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

A consideration of the economics of trenchless techniques
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).
Requirement 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.
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