-35.0°
-400'
Concrete Caissons
7.6
Description. Precast caissons of reinforced concrete are sunk in position on a levelled rubble mound. This mound is founded on sand fill which replaces existing soft seabed material after dredging. The outer crane rail is supported on the caissons and the inner on piles driven after reclamation.
SOFT CLAY
*14.25'
M.M.H.W. +7 1′′
M.L.L.W. +2.0'
0.90 C.D.
CONTAINER-CRANE TRACK 50' GAUGE
1 IN 100
R.C. CAISSON 4C'x50'x40'
GRANULAR
FILL
APPROX. EXISTING SEA BED -26.0°
40,0′
RUBBLE
MOUND
50.0
SAND
FILL
COMPACT SOIL
RECLAMATION
·20′′x 20′ PRESTRESSED
CONCRETE PILES
FILTER
STONE
-42.0
FILL
SOFT
CLAY
7.6
7.7
7.8
7.9
Advantages:-
(a) It provides a robust and stable structure.
(b) Various container-crane gauges can be used without altering the caisson design. (c) This type of construction has proved successful elsewhere.
Disadvantages:-
(a) The caissons are difficult to manoeuvre and place accurately due to their large size. (b) A special site requiring extensive temporary work is necessary for manufacture of
the caissons.
(c) 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.
(d) There is a possibility of settlement which would result in difficulty with the container
cranes.
(e) It is a comparatively expensive form of construction.
Order of Cost. From $11,500 to $14,500 per ft. run of berth depending partly on depth of dredging required.
7.10 Suitability. Suitable where there is not much removal of soft material from the seabed
required to reach a firm strata.
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