provided that such obstacles are firmly
bedded in the soil and the angle of impact causes no deflection
of the cutting head. If the cutting head is fitted
with roller bits, thrust boring is possible even in hard rock
and especially heavy soils (Fig. 14).
Fig. 14: DN 800 rock
cutting head with
roller bits
Fig. 15: Rear view of
an AVN 800
with target and
supply pipes (Herrenknecht)
The control technology is generally no different from that
of thrust-bore pipe jacking described earlier. The range
of application extends from DN 200 to far into the range
of manned advances and accordingly also – depending
on nominal size – to jacking distances up to several hundred
metres. Fig. 15 shows the rear view of a Herrenknecht
AVN 800 with target and supply pipes.
All the micro-tunnelling systems mentioned are designed
for low operating costs. For carrying out thrust boring
alone three to four workers suffice. The extent of site
equipment is not great and the equipment for the thrustboring
process can be installed in relatively small
starting shafts. Compact construction permits the machines
including all units to be accommodated in steel
containers suitable for on-site use. They are set up as
static units with a bottom opening over the starting
shaft. The container design not only optimises the
space requirement, but also enables construction to proceed
regardless of weather conditions. In Berlin thrustbore
pipe jacking has been carried out from heated containers
down to –20˚C. Open-method pipe laying, as is
well known, becomes impossible in even slightly sub-zero
temperatures and frozen ground. Companies with
jacking equipment can therefore earn at normally income-less
times of year. In so doing they promote yearround
working in the construction industry and contribute
to relieving the employment market.
Fig. 16: Soltau mobile thrustboring
unit
As an alternative to static thrust bore containers mobile
units are also available in which the construction gear is
mounted on a trailer gantry. This permits rapid movement
between sites without low-loaders and makes
micro-tunnelling solutions economic even for short jacking
distances and small sites. In this version diesel
generating sets provide complete independence from
the public electricity mains (Fig. 16).

4. Selection criteria for jacking
systems
As soon as different systems are available on the market
the question of which it is advisable to use for which
purpose arises. There is no single answer to this
question since all systems have both advantages and
disadvantages, the scope for use is wide and the constraints
in problem definitions are often very complex.
It is important that the promoter/client provides potential
contractors with not only a comprehensively documented
unambiguous plan but also, specifically, the most
exact possible and sufficient data on the geology and
soil mechanics of the line to be followed by the sewer
and on the groundwater conditions. The decision on the
jacking system to be used should – for purposes of
rational spreading of risks – ultimately be left to the
bidder, i.e. the subsequent construction company.
Capital outlay for thrust-bore pipe-jacking systems is
lower. They need less space and personnel, yielding
time saving of up to 35% over shield jacking systems for
setting-up the site.
The following two tables analysing advance rates
attained, including set-up time, yield further information.
The first comparison shows a distinct decline in average
advance rates for thrust-bore pipe-jacking systems as
nominal size increases. For > DN 500 they drop to about
66% / 71% of the rates attained for DN 250.
In contrast, with shield pipe jacking, i.e. with hydraulic
conveying, advance rates including set-up time are
found to be more-or-less independent of nominal size.
BWB: thrust-bore pipe jacking, average
advance per 8 hours in metres
Advance Advance
with set-up time
DN 250 9,93 6,08
DN 300 8,61 5,20
DN 400 8,32 4,91
DN 500 8,46 5,00
>DN 500 6,58 4,34
The analyses relate to approximately 167,000 metres’
total advance up to the end of 1994 in Berlin. It should
be noted that the figures naturally reflect all local
constraints, but also the skill and motivation of the personnel
on site and the whole ethos of the executing
company.
Micro-tunnelling Page 15
BWB: Shield pipe jacking, average advance
per 8 hours in metres
Advance Advance
with set-up time
DN 250 10,83 6,19
DN 300 9,82 5,41
DN 400 11,22 6,52
DN 500 11,91 6,69
DN 600 10,82 6,30
DN 800 11,01 6,00
DN 1000 11,65 6,71
DN 1200 11,99 7,23
The trend towards distinctly higher rates with shield pipe
jacking systems at nominal sizes DN 400 is however
conspicuous. This is partly due to the fact that at larger
nominal sizes continuous transport of soil by flush-conveying
is clearly superior to that using buckets. Moreover,
the higher extraction and comminution rate has
particularly beneficial effects where the ground is difficult.
The constantly direct drive of the cutting head, the
smaller losses compared with auger drive and the possibility
thus afforded of driving greater lengths also make
themselves felt in favour of auger systems.
Selection of a jacking system with the particular
extracting tools needed is however most strongly
influenced by the geological conditions and groundwater
level. See in this connection a publication by W. Becker
(Berlin) on ”Scope and limits of micro-tunnelling taking
extraction tools into account” (offprint from the journal
”Tiefbau” , Vol. 7/1996, obtainable from Steinzeug
GmbH, Max-Planck-Strasse 6, 50858 Cologne). Taking
as its basis the soil classifications of the General Technical
Contract Terms (ATV), DIN 18319, VOB Part C, this
article makes recommendations on selecting suitable
jacking systems.
5. Micro-tunnelling applications
With the jacking systems available on the market construction
orders for all nominal sizes used in sewage
systems for both extension and renewal purposes are
possible. Oval cross-sections too, which are enjoying
something of a renaissance in waste-water engineering
by virtue of their hydraulic advantages, can be jacked
underground. Their external profile must of course have
a circular cross-section, and precise adherence to the
pipeline invert must be ensured. This requires roll-free
jacking, which can be achieved if adjacent pipes are
joined with shearing pins and machines with flush-conveying
and thus cutting heads rotating clockwise and
anti-clockwise are used.

