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
culvert and block the flow subsequently;
(ii) To prevent access into the culvert by children.
However, screens are not always placed at culvert inlet and they should be
determined case by case. For trash or security screens installed in place, it
would inevitably trap floating debris and rubbish. Unless they are regularly
removed, it would eventually lead to rise in upstream water level leading to
local flooding.
For new culvert, there is a trend that the use of trash screens is declining.
Trash screens are only placed in culvert inlet where there is a high risk of
blockage history. Instead the need of trash screen can be eliminated by
adopting the following design features:
(i) There are fewer changes of cross section, fewer bends and smooth
transitions into the culvert. As such, it would provide fewer locations
to trap debris and trash.
(ii) Provision of good access to the culvert to facilitate regular
inspection.
(iii) The culvert should be not designed too long to enhance easy
access to clear a blockage.
8. What are the differences in applications between pipe culverts and
box culverts?
Basically, a culvert means a covered hydraulic structure which conveys
fluid. Therefore in a broad sense, pipe culverts in a small scale represent
normal pipes like precast concrete pipes.
In terms of hydraulic performance, circular section is the best geometrical
sections among all. Therefore, for relative small discharge, precast
concrete pipes and ductile iron pipes are normally used which are circular
in shape. But for applications of very large flow, precast concrete pipes and
ductile iron pipes may not be available in current market. In this connection,
cast-in-situ construction has to be employed. It is beyond doubt that the
fabrication of formwork for circular shape is difficult when compared with
normal box culvert structures. However, circular shape is the most
hydraulic efficient structure which means for a given discharge, the area of
flow is minimum. Therefore, it helps to save the cost of extra linings
required for the choice of box culverts.
However, box culverts do possess some advantages. For example, they
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