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
For vertical elliptical pipes, it requires less excavation during trench
installation owing to its narrow span. Moreover, backfill loads on the pipe is
reduced when compared with circular pipes. Also, owing to its geometric
shape, it is mostly used where there is limitation of horizontal clearance.
From hydraulic point of view, vertical elliptical pipes allow higher
self-cleansing velocity under dry season.
4. Sometimes, “TOP’ are observed on the surface of concrete pipes.
What does it mean?
It is obvious that pipes should lifted up and laid with “TOP” up. Otherwise,
cracking may occur in the portion labeled “TOP” because they are not
supposed to take up significant loads on the sides of the pipe.
In fact, the reinforcing cage in concrete pipes can be circular or elliptical.
For pipes with elliptical reinforcing cage, it may contain the label “TOP” on
its top. Elliptical reinforcing cage is more effective to resist loads because
the reinforcement is mainly placed on the tension side of the concrete pipe.
As such, the use of elliptical reinforcement needs less steel than circular
ones for the same loading carrying capacity.
Fig. Oval reinforcement in concrete pipes
5. What are the functions of bedding under stormwater drains? (ED2)
Bedding, which are normally made of granular materials or concrete,
serves four main functions as suggested by O. C. Young and J. J. Trott:
(i) To enhance a uniform support under pipes in order to reduce the
bending moment longitudinally;
(ii) To increase the load-supporting strength of the pipes;
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