should be accepted into this reclamation. Sufficient mud should be removed to leave not more than 10-ft. thickness of very soft clay over most of that area; this would involve dredging a 15-ft. thickness of mud.
10.32 Reclamation behind the existing breakwater could be treated with sand or paper drains
and whether these are to be installed would depend on:-
(a) how soon it is decided to bring the reclamation into use,
(b) observed settlements after reclamation, and
(c) the feeling of the Terminal operators on how seriously their operations would be
affected by the anticipated settlement in this area.
For estimating purposes in this Report it will be assumed that the drains would be in- stalled on the whole area of the reclamation behind the existing breakwater. The drains would be 12-in. sand drains at 7-ft. centres or paper drains at 4.5-ft. centres, whichever is found to be the more economical after calling for tenders.
10.33 As noted in paras. 10.14 et seq. & 10.18 et seq. some settlement should be expected for a few years after the reclamation is filled, even if mud replacement or sand drains are adopted. If it is necessary to use the reclamation for container operations at the earliest possible date, the initial fill should be brought higher than the planned final level to allow for this, but as consistent with surface-water drainage and container operations.
10.34 As recommended and adopted by the consulting engineers for the Kwai Chung Reclama- tion and for the same reasons, tipping of fill from lorries to form the reclamation should be preceded by the bottom-dumping from barges of a layer of sand or other granular material to blanket the soft clay forming the seabed. If this is not done, the mud would be displaced into a semi-fluid wave in front of the fill which would hamper further re- clamation and the resulting mixture of mud and fill material would lead to differential settlement in the reclamation. The blanket of granular material would also hasten the consolidation of the soft clay by ensuring free drainage of its upper surface.
10.35 Sand is in short supply and rather expensive, whereas experience with bottom-dumping decomposed granite has shown that some of the fines are washed away and those which remain tend to settle in thin layers which consolidate very quickly. It is recommended therefore that the layer of granular material to be dumped initially should be selected coarse decomposed granite.
Quantities
10.36 The quantities of filling material required for the Container Terminal cannot be viewed in isolation from the reclamation of the remainder of Gin Drinker's Bay. The estimated relevant quantities are shown in Table 5. The figures for soft can be increased if the whole of the rock capacity is not used. The rock quantities are the maximum acceptable to conform with the recommendations of this report.
TABLE 5: RECLAMATION QUANTITIES
Location
Area, acres
Soft
Capacity million cu, yds.
Rock
Total
Reclamation already approved excluding
Container Terminal area...
46.0
2,2
0.6
2.7
Reclamation already approved & now
proposed for Container Terminal
39.9
2.6
2.6
Additional reclamation for Container
Terminal
49.9
0.6
* |
3.1
3.7
Additional reclamation for Desalination
Plant
5.7
0.4
0.4
Total reclamation
141.5
5.7
3.7
9.5
Reclamation for Container Terminal
Stage 1 (1st Phase)
10.9
0.7
0.7
Stage 1 (2nd Phase)
21.9
0.8
0.9
1.7
Stage 1 (Total)
32.8
0.8
1.6
2.4
Stage 2
26.3
1.0
0.6
1,6
Stage 3
30.7
1.4
0.9
2.3
Total for Container Terminal
89.8
3.2
3.1
6.3
45
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