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
(iii) For pipes with spigot and socket joints, it enables pipes to be
supported along pipe lengths instead of pipe sockets. Otherwise,
uneven stress may be induced and it may damage the pipes;
(iv) To provide a platform for achieving correct alignment and level during
and after construction.
6. What is the purpose of granular bedding for concrete pipes? (ED2)
In designing the bedding for concrete drainage pipes, granular materials
are normally specified instead of soils containing a wide range of different
particle sizes. The main reason of adopting granular material free of fine
particles is the ease of compaction as it requires very little tamping effort to
achieve a substantial amount of compaction and the crushed aggregates
readily move to suitable place around the pipes [67]. However, the use of
granular materials has the drawback that a stable support can hardly be
provided for the drainage pipes. In particular, it cannot maintain an
accurate slope and level for the bedding of concrete pipes. Most pipes are
gravity pipes and the accuracy in level is essential to maintain the flow
capacity.
Fig. Bedding of concrete pipes
7. Should engineers consider embankment condition and trench
condition when considering flexible pipes? (DD3)
The structural capacity of flexible pipes (e.g. plastics and metals) is derived
from ring bending stiffness. Owing to creep or relaxation the ring bending
stiffness decreases with time. Flexible pipes are liable to failure by
excessive vertical deflections, ring bending strain and buckling.
For rigid pipes, the shape of embedment determines the amount of loads
on pipes. For trench condition, the side walls of the trench provide frictional
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