MODELLlNG THE EFFECTS OF SURCHARGE ' TO REDUCE LONG TERM SETTLEMENT OF RECLAMATIONS OVER SOFT CLAYS: A NUMERICAL CASE STUDY

DAVID NASH

ABSTRACT : Long-term settlement of reclamations constructed over soft soils may be reduced by the use of temporary pre-loading, although there is often uncertainty over how much surcharge to use, and how long it should be maintained. An elastic visco-plastic constitutive model is described and its application in assessing surcharging strategy for reclamation schemes is discussed. The model is incorporated in a one-dimensional finite difference consolidation analysis with vertical and radial drainage of a multi-layer soil profile. The analysis allows the inclusion of vertical drain resistance a zone of peripheral smear around the drain, permeabilities that vary with void ratio, and creep both during and after primary consolidation. Drawing on data from the Bothkennar soft clay research site, the model is used to predict settlements beneath a hypothetical test fill, including the creep settlement behaviour when a surcharge is removed after different time periods. The behaviour during primary consolidation is back-analysed using Asaoka's and the hyperbolic observational methods, and both are found to under-predict the magnitude of the settlement.

 Key words: consolidation, creep, finite difference analysis, preloading, reclamation, soft clay, surcharge, vertical drains (IGC: D5/E13)