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
Level One (Core FAQs)
Part II: Reclamation
1. What are different approaches for reclamation in deep water region
and shallow water region? (R3)
To illustrate the different approaches adopted for reclamation in deep water
and shallow water region, the following example is used:
In deepwater region, consider the seabed level is –8.5mPD. After laying of
geotextiles and 1.5m thick sand blanket, the top level of sand blanket is
about –7mPD. Split barges are deployed for dumping public fill to –2.5mPD.
Afterwards, end dipping of public fill by trucks will be carried out up to
+2.5mPD which is the designed reclamation level. Between level –2.5mPD
and +2.5mPD, it is too shallow for split barges to enter the water, thus the
method of end dipping is used instead.
For shallow water region, the seabed level is taken as –5.5mPD in this
example. With the laying of geotextiles and 1.5m sand blanket into position,
the top level of sand blanket is about –4mPD. In this case, split barges are
also used for reclamation work between the level –4mPD and –2.5mPD.
After that, if end dipping is used for reclamation work above –2.5mPD, then
in considering the relative thin layer of fill above seabed (1.5m sand
blanket + 1.5m sand blanket), it stands a high chance that mud wave would
occur in seabed. Therefore, half-loaded derrick barges are employed for
reclamation up to level 0mPD. With a thicker layer of public fill now, end
dipping can then be used for reclamation between 0mPD and +2.5mPD.
This above reclamation sequence is just an example to demonstrate the
different considerations for reclamation in deep water and shallow water
region.
2. In dredged reclamation, what are the considerations in selecting
between trailer suction hopper dredgers and grab dredgers? (R4)
Trailer suction hopper dredgers are vessels which remove material off the
seabed through hydraulic suction by using pumps. During the dredging
operation, a mixture of soil and water is transported through suction pipe to
storage hoppers. Significant turbulence inside the hoppers keeps the
dredged mixture in suspension and this should be minimized to enhance
the material to settle swiftly prior to the process of overflowing. Trailer
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