Page 16 Micro-tunnelling
The following tasks can be handled:
– Underground making of connecting drains and house
connections as blind-hole borings or with starting and
target shafts. The starting shaft may be either above
the collector or on the plot.
– Underground making of house connections with
underground connection to collectors.
– Underground installation of sewers to extend sewage
systems.
– Underground installation of sewers and house connections
by a cyclical method (the Berlin method).
– Replacement of sewers by underground construction.
Until the changeover the old sewers serve to keep the
system operating. The Berlin method can also be applied
to sewers and house connections in need of
replacement, possibly in conjunction with pipe eating.
– Underground replacement of sewers by replacing
damaged sections (pipe eating).
– Underground cutting of a sewer no longer needed in
its original cross-section and previously filled with
packing.
5.1 The Berlin method
The starting point was the concern to reduce digging-up
of the road. If thrust boring is decided on only when the
public sewer is constructed, while the house connections
it serves are made by the open method, the result
is a perforation of the surface vertical to the road axis for
every single connection. In the light of today’s technical
possibilities such a procedure is inadequate. A remedy
is provided by the Berlin method, which comprises
consistent application of controlled pipe jacking for collectors
and feeder-sewers in a cyclical process (Fig. 17).
In it for nominal sizes ≤ DN 800 prefabricated cylindrical
starting and target shafts with internal diameter 2000 /
3200 mm and jacking pipes with nominal length 1000
and 2000 mm are used. Fig. 18 shows a 3.20-metre
wide starting shaft with shield pipe jacking of DN 500 vitrified-clay
pipes.
Fig. 17: The Berlin method
Berliner Wasserbetriebe
Drainage Network Dept.

Fig. 18: Starting shaft
(3.20 metres) with shield jacking
of DN 500 vitrified-clay pipes
For nominal sizes greater than DN 800 rectangular shafts
must generally be dug. Alternatives for all nominal sizes
are starting shafts of reinforced shotcrete, which lend
themselves well to confined spaces, or the ONE-PASS
SHAFT LININGS from England. The latter are prefabricated
concrete tubbings which can be assembled on
site, are available in a variety of bores from 1.52 to 10.67
metres and are reusable.
The shafts needed for thrust boring road sewers are also
the starting point for thrust boring house connections,
which are thrust bored to the plots in a radial way. If the
shafts are arranged carefully according to local conditions,
several plots can be reached from one shaft without
any overlength arising for the particular house connection
or need to tunnel under other plots.
In the Berlin method type I the plots which cannot be
reached from the starting or target shafts are
accessed – also radially – from sunk ”by-shafts”. In the
by-shaft the feeder-sewers are linked to the collector by
backdrops and fittings. If the collector is above the
groundwater, the by-shaft is sunk using liner-plate rings
after thrust boring of the collector has been completed
and retracted for re-use when the house connections
have been constructed (Fig. 19). If the collector is in the
groundwater, prefabricated reinforced-steel shafts are
used for the by-shafts and sunk before any thrust boring
starts. Like the starting and target shafts, they are
sealed watertight under pressure under the sewer bottom
with an concrete seal preventing buoyancy.
Micro-tunnelling Page 17
Pipe jacking then takes place through prepared apertures
with collar seals against the pressing groundwater
from the starting to the target shaft, through the byshafts
which remain in the soil (Fig. 20). In the final cycle
the starting and target shafts are finished as manholes
with the usual dimensions.
In the Berlin method type II the ”by-shafts” are replaced
by additional starting, target or intermediate shafts
linked radially to the house connections; when construction
is completed, these become ordinary manholes into
the sewer system (Fig. 17). This version meets the requirement
in ATV A 142 that in Protected Zone II waterprocurement
areas all feeder-sewers must be -connected
to access-hole structures.
The usual alternatives for finishing/converting the
starting, target and intermediate shafts as/to ordinary
manholes into the sewers are evident from Fig. 17 in
conjunction with the diagrams in Fig. 21 to 23.
Fig. 19: Berlin method: by-shaft above groundwater table

Fig. 20: Berlin method: by-shaft below groundwater table Fig. 21: Berlin method: starting/target shaft finished as manhole
Fig. 22: Berlin method: starting / target shaft with manhole (concrete polymer) Fig. 23: Berlin method: starting / target shaft with manhole (DIN 4034 concrete)

