A practical method for determining parameters of Gibson's soil model

Although the variation of shear modulus with depth can be considered in Gibson's soil model, it has always been a problem for engineering practice to determine the parameters in the model. Based on both oedometer test results of soils and a hyperbolic model using the secant modulus method by Wei Rulong (1980), a method for determining the parameters in Gibson soils is proposed for both the single-layered and the multi-layered cases. The method can be applied to soils whose stress-strain behaviors of compression obey the hyperbolic model using the secant modulus method. The results of analyzing several representative project sites in coastal regions of Zhejiang Province, China show that the special Gibson soils with a value of zero for shear modulus at ground surface keep nearly non-existent. Through the case study of a foundation treatment project using surcharge combined with the vacuum preloading technology, the multi-layered Gibson soil model with parameters calculated by means of the proposed method is thoroughly compared with other models with respect to the settlement prediction. The multi-layered Gibson soil model can give a settlement prediction with remarkably higher precision, and is also convenient in engineering applications. In the case that the effective reinforcement depth of ground is in the normal range, the Gibson soil model is recommended instead of the traditional models which ignore the variation of shear modulus of soils with depth.