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
of steel-gate dams, it saves both construction cost and time.
(iii) Rubber dams can be designed with longer spans without piers while
steel-gate dams require intermediate piers for long spans.
13. How do we compare air-filled and water-filled rubber dams? (C6)
Most of the existing rubber dams are of air-filled types. Water-filled rubber
dams are not preferred for the following reasons:
(i) By giving the same sheet length and dam height, the tensile stress for
water-filled dams is higher than that of air-filled rubber dams.
(ii) A significant size of water pond is normally provided for water-filled
water dams for filling the rubber dams during the rising operation of
dams.
14. Under what conditions should engineers consider using stilling
basins? (C7)
Stilling basins are usually introduced to convert supercritical flow to
subcritcal flow before it reaches downstream. A typical stilling basin
consists of a short length of channels located at the source of supercritical
flow (e.g. end of spillway). Certain features are introduced to the basins like
baffles and sills to provide resistance to the flow. As such, a hydraulic jump
will form in the basin without having conducting significant amount of
excavation for the stilling basin if baffles are installed [31].
15. When a drainage system (i.e. u-channels with catchpits) is
connected to a main drainage channel, a segment of short pipe is
used. What is the reason of such arrangement?
There are three scenarios of such connection arrangement: (a) a new
drainage system is connected to an existing drainage channel (b) an
existing drainage system is connected to a new drainage channel (c) a new
drainage system is connected to a new drainage channel.
For all scenarios, what engineers consider is the total amount of differential
settlement or lateral movement to be encountered between the drainage
system and main drainage channel. For scenario (b) and (c), it is very likely
that substantial differential settlement will occur and this will cause damage
to the connecting concrete pipes. Therefore a segment of short pipes are
designed so that they serve to provide flexibility to the pipes in case of
uneven settlement occurring between drainage system and main drainage
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