Fig. 24:
Pipe eating
In addition to the shaft-to-shaft alternative other solutions
are conceivable. There is a broad field here which
should be exploited by innovative and complex solutions
taking account of subsequent use, since manhole
structures remain – and especially so in thrust boring –
relatively high-cost facilities in which further savings
must surely be possible.
Radiating thrust boring of the connecting sewers and
bringing them into the manholes permits the lowest possible
depth, mostly above the water table. On the other
hand, backdrops in the manhole are necessary, which
however permit changes in the direction of flow and thus
ensure hydraulically sound connection of drains arriving
at acute angles to the collector’s direction of flow.
In addition to the economic advantages, bringing feeder
sewers close to manholes also has a number of operational
ones, in particular because there are openings at
both ends of the pipe, facilitating cleaning and inspection.
Because sealing is technically straightforward, water-permeability
tests can be performed rapidly and reliably.
A feeder-sewer constructed in this way can later
be straightforwardly rehabilitated by re-lining. Another
advantage is that the composition of the sewage from
each plot can be separately checked. There are moreover
no fittings in the sewer section: this means less incidence
of damage in the future, since surveys of the
sewage system currently show that most damage occurs
at junctions within the section.
5.2 Pipe eating
Initial successes with micro-tunnelling in Germany immediately
prompted the thought that this technique
might also be applied for replacements in the line of the
old sewer, i.e. sewers needing replacement could be
overlaid with new jacking pipes. This technique makes
it unnecessary to search for a line for the sewer in the
cross-section of roads already carrying much. At the
same time a larger, more capacious sewer cross-section
is obtained, a need which applies to many old sewers.
An advantage over many other sanitation methods is
Micro-tunnelling Page 19
moreover that overlaying yields a high-quality new sewer
with correspondingly long service life. The joint interests
of operators, contractors and machine builders led
to the following technical development of ”pipe eating”:
– The basic features of thrust-boring and shield pipejacking
machines remain; the steel joint heads and
extracting tools are modified for the new task. Both
auger and slurry conveying is suitable. In order not to
interrupt the flush-conveying circulation the sewer to
be replaced must either first be filled or a sealing
packing system sent ahead of the cutter head.
– All unreinforced sewer or pipe materials can be
crushed and removed via the conveying system.
– It is possible to use any commercially available
jacking pipes.
– The excentric pipe jacking needed for maintaining the
invert incorporation of individual sewer sections in
need of replacement and lateral and vertical alterations
to the sewer position as found are made -possible
by precise controllability.
To facilitate fault-free construction and be able to lay a
high-quality new sewer, the following preparations for
pipe eating must be conscientiously carried out:
Before pipe eating starts the existing junctions are cut
off and the waste water present pumped over using
lifting equipment. Discharge over a sewer section to be
replaced must also be maintained by appropriate
by-pass pipes or temporary diversions.
Of particular importance is a preliminary clear-cut survey
to detect any tilting in the sewer to be replaced, so that
the new sewer cross-section receives proper support. If
tilting is excessive, special measures must be taken. A
larger pipe cross-section can for example be driven, or
laying the whole section deeper or localised backfilling
considered. The prior sewer survey must include the
feeder-sewers. If their condition is still good, they can
be reconnected later at the same point. If however the
connecting sewers must also be replaced, pipe eating in
conjunction with the Berlin method is available, i.e. radial
connection to the shafts. Fig. 24 shows a pipe-eating
operation in Berlin; here an approximately 100-year-old
vitrified-clay DN 180 section is being replaced invertconform
with DN 250 vitrified-clay jacking pipes.
A higher level of wear, a slower rate of advance and
expenditure on maintaining discharge for house connections
and parts of the system above the installation site
make pipe eating more expensive than normal pipe
jacking. In replacement projects it is therefore generally
more cost-effective – provided there is a free line available
in the road’s cross-section – to drive a new sewer
there and use the old one for temporary maintenance of

[m]
8.000
7.000
6.000
5.000
4.000
3.000
2.000
1.000
Page 20 Micro-tunnelling
discharge. Given the ever more confined underground
space in conurbations and on industrial sites and for
special applications, however, pipe eating has now
become indispensable. Fig. 25 gives information about
the frequency with which pipe eating has been employed
at BWB in comparison with laying of replacements.
BWB – Micro-tunnelling: Replacement methods compared
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
■ replacement laid in new position
■ pipe-eating
Fig. 25: Laying of replacements and
pipe eating compared
6. Planning and preparatory
construction work
Planning, design, tendering, preparatory construction
work, execution and settlement of accounts for pipe
jacking are governed by the general Standards and by
the following special technical Standards, which must be
complied with:
– ATV Worksheet A 125 Pipe jacking, September 1996
– ATV Worksheet A 161 Stress analysis of jacking pipes,
January 1990
– Standard rating books for the construction industry,
rating range 085 pipe jacking, March 1997
– DIN 18319 General technical contract terms for pipe
jacking, VOB, Part C June 1996
Additionally, account must be taken of the relevant quality
and testing regulations of April 1998 of Quality Safeguarding
in Sewer Construction (”Association for Quality
in Sewer and Drain Construction and Maintenance”).
6.1 ATV Worksheet A 125 Pipe jacking
A guide for specialists working in planning and execution
is ATV Worksheet A 125 Pipe jacking already cited
several times. In two sections it describes all unmanned
and manned pipe-jacking methods and their range of
application. In the section on structures and machinery,
jacking pipes & joint assemblies and shafts specific requirements
made of jacking pipes of all materials and
their joint assemblies are formulated in a technical Standard
for the first time. Especially important here are the
permitted tolerances for pipes with respect to nominal
length, rectangularity of pipe ends, deviations from
straightness, external pipe diameter and invert conformity.
The general requirements for joint assemblies
relate to, amongst other things, impermeability, deflection,
resistance to shear force, transmission of longitudinal
forces and sealing of gaps. The aim is to take these
requirements of jacking pipes into account in relevant future
materials standards. With EN 295-7 Vitrified-clay
pipes and fittings, joint assemblies for sewers and
drains, Part 7: Requirements made of vitrified-clay pipes
and joints in pipe jacking, German edition DIN EN 295-7:
1993, now introduced in all member countries, this has
already happened very early in parallel with work on
A 125 and even at European level.
[m]
60.000
50.000
40.000
30.000
20.000
10.000
BWB – Micro-tunnelling: Relative quantities of materials in jacking
pipes
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
■ fibre cement ■ vitrified clay
■ reinforced concrete ■ other
Fig. 26: Relative quantities
of materials in jacking pipes
compared

