A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
services.
(ii) Small size of pipes.
7. Would pipe ramming increase the vertical soil loads on installed
pipes? (PR2)
Consider a certain cross section along the line of pipe ramming. When the
pipe is rammed close to the cross section, the horizontal and vertical soil
pressure would increase owing to the effect of soil compaction brought
about by dynamic ramming operation. Upon reaching the cross section,
soil pressure is redistributed around the pipe such that the vertical pressure
above the pipes is reduced while the vertical pressure in pipe abutment
locations is increased. When the pipe is advanced further, the load on
pipes tend to increase owing to reorientation of soils around pipe wall.
Finally, when the pipe is rammed some distance away from the cross
section, a stable state is achieved in which there is smaller earth pressure
on the pipe’s top and higher vertical soil pressure on soils at both sides of
the pipe.
8. What are the situations which warrant the use of pipe ramming
instead of other trenchless methods?
There are two main distinct advantages of pipe ramming:
(i) Settlement and heaving of existing ground.
Where a pipe have to be installed under an existing railway or
heavily-trafficked highway, it is almost impossible to install the pipes
by open excavation. In particular, if the pipes to be installed are of
shallow depth, the use of some trenchless methods (e.g. pipe jacking
and heading) may cause considerable ground settlement because the
soil loss within shallow zone would induce larger settlement. As such,
the use of pipe ramming could resolve this concern. Pipe ramming is
a displacement method which generally would not result in ground
loss. For open-ended steel casing, the soils inside the pipe are not
removed until the entire casing is installed in place.
(ii) Muck Disposal
For microtunneling, spoils are removed from the excavation face in a
slurry so that the spoil are wet. Hence, sufficient space has to be
provided to allow for drying of spoils or the wet spoils have to be
removed off site immediately. For pipe ramming slurry is not used so
that the spoil retains only it natural moisture content. Therefore, it is
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