TNAG-0273-FCO40-309-Scheme-for-development-of-container-terminal-at-Hong-Kong-1970 — Page 52

CONSOLIDATION – %

20

40

60

80

100

FIG. 3: CONSOLIDATION OF CLAY / TIME

TIME - YEARS

1 2

5 10 20 50 100

NO SURCHARGE

·I OʻSURCHARGE

-20′ SURCHARGE

10.26 With up to 20 ft. of additional fill as surcharge above 40 ft. of fill, the required spacing of 12-in. sand drains, to achieve 60% and 80% total consolidation of a 25-ft. layer of the very soft clay after 2 and 5 years is shown on Fig. 4.

10.27 From Fig. 3 it will be seen that although 20 ft. of additional fill as surcharge would reduce the time required for a given degree of consolidation by up to 40%, the increase in con- solidation achieved after only a few years is small. After 5 years, for instance, 30% would be achieved instead of 26% with no surcharge.

10.28 From Fig. 4 it will be seen that the required drain spacing to achieve a given degree of consolidation within 5 years would be reduced very little by surcharging with up to 20 ft. of additional fill, which seems to be the practical limit.

10.29 It is concluded, therefore, that surcharging is not worthwhile unless there is a plentiful supply of free filling material which is not required for other reclamation. Even then, results would not be very significant unless the site being surcharged is not required for some years.

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