Fig. 26 shows the relative quantities of materials in the
jacking pipes used by BWB in Berlin.
A section on preparatory planning includes amongst
other things the maximum deviations from the specified
position and requirements made for assessment of all
existing structures and installations, subsoil and groundwater
conditions and data on settings. The declaration
of preferred nominal sizes is intended to support the
rationalisation already brought about in the market with
respect to limiting the number of jacking heads but also
to stock-keeping of pipes. The section on execution
calls for specialist companies and jacking logs with the
parameters relevant to individual jacking operations.
Additionally, extraction and conveying of soil, entries
and exits, pumps, supporting and sliding means are
treated. Special sections include the specific requirements
for jacking under Deutsche Bundesbahn AG
track, under federal highways and waterways. References
facilitate the search for further standards and
regulations.
6.2 ATV Worksheet A 161 Stress analysis of
jacking pipes
Worksheet A 161 spells out what loads are to be considered
for jacking pipes in the different phases and the
procedures for measurement and safety certification. A
distinction must be made between:
construction state: stress in the pipe axis
stress across pipe axis
operating state: stress across pipe axis
demonstration of
fatigue-strength
minimum measurement: stress caused by secondary
bending moment
Pipe producers are generally willing to prepare the stress
analyses for jacking pipes and have for this purpose prepared
forms for their customers on which both the local
constraints and the particular jacking parameters should
be entered.
6.3 Standard rating books, rating range 085
(pipe jacking)
Tender specifications for the standard rating range (pipe
jacking) enable all jacking methods covered in A 125 to
be translated into specific tender specifications. The
standardised texts specify performance so clearly and
exhaustively that prices can be reliably calculated. This
provides at the same time the basis for awarding contracts
for jacking services and settling accounts for them
automatically. The texts meet the requirements of the
VOB and technical standards. With electronic data-processing
the modular structure of the texts of all standard
rating books enable the required text combinations to be
assembled quickly and, additionally, to be exchanged on
data media between clients, consultant engineers and
contractors. This facilitates scrutiny of tenders and
comparison of prices and enables price files holding
average prices to be set up. This is an effective contribution
to rationalising the construction industry which
simplifies the work involved in awarding contracts and
settling accounts and could also lead to an increase in
the acceptability of pipe jacking. Pipe jacking has in the
past often not happened because the agencies concerned
experienced difficulties in formulating specifications
for it. The standard rating book is structured as follows:
– site equipment for pipe jacking
– starting, target and intermediate shafts
– jacking pipes, pipe jacking
– pipe jacking in special fields, allowances for pipe
jacking, safety precautions
– planning of support structure and special equipment
– preservation of evidence
– survey work, as-built plans
– measuring, monitoring points
– documentation
– recycling, disposal
Micro-tunnelling Page 21
6.4 DIN 18319 General Technical Contract
Terms for Pipe Jacking Work
If the VOB are agreed to for a construction contract, any
pipe jacking work arising should be specified in accordance
with the General Technical Contract Terms in Part
C of the VOB (DIN 18319). Their validity covers all the
methods here described. They do not cover earthworks
for making shafts or trenches or removal of soil. Work on
trench sheeting, in connection with pumping and other
pipe laying should also be included separately in the
specification.
The soil classifications reflect the special features of
jacking. There are

Page 22 Micro-tunnelling
– 6 classes for non-cohesive unconsolidated material
63 mm particle size with sand and gravel as main
constituents, according to their compactness (loose,
medium-dense, dense) and particle-size distribution
– 6 classes for cohesive unconsolidated material 63
mm particle size with silt, clay or sand, gravel with
high proportions by mass of silt and clay as main constituents,
according to consistency (slurry-soft, stiffsemi-rigid,
rigid)
– 4 additional classes for unconsolidated material with
particle size > 63 mm, depending on proportion by
mass of the stones and their size
– 8 classes for consolidated rock, depending on its unconfined
compression strength and interfacial spacing
– other materials (e.g. mining waste dumps or under
refuse dumps)
This detailed classification system takes account of the
contractor’s need for precise information about the
ground for selecting the jacking method and costing.
The tender specification for jacking work must include
the following:
Erection and backfilling the starting and target shafts,
supplying the pipe material,
the jacking operations, separated according to nominal
size and soil classes,
recovering obstacles,
keeping jacking logs as required under A 125,
transporting soil away.
6.5 Obstacles
Despite the technical advances in cutting through stone
and breaking it down with integral crushers and in continuous
conveying, an accumulation of unexpected
obstacles always slows thrust boring down. In bad
cases obstacles must moreover be recovered, which
sometimes involves directional adjustment of the control
head at the same time. These are special risks in thrust
boring, which increase in inverse proportion to the
nominal size. Interbedded rock is however also – if the
local compactness permits – either displaced to the side
or pushed along at the face. If large rocks are not
engaged centrally, there is also danger of the control
head being diverted.
There are as yet no reliable methods of locating with sufficient
accuracy at the planning stage rock obstacles for
the defined area of the cross-section to be driven. It is
therefore important to keep on drawing attention to the
fact that for risk-apportionment purposes the project
promoter should be regarded as the owner of the
ground. He must analyse geological maps at the planning
stage and should carry out ”historical searches” on
the local situation. Site surveys must include the requisite
information and parameters for the stress analysis
and jacking listed in A 161 and A 125. The results of
exploratory drilling should be presented as per DIN 4022
as drilling logs and driving diagrams as far as possible in
longitudinal sections through the subsoil. All these
records yield however information which is, strictly
speaking, valid for only one point. Previously undetected
intercalation must however be expected, so that tender
specifications should include statements about the
accounting arrangements. DIN 18319 logically stipulates
that the means by which rocks constituting an obstacle
to jacking operations are to be eliminated must be
specified jointly, i.e. there should be a section in the
specification dealing with recovery of obstacles. The
size of rocks constituting obstacles should be defined in
this section. In Berlin the following procedure has been
found effective:
Trial drillings, driven and/or static soundings and analyses
of them are generally performed at intervals between
50 and 100 metres in the area of the planned line and
form part of the tender specification. Selection of the
jacking system is generally the prerogative of the bidder.
In his tender he must however state the system selected
and define the obstacle size at which crushing and conveying
by the machinery becomes impossible. The
trenches needed for recovering obstacles above this diameter
and the standby costs incurred during recovery
are paid separately. This is effected by the client setting
out on the basis of empirical values a certain number of
recovery trenches of appropriate sizes, depths and
types of sheeting and the contractor then specifying
prices for them. In this way obstacle elimination with
provision of the jacking equipment is made competitive.
Jacking costs can thus be estimated with less risk and it
is easier for the client to examine tenders.
Missing or deficient subsoil surveys in conjunction with
incomplete or absent tender specifications are constantly
leading to problems, breakdowns and disputes in the
course of construction. The result is often that all concerned
are angry and disappointed and quite wrongly
take long-term leave of micro-tunnelling. This is why the
planning, tender-specification and preparatory stages
are more important in enclosed construction methods
than in conventional sewer construction.
As mentioned earlier, jacking of smaller nominal sizes in
obstacle-rich and heavy soils can be problematic. If
economically justifiable relative to other solutions, to reduce
the risk of interruptions the use of a twin-shelled
version is also usual in such cases; first a fairly larger and

