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
18. Vertical drains can be installed in square and triangular patterns.
Which pattern is better? (R8)
Vertical drains are commonly installed in square and triangular patterns.
The zone of influence of vertical drains (R) is a function of drain spacing
(S).
For drains in square pattern: R = 0.546S
For drains in triangular pattern: R = 0.525S
The advantages of square pattern are that it is more convenient to lay out
and manage on site. However, triangular pattern is the most popular one
because it provides a more uniform consolidation between drains than
square pattern.
Fig. Square pattern and triangular pattern of vertical drains
19. How does overflowing in trailing suction hopper dredger affect
the water regime? (R4)
Trailing suction hopper dredger contains a large hopper for storage and
transport of dredged materials. The dredging operation is implemented by
a hydraulic dredging system including draghead, suction pip, pumps for
taking up the material from seabed and putting them into the hopper.
When dredging materials, overflowing may occur to increase the solid
loads in the hopper and improve the efficiency of dredging operation. The
removal of excess water and soil/water mixture with low density enhances
the storage of soils mixture with higher density. Hence, this lowers the cost
of dredging by increasing the rate of production. If no overflow is allowed
during the dredging operation, trailing suction hopper dredger can normally
183