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
suction hopper dredgers are mounted with draghead or dragarm pumps
which increases the dredging depth and trims down the occurrence of
cavitation as suggested by John B. Herbioh (1992). This machine is limited
to dredging relatively low-strength material. Moreover, they cannot be
deployed in very shallow waters and instead grab dredgers should be used.
However, its dredging capacity is higher than that of grab dredger and it
can be mobilized in relatively deep-water region.
Trailer suction hopper dredgers are renowned for their mobility, versatility
and capability to operate in unfavorable sea conditions.
3. What is the purpose of formation of bunds in reclamation? (R1)
Reclamation works normally proceed behind the seawall to protect against
typhoon attack. In case where soft marine mud is encountered during
reclamation, bunds may be formed on planned alignment of road and
drainage works and locations of early development to displace mud to
other less important areas should mudwaves indeed occur. Reclamation
may be carried out in strips or even crossed bunds forming a grid. Hence, if
mudwaves really occur, they could be isolated and dealt with individually.
4. In case mud waves occur during reclamation, what are the possible
solutions to rectify the situation? (R2)
(i) Option 1 – Complete Removal of All Disturbed Mud
To remove all disturbed mud once mud waves occur is the fastest way to
treat the problem. After that, filling material is used for replacing the
disturbed mud. However, this option is a rather expensive option because it
involves dredging of all disturbed mud and replacement of large amount of
fill.
(ii) Option 2 – Accelerated consolidation of Disturbed Mud
This option involves placement of surcharging loads on top of mud waves,
together with installation of band drains to accelerate the consolidation of
disturbed mud. This method suffers from the drawback that sufficient long
time is required for the consolidation process of mud.
(iii) Option 3 – Partial Removal of Disturbed Mud
This option is a combination of the first two options in which the top weak
layer of mud is removed while the lower mud is treated with surcharging
with band drain installation.
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