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
forces. Rounded stones have a high tendency to roll and inadequately
protect the channel bed and bank. The ratio of length to thickness of
angular stones should be less than 2.
If rounded stones have to be used, they should not be placed not steep
embankments. Moreover, the size of rounded stones shall be increased
(say 25%) with the corresponding increase in thickness of riprap layer.
9. Why is stoplog seldom used in drainage channels? (C4)
Stoplog consists of several sets of horizontal beams/logs stacked vertically.
For narrow openings, the logs span between support slots at the ends of
the openings. For wide openings, intermediate removable support posts
may be required. They are prevalent in the past because of its low
establishment cost, simple erection and easy operation.
However, there are also several drawbacks of this closure system. Since it
requires a long lead time to mobilize workers and equipment for installation,
it needs an accurate long-range weather forecast to allow for the long lead
time. The situation is even worse for wide stoplogs which requires special
lifting equipment for installation of intermediate support posts. When
compared with time required to close sluice gates, the installation time of
stoplogs is much longer. Moreover, a storage building has to be provided to
prevent material loss by theft and damage by vandalism.
Fig. Stoplog system
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