high-capacity jacking pipe – e.g. DN 500 – is jacked
using a stronger jacking system and the operationally
necessary smaller piping then accommodated in it.
Alternatively a so-called ”composite pipe” can be used.
It consists of an inner pipe of the operationally necessary
nominal size and a variable concrete or steel casing.
Fig. 27 shows such a DN 400 / external diameter 860
mm vitrified-clay/reinforced concrete jacking pipe.
Fig. 27: Vitrified-clay /
reinforced concrete
jacking pipe
6.6 Quality Safeguarding in Sewer
Construction
Under A 125 only specialist companies having experienced
personnel and appropriate equipment may be entrusted
with pipe jacking. Capability is deemed proven
if the company holds an appropriate certificate from the
quality partnership ”Quality Safeguarding in Sewer Construction”.
The quality and testing stipulations include
for micro-tunnelling the two assessment groups V3 and
V2:
V3 covers trenchless construction of sewers and
drains in all materials ≤ DN 250.
V2 covers trenchless and unmanned construction of
sewers and drains in all materials and nominal sizes
using controllable pipe jacking systems with automatic
recording of jacking loads and continuous
recording of positional deviation.
In the General and Specific Requirements and with
respect to companies’ equipment special experience
and reliability of the companies and personnel deployed
and controllable pipe jacking plant are required,
amongst other things, in the quality and testing stipula-
tions for both groups. The requirements must also be
met by subcontractors.
In April 1998 Quality Safeguarding in Sewer Construction
listed for assessment group
V2 72 certified firms and
V3 49 certified firms.
Micro-tunnelling Page 23
Another 19 applications were to hand. Clients have thus
a wide choice of competent firms, facilitating the necessary
competition. In keeping with the requirements of A
125 and proficient performance, clients should incorporate
in the supplementary contract terms the following
text conforming to VOB:
Bidders must provide proof of the requisite specialist
skill, operative capability and reliability and also a
quality-assurance system comprising outside and self
monitoring. The requirements of RAL quality and the
GZ 961 testing rules must be fulfilled. Proof is
deemed given if the company holds the appropriate
RAL Quality Mark of the quality partnership ”Quality
Safeguarding in Sewer Construction”. Alternatively
an outside monitoring agreement for the individual
operation concerned may be submitted; the requirements
of the RAL quality and testing rules must be
met.
Because of the difficulty of thrust-boring operations their
requirements are quite exceptional, including relevant
knowledge possessed by only a limited number of sewer-construction
companies. A glance at the number of
certificates awarded in the last 10 years – since the quality
partnership ”Quality Safeguarding in Sewer Construction”
was formed – substantiates this. 1236 certifications
for the assessment groups A1 and A2 in public
sewer construction contrast with a total of 169 certificates
for unmanned and manned thrust boring. The
recommended form of competition for jacking-work
contracts is therefore a Limited Invitation to Tender following
a public eligibility competition.

