Abstract: Surcharge preloading is an effective method of foundation treatment; and its effect can be reflected from the ground settlement caused by load of building after treatment. The value of the settlement is related to surcharge ratio and consolidation degree when surcharge is unloaded. There is still lack of simple and effective computational model about average degree of consolidation which ground should achieve before surcharge is unloaded (i.e. the problem of unloading control).A two-components consolidation model, in which nonlinear elastoplastic stress-strain relation of soil skeleton is considered, is put forward based on the principle of surcharge preloading and test curve. The consolidation differential equation of the model is derived. The result of calculation based on the model is more reasonable compared with traditional theories of unloading control. And the effects of permeability coefficient and ratio between elastic and plastic strains of soil skeleton on unloading control are discussed.

Key words: surcharge precompression, nonlinear elastoplastic consolidation model, unloading control