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

Table .1 provides an overview of the possible ways of protecting the joint with the
different variant procedures:
Table .1: Possible ways of protecting the joint
General requirements
Variant Outside protection Joint protection
Pulling-in of single pipes ZMU
Cement mortar protecting
sleeve plus sheet-metal cone
Pulling-in of pipe strings or
part-strings
ZMU
Cement mortar protecting
sleeve or shrink-on sleeve plus
sheet-metal cone 1)
1) Information on this subject can be found in our product catalogues. Shrink-on sleeves of
tape material should be avoided on directionally drilled pipelines if at all possible.
The two installation procedures mentioned above, namely the pulling-in of single pipes
and the pulling-in of pre-assembled pipe strings or part-strings, are used as dictated by
the amount of space available on site. In built-up inner city areas, it is, for the most part,
the pulling-in of single pipes which has to be considered. A launch pit about seven to
eight metres in length is required for this. Assembly and the protecting of the sockets
take place in the pit. Interference with the surface of the street can be even smaller if
the pipes are joined together on a mobile ramp. Depending on the governing conditions,
such as nominal diameter, supporting ground and the preparation of the sliding
surface of the pipe string, lengths of some hundreds of metres can be pulled in.
Example:
DN 200 ductile cast iron pipes with cement mortar coating, BLS ® joints and highpressure
locks, wall thickness class K9
• permitted tractive force F zul : 3 0 kN (PFA bar)
• weight of pipe G pipe : 271,5 kg = 45,25 kg/m ≈ 0,46 kN/m
• coefficient of friction µ = 1,0
What is thus obtained for the permitted length of the pipe string, from the formula
L perm = F perm / (G pipe * µ) = 350 kN / (0,46 kN/m * 1,0) ≥ 7 0 m
In many cases, the coefficient of friction µ that will occur will be appreciably less than
1.0, thus enabling substantially longer lengths to be installed. In this way, coefficients of
friction of between 0. and 1.0 were found in a series of measurements of tractive
force made on DN 00 pipes and the average was µ = 0.78 [ .11]
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