Page 24 Micro-tunnelling
7. Cost-effectiveness
There is still a widely-held opinion that trenchless sewerconstruction
methods are very expensive and are more
economic than conventional sewer construction at great
depth or for specific cases, if at all. This misconception,
shared by many clients, is the reason why in some
regions there has not yet been any competition at all
between the two construction methods. Micro-tunnelling
may have long since proved itself in some key
areas as the more economic alternative and shows continuous
overall growth rates in Germany; but it still does
not get the attention it deserves by virtue of its technical
scope and environmental benefits.
Costs for sewer construction depend on local circumstances,
regulatory requirements and many constraints.
The price level at the time, companies’ available capacity
and the state of the economy play a part. It is therefore
impossible to make any generally valid statement about
costs for all regions. The most reliable way of finding the
most cost-effective solution is to specify projects in alternative
versions. If this is done over a period, a reliable
picture of the market situation is obtained and assessment
of when which construction project can be initiated
more cost-effectively made possible.
Nevertheless the large number of projects commissioned
and carried out in Berlin permits some statements
and a comparison with open construction to be
made. These statements are representative and the
trends implicit in them can be transferred. On the basis
of 1997 and 1998 tender prices costs have been compared
below between open construction and micro-tunnelling
in 4 examples. For the cost-effectiveness comparisons
to be placed in the context of the present study
the following constraints limiting the calculations have
had to be laid down:
– All figures relate to construction above the groundwater.
For projects in the groundwater costs would
shift even further in favour of micro-tunnelling.
– Installation of vitrified-clay pipes conforming to DIN
EN 295 in nominal sizes DN 200, 250, 300, 400, 500,
600 and 800 is considered, at depths of 1.75, 3.00,
4.00 and 5.00 metres. In the diagrams intermediate
depths have been interpolated and depth 6.00 metres
shown by extrapolation.
– The surface in the examples:
unpaved (Fig. 28)
interlocking paving bedded in gravel (Fig. 29)
concrete paving (Fig. 30)
bitumen paving (Fig. 31).
Other stipulations:
– minimum trench width as per DIN EN 1610
– soil excavated as average for classes 3, 4 and 5
– 50% soil replacement, i.e. import of backfil material to
ensure proper compaction
– spacing of manholes: 60 metres
– water-permeability test for all sewers and manholes
– width of the strip to be taken up on either side of the
trenches before final restoration of the roadway as per
Supplementary Technical Regulations for Line-Construction
Work (ZTVL)
– routing plan (open construction): in each section 6
junctions and connectors at each of the manholes
– routing plan (micro-tunnelling): reinforced concrete
starting and target shafts, spacing: 120 metres.
Starting shafts for jacking ≤ DN 300 with 2.00-metre
internal diameter, steel-plate cofferdam (liner plates) in
the upper section, for target shafts in ≤ DN 300 jacking
of steel-plate cofferdam (liner plates) with internal
diameter 2.00 metres. Starting shaft converted into
manhole as per Fig. 21. Starting and target shafts for
jacking ≥ DN 400 of reinforced concrete with internal
diameter 3.20 metres, steel-plate cofferdam in upper
section (liner plates). Inner manhole as per Fig. 23.
If the cost shares of open sewer construction are
analysed, soil excavation plus sheeting work, soil
replacement, refilling and compaction of soil and removal
of the trench sheeting, together with breaking-up
and restoration of the road surface are the significant
elements. With increasing depth the share for the trench
rises and to approximately the same extent the significance
of reconsolidating the road surface falls.
Delivering and laying the pipes and making the manholes
are of secondary importance.
In enclosed construction the actual jacking process
including jacking pipes always predominates – largely
irrespective of nominal size, depth and surface consolidation
– with a cost share of over 60 to 70%. Then come
the starting and target shafts at 25% of total costs at
most. Innovative solutions for constructing the components
in the starting and target shafts, and also increased
jacking distances and utilisation of the greatest
operationally justifiable lengths between manholes might
effect savings here. A relatively subordinate role is
played by the costs for integrated manholes and, as expected,
the costs for opening-up and restoring surfaces
are virtually insignificant.
The 4 diagrams show in terms of cost the relative
independence of jacking on the sewer’s depth. Each
intersection of the assigned curves denotes equality of

costs. It is apparent that jacking at shallow depth can be
more cost-effective, especially if valuable road topping is
encountered. The depth margins for cost-effectiveness
shown in the following sections would shift even further
and very clearly in favour of pipe jacking if for example
– dewatering were to be necessary,
– soil conditions were unfavourable and possibly complete
replacement with compactable filling soil were
necessary,
7.1
5000
4500
4000
3500
3000
2500
2000
1500
1000
DM/m
500
2,95 m - DN 200
3,80 m - DN 250
0
Berlin 1997
0 1,75 3,00 4,00 5,00 6,00
Open construction
Micro-tunnelling
4,40 m - DN 300
Micro-tunnelling Page 25
– prior re-laying of lines and/or measures to secure
structures, pipelines or other installations in the slope
area of open trenches were required,
– manual digging of pits were necessary,
– local conditions made elaborate trench sheeting indispensable,
– traffic diversions, traffic lights etc. were ordered as
supplementary measures in open construction.
Sewer-construction costs compared above the water table
open construction / micro-tunnelling using vitrified-clay pipes
Surface unpaved
5,20 m - DN 800
6,00 m - DN 600
Depth in meters
DN-200 DN-250 DN-300 DN-400 DN-500 DN-600 DN-800
Sewer-construction costs compared; surface unpaved
Where the surface is unpaved, jacking for
DN 200 at depths > approx. 2,95 metres
DN 250 > approx. 3,80 metres
DN 300 > approx. 4,40 metres
DN 600 > approx. 6,00 metres
DN 800 > approx. 5,20 metres
is more cost-effective than open laying. That the intersection
of cost-effectiveness is not reached for
nominal sizes DN 400 and DN 500 in the depth range
up to 6.0 metres considered is due to the high cost
shares for the starting and target shafts. For DN 400
the bore changes from 2.00 to 3.00 metres, so that at
depths of 5.00 metres the shares in total costs for
starting and target shafts are for example 29% /
26%.
Fig. 28

Page 26 Micro-tunnelling
7.2
6000
5000
4000
3000
2000
1000
DM/m
1,75 m - DN 200
2,55 m - DN 250
3,45 m - DN 300
0
Berlin 1997
0 1,75 3,00 4,00 5,00 6,00
Open construction
Micro-tunnelling
Sewer-construction costs compared above the water table
open construction / micro-tunnelling using vitrified-clay pipes
Surface interlocking paving
4,35 m - DN 800
4,95 m - DN 600
5,00 m - DN 500
5,45 m - DN 400
Depth in meters
DN-200 DN-250 DN-300 DN-400 DN-500 DN-600 DN-800
Sewer-construction costs compared:
surface interlocking paving bedded in
gravel
For surfaces paved with interlocking setts jacking
for
DN 200 at depths > approx. 1,75 metres
DN 250 > approx. 2,55 metres
DN 300 > approx. 3,45 metres
DN 400 > approx. 5,45 metres
DN 500 > approx. 5,00 metres
DN 600 > approx. 4,95 metres
DN 800 > approx. 4,35 metres
is more cost-effective than open laying.
Fig. 29

