Vertical deformation of a reclamation surface

One of the most important requirements for a reclamation project is the final design level. This level is to be guaranteed at time of hand-over time or after a certain specified design life of the structure. An accurate prediction of the settlement behaviour is therefore essential. This becomes more and more challenging when the subsoil consists of a soft compressible layer. 

When specifications are given in terms of settlement, in general 2 types of requirements apply  

It is the responsibihty of the designer to accurately predict the settlement in time as a function of the loading conditions and to account for this behaviour in the planning of the construction works. 

At the time of handover, the (sub)soil does not necessarily have to be completely consohdated. If the allowed residual settlement is larger than the expected secondary compression, then part of the residual settlement may comprise some primary settlement as well. In that case there is no need to wait for full consolidation of the subsoil during the construction period. It is, in that respect, noted that a much longer time is required to obtain an increase of the consolidation percentage from 95% to 99% than for instance from 80% to 95%. 

On the other hand, the secondary compression may possibly exceed the allowable residual settlement. In that case a preload by means of a temporary surcharge will be needed to reduce the secondary compression to an allowable limit. 

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