TYPES OF QUAY STRUCTURE CONSIDERED
Concrete-Block Seawall
7.1
Description. The seawall is constructed by removing the soft seabed material, replacing by sand, dumping a rubble mound and setting concrete blocks on it. The front crane rail is carried by the seawall and the rear by piles driven after reclamation.
SOFT
CLAY
+14,25'
M.M.HAW. +7.1
M.L.L.W +2.0
0.00 ̊C.D.
CONTAINER-CRANE TRACK 50ʻ GAUGE.
IN 100
FILTER
APPROX. EXISTING SEA BED −29.0
STONE
RUBBLE
MOUND
-52.0°
RECLAMATION
~20"x 20′′ PRESTRESSED
CONCRETE PILES
FILL
SAND
FILL
SOFT CLAY
COMPACT SOIL
7.1
7.2
7.3
7.4
7.5
Advantages:-
(a) This type of wall is well known to Hong Kong contractors and is easily constructed. (b) Various gauges of container crane can be used without altering the seawall design. (c) The cost is comparatively low.
Disadvantages:-
(a) The amount of soft material to be removed is great in some places on the proposed quaywall alignment. Very deep dredging would therefore be necessary and a large volume of suitable sand fill, of which there is a scarcity, would be required. (b) There is a probability of settlement which would result in difficulty with the container
cranes.
(c) Considerable diving work in comparatively deep water would be required during construction and this together with the large number of blocks to be placed under water would mean that this form of construction is likely to be comparatively slow.
Order of Cost. From $8,000 to $10,000 per ft. run of berth depending partly on the depth of dredging required.
Suitability. Suitable where there is not much removal of soft material from the seabed required to reach a firm strata.
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