7.3
7000
6000
5000
4000
3000
2000
1000
DM/m
0
Berlin 1997
0 1,75 3,00 4,00 5,00 6,00
Open construction
Micro-tunnelling
Sewer-construction costs compared above the water table
open construction / micro-tunnelling using vitrified-clay pipes
Surface concrete paving
2,45 m - DN 300
3,40 m - DN 800
4,00 m - DN 500
DN 600
4,30 m - DN 400
Micro-tunnelling Page 27
Depth in meters
DN-200 DN-250 DN-300 DN-400 DN-500 DN-600 DN-800
Sewer-construction costs compared:
surface concrete paving
For concrete-paved surfaces jacking for DN 200
and DN 250 is more cost-effective at all depths
considered and for
DN 300 at depths > approx. 2,45 metres
DN 400 > approx. 4,30 metres
DN 500 and DN 600 > approx. 4,00 metres
DN 800 > approx. 3,40 metres.
Fig. 30

Page 28 Micro-tunnelling
7.4
7000
6000
5000
4000
3000
2000
1000
DM/m
2,25 m - DN 300
3,35 m - DN 800
0
Berlin 1997
0 1,75 3,00 4,00 5,00 6,00
Open construction
Micro-tunnelling
Sewer-construction costs compared above the water table
open construction / micro-tunnelling using vitrified-clay pipes
Surface bitumen paving
3,80 m - DN 600
DN 500
4,15 m - DN 400
Depth in meters
DN-200 DN-250 DN-300 DN-400 DN-500 DN-600 DN-800
Sewer-construction costs compared:
surface bitumen paving
For bitumen-paved road surfaces jacking for DN
200 and DN 250 is more cost-effective at all
depths considered and for
DN 300 at depths > approx. 2,25 metres
DN 400 > approx. 4,15 metres
DN 500 and DN 600 > approx. 3,80 metres
DN 800 > approx. 3,35 metres.
Fig. 31

7.5
1600
1400
1200
1000
DM/m
800
600
400
200
0
Berlin 1997
0 10,00 11,00 12,00 13,00 14,00 16,00 18,00
Open construction
Micro-tunnelling
Comparison of costs for constructing house connections above
the water table
(open construction / micro-tunnelling using vitrified-clay pipes)
Unpaved Interlocking setts Bitumen paving
Comparison of costs, house connections
There is nothing in the foregoing remarks about the
costs of house connections. These are covered in a
further example (Fig. 32) which likewise compares
the costs of open and trenchless construction. In
each case costs have been calculated for house
connections between 10.00 and 18.00 metres in
length where the surface is unpaved and for road
surfaces of interlocking paving bedded in gravel and
bitumen paving. The surface between roadway edge
and plot perimeter is – except in the case of the fully
paved surface – constant for all other examples at a
total width of 4.50 metres, comprising
– 1.00-metre-wide unpaved tree-protection strip,
– 1.00-metre-wide cycle track of interlocking paving
bedded in gravel,
– 2.00-metres-wide footpath of concrete paving
blocks bedded in gravel,
– 0.50-metre-wide mosaic paving bedded in sand.
The distance b from the collector under the roadway
varies between 5.50 and 13.50 metres, yielding
house-connection lengths between 10.00 and 18.00.
Micro-tunnelling Page 29
HC length in m
1/2 roadway 4,50
In both construction methods one trench over the
collector and one on the plot were allowed for. Pipe
jacking for connecting sewers where only one trench
is needed, e.g. in
the Berlin method,
jacking with underground connection to the
collector,
blind-hole boring
naturally result in even distinctly lower construction
costs and shift the cost-effectiveness threshold
clearly in favour of trenchless laying. But even with
two trenches and a completely unpaved surface the
cost-effectiveness of the jacking method is already
reached at a length of about 18 metres. With a roadway
of interlocking paving jacking is more economic
even at a house-connection length under about
10.50 metres and in the case of bitumen paving at a
length of less than 10.00 metres.
The remarks in the final paragraph of 7. apply analogously
to construction of house connections.
b b = 5,50 m
= 6,50 m
= 7,50 m
= 8,50 m
= 9,50 m
= 11,50 m
= 13,50 m
Fig. 32

