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The majority of the pipeline is situated in public
areas. The Walchenseestrasse (in Berlin
Köpenick, the Grünau district) is a residential
street carrying little traffic, with only a thin
layer of surfacing. Nor are there any trees or
other obstructions to pipe-laying. In this section
the height of cover is only 1.40 m to 1.50 m.
These would have been ideal conditions for
replacing the pipeline in conventional open
trenches, except that it would have needed to
cross below a privately owned piece of land. In
the interests of the owner of the land, Berliner
Wasserbetriebe decided to make a trenchless
crossing below the land affected, with no change
of route, and therefore minimise any claims the
owner might be entitled to make.
The task was therefore to replace a DN 300
pressure sewage pipeline of grey cast iron with
a new ductile iron pipeline of DN 500 nominal
size, trenchlessly and along the same route, and
in so doing remove all the material of the old
pipe from the ground without in any way affecting
the piece of privately owned land. The complete
removal of the material of the old pipe is
an essential requirement whenever pipes are
replaced in Berlin. At Berliner Wasserbetriebe
the decision was made to leave the method of
replacing the pipeline to the contractor. Its proposal
to replace the pipeline by the press-pull
technique with additional soil removal landed
the contract for the Berlin branch of the Josef
Pfaffinger Bauunternehmung GmbH company.
The press-pull technique has a long tradition
in Berlin. Every year around 10,000 m of
water pipelines of nominal sizes from DN 80 to
DN 400 are replaced by this technique. Berliner
Wasserbetriebe has created a set of rules of
its own for this, in the form of company standard
WN 322. These rules are closely related to
DVGW-Arbeits blatt GW 322-1 [1], but allow
higher tractive forces for ductile iron pipes with
positive locking joints.
The problems with this installation project were,
above all, the very large amount of upsizing
called for by the change of dimension through
two nominal size increments, and the relatively
small height of cover.
52
Ø = 300 mm
r = 150 mm
Old pipe
DN 300
grey cast iron
Amount
of upsizing
max Ø = 700 mm
New pipe
DN 500 ductile iron
Fig. 3:
Determining the amount of upsizing
r = 350 mm
Under DVGW-Merkblatt GW 323 [2], the
amount of upsizing is the difference between
the inside radius of the old pipe and the radius
of the enlarged passage required (Fig. 3). In this
case the diameter of the enlarged passage was
about 700 mm so the radius was 350 mm. This
value was obtained from the outside diameter
of 636 mm of the socket of the DN 500 BLS®/
VRS®-T push-in joint plus the 5 mm thickness
of the cement mortar coating (ZM-U) plus the
oversize required. The amount of upsizing was
therefore 200 mm. This amount of upsizing was
the criterion for the cover required for the pipes
and for the minimum distances from neighbouring
pipelines. The cover for the pipes may
not be less than 10 times the amount of upsizing
if damage is to be avoided to surfaced ground.
For the present operation, this figure would
have been at least 200 cm. However, because the
cover available was only 1.40 m to 1.50 m, the
normal press-pull technique was not an option.
The solution therefore lay not in displacing the
excess soil but in removing it – a totally new
procedure when combined with the familiar
press-pull technique.
Consequently, the Josef Pfaffinger Bauunternehmung
GmbH company had to collaborate
with the TRACTO-TECHNIK GmbH & Co.
KG company to develop new machinery to cater
for this ambitious project. The pipe supplier
assisted with this.
150 200
350
FGR® / EADIPS® 46