A Self-Learning Manual - Institution of Engineers Mauritius

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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 338
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU easier to handle in-situ soils than wet spoils. On the other hand, the amount of spoil produced by pipe ramming is smaller when compared with pipe jacking and microtunneling. 339
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A Self-Learning Manual - Institution of Engineers Mauritius

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