Page 30 Micro-tunnelling
7.6 Social costs
Only construction costs actually incurred are considered
in the foregoing remarks. Compared with open sewerconstruction
methods the precisely calculable savings
brought by micro-tunnelling result primarily from
– the reduction in holes in the roads,
– the absence of soil excavation involving transport of
large bulks of soil,
– the reduction in prior pipe diversions,
– limitation of dewatering,
for the last two of which no figures are included in the
examples.
In everyday construction activities, however, further advantages
accrue for micro-tunnelling, such as
– limitation of traffic disruption,
– reduction in noise- and emission-levels,
– reduced accident hazard,
– elimination of damage to adjacent structures,
– sparing of trees and parkland and by
– elimination of time loss due to weather.
These are referred to as indirect or social costs; they
have particular significance for the environment and are
primarily a charge on the national economy. Impediments
to traffic flow, diversions, increased accident
rates, road damage on the diversion routes, disruption of
business, environmental nuisances such as noise, dirt
and smell are their main components. The expense
caused thereby in the case of open construction can be
considerable and in conjunction with additional soil exchange,
interim storage etc. can often reach the same
order of magnitude as the direct costs for a construction
project. While these social costs are not taken into account
in awarding contracts for sewer construction,
competition is distorted. That micro-tunnelling is nevertheless
more and more becoming an economic alternative
is evidence of its attractiveness.
8. Micro-tunnelling as an opportunity
for lower sewerage charges
Sewerage charges are determined essentially by the
finance and ongoing maintenance charges for the plant
and equipment for draining, moving and treating
sewage, with the associated installations. According to
Pecher, based on calculations by ATV, capital expenditure
on sewage systems amounts to some 75% and
thus has particular weight. (”Sewage disposal: costeffective,
far-sighted, affordable”, Cost-effective
Sewage Disposal Initiative (IWA), PO Box 101122, 45411
Mühlheim an der Ruhr).
Sewerage charges derive from operating costs, the
sewerage levy and imputed depreciation allowances and
interest charges. According to the above source the
cost shares yielded for public operators in all Federal
States are:
– sewerage levy 3.3 %
– personnel costs 16.4 %
– other operating costs 25.9 %
– interest 29.1 %
– depreciation 25.3 %
Outlay on interest and depreciation thus makes up almost
55% of the charge. It follows that charges can be
lowered by lengthening the service life of sewers.
The service life of sewage systems can be affected by
conscientious planning including careful selection of the
materials to be used, quality-controlled construction
work and proper operation. Reference is made in this
connection to the aforementioned article by Pecher and
to a publication by Kuck (”Paving the way for future
generations: a plea for technical and economic farsightedness
in the construction and operation of public
sewage systems”, offprint from Local-government economics,
Vol. 4, April 1997, obtainable from STEINZEUG
GmbH, Cologne).
Because of its particular technical requirements microtunnelling
provides the best basis for creating longlasting
sewers through high-quality construction.
The requirements made under ATV A 125 of jacking
pipes and their joint assemblies result in, amongst other
things, greater wall thickness, greater strength and lower
tolerances than in conventional pipes. The laying
process ensures greater precision and less effect on insitu
soil and the embedding. These specific features of
micro-tunnelling give increased security against stress
from shear loads, abrasion, corrosion, jetting etc. and
extend the sewers’ service life. A longer useful life permits
the depreciation period to be adjusted commensu-

ately, and the depreciation figures are lowered. This in
turn means lower sewerage charges. Further information
on this, with examples, may be found in the article
by Thymian, Möhring and Friede ”The economic significance
of quality assurance in sewer construction”
(STEINZEUG Information 1996).
Micro-tunnelling Page 31
9. Recommendations for carrying out
micro-tunnelling
In the public mind micro-tunnelling does not enjoy anything
like the importance due to it by virtue of its technical
and economic scope. Why is this? The main causes
are
– deficient awareness of the stage reached by developments.
For operators there is in many cases still
something exotic about enclosed sewer-construction
methods, which are decided on only when conventional
solutions appear inadvisable;
– uncertainties in planning, tender-specification and
preparatory matters;
– distrust, especially re: success in difficult subsoil conditions;
– hesitation by companies because the frequency of
use once capital has been invested cannot be
gauged.
In a modern technical development such as micro-tunnelling
there will be constantly new challenges for all
concerned. Any client and any planning consultant engineer
can however trigger impulses in order to increase
the cost-effectiveness of micro-tunnelling in his sphere
and have a hand in determining success in the market.
For this the following suggestions may be helpful:
1. In each sewer-construction project cost-effectiveness
comparisons should be drawn up for the open
and enclosed methods. In these, all factors affecting
the open methods in particular should be taken objectively
into account such as previous re-routing of
pipes, traffic lights and necessary digging up and
restoring of the road, soil replacement, dewatering
and the duration of construction work.
2. Where a cost-effectiveness comparison shows
approximate equality, the market should be challenged
with alternative specifications.
3. Micro-tunnelling is unsuitable for short underground
crossings of embankments, railtrack, waterways or
road intersections. The longer a construction site,
the more favourably do the relatively high cost
shares for investment in this technology pan out.
4. Frequent invitations to tender for micro-tunnelling
work are signals to contractors that investing in
modern technology might be worthwhile.
5. Standardisation of the major elements in pipe
jacking, starting, target, by-shafts and intermediate
shafts and – where necessary and feasible – their
subsequent incorporation in the sewage system as
inspection shafts are a contribution to rationalisation.

Page 32 Micro-tunnelling
6. For every operator it should be possible to dispense
with intermediate nominal sizes such as DN 350, DN
450, DN 700, DN 900 etc. This provides a perhaps
unique opportunity to bring about an economically
rational limitation right at the initial stage of a modern
construction project. Economies in the production
and stocking of cutting heads and jacking pipes
would result.
7. For drafting the specification standard rating books
for the rating range Standard Rating Book 085,
March 1997 edition, should be used. This will ensure
a correct tender specification.
8. In their outline or annual contracts for recurrent work
operators should also include jacking of individual
sections of smaller nominal size and of house connections.
Global estimates can be employed here as
a simplified form of accounting.
9. Future construction projects will increasingly concentrate
on the areas of old sewage systems. Building
density, heavy traffic, valuable road fixtures and
underground facilities deserving protection in the
road cross-section are the prevailing factors here.
Under these constraints micro-tunnelling can bring
its benefits to bear distinctively, especially since it is
foreseeable that to reduce traffic problems in towns
and conurbations the owners of public roads will order
the payment of special charges for their use related
to duration and the amount of road occupied.
10. Development in micro-tunnelling is proceeding.
There will be new scope for additional use. In the interests
of more cost-effective solutions serious tenders
using technical alternatives should therefore be
given a chance.
Irrespective of all future developments, complete systems
for underground installation of sewers and drains
are however already at our disposal in the pipe jacking
systems available today, which have proved competitive
alternatives to the conventional construction methods
under competitive conditions. Their use is worthwhile
for all concerned and for the environment.
Further reference:
Möhring: Environmentally acceptable sewer and drain
construction by micro-tunnelling
Water-supply and waste-water engineering
handbook
5th edition, Volume 1: Pipe-system technology,
publ. Vulkan Verlag, Essen (1995)