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
carry about 10% of normal load and this essentially increases the cost of
dredging operation.
If overflowing is allowed in the dredging operation, it shall work on
unrestricted basis as the rate of overflow is nearly constant over the entire
overflowing process. For dredging with overflowing, the particle size
distribution of sand may differ from the in-situ grading because overflowing
tends to remove the fine content of sand.
The loss of sediment associated with overflowing poses environmental
problems to the nearby water zone in eth following ways:
(i) increased sedimentation
(ii) decrease in dissolved oxygen
(iii) increased turbidity
(iv) increased amount of nutrients
20. Why can vacuum preloading be employed to accelerate the rate of
consolidation?
In vacuum preloading, the drainage boundary of clay is isolated from the
atmosphere by a membrane. A partial vacuum (e.g. suction of 80kPa) is
applied within the membrane to reduce the water pressure so as to speed
up consolidation.
The rate of consolidation can be increased by surcharge preloading in
which the excess pore water pressure in clay is temporarily increased.
Alternatively, the rate of consolidation can also be increased by vacuum
preloading by a decrease in water pressure.
Vacuum preloading is generally faster in operation than surcharge
preloading which requires timely delivery of fill on top of clay. Moreover, it is
unnecessary to consider the stability criterion which surcharge preloading
should require.
21. Geotechnical Instrumentation is frequently employed for
monitoring the condition of reclamation. Sometimes two piezometers
are installed inside the same borehole. What is the reason behind
this?
For standpipes, they normally contain one plastic tube between its intention
is to measure water level only. However, for piezometers, they are used for
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