PORT WORKS DESIGN MANUAL PART 3 Guide To - The University ...

46the development schedule has not been determined during the design stage, the designershould liaise with relevant government departments or land developers and determine asuitable time interval after completion of reclamation for calculating the target residualsettlement. In any case, the designer should check with those bodies to see if there are anyspecial settlement requirements.For a typical reclamation in Hong Kong where the seabed is underlain by marine and alluvialclay, the following information may assist the designer to assess the residual settlement:• If the reclamation is near the shore where the thickness of the clay layer isabout 5 to 8 m, it is usually practical to limit the residual settlement arisingfrom primary consolidation to 50 mm for the drained method with preloadingand a reasonably tight construction programme.» If the reclamation extends to deep waters, with clay layer of about 20 m ormore, residual settlement of 250 mm can generally be achieved. The amountcan be further reduced by over-consolidation with additional surcharge, but thecost will be higher and the construction period will be longer. Overconsolidationwill also reduce the secondary consolidation, particularly for softmud.• The residual settlement due to creep of granular fill, with thickness of 10 to15 m in a typical reclamation, may be in the order of a few hundred millimetres.Treatment of the fill by the methods mentioned previously may be necessary toachieve the target residual settlement.The thickness and properties of the soil, the period of fill placement and fill treatment varyacross a reclamation site.Therefore, it is necessary to estimate the residual settlement indifferent portions of the reclamation to account for such variability.Where the presence ofmud lenses is suspected in the underlying strata, additional ground investigation should becarried out to identify their locations and to determine relevant soil parameters for settlementanalysis.Where the designer considers that resiltation of clayey or silty particles of the dredged soil isa problem at a particular site, its effect on settlement should be assessed.The amount of residual settlement estimated in the design stage should be verified by fieldmonitoring data (see Chapter 5 of this part of the Manual).