In recent years, considerable attention has been given to the formulation of constitutive equations for soil media. elastic models, endochronic models, and many elasto-plastic models with various degrees of complexity have been developed. prevost (1986) proposed a multisurface plasticity model to describe the soil nonlinearity, elasto-plasticity, hysteretic behaviour and stress path dependency including shear stress induced anisotropy. yielding is controlled by a set of nested yield surfaces which are described as a family of ellipsoidal cylindrical surfaces in the principal stress space. during shearing, the motion of the yield surfaces was expressed by a combination of the isotropic and kinematic hardening rules of plasticity. the model requires a set of parameters related to each yield surface. these are the geometric configuration of the yield surfaces and their associated plastic parameters. prevost used the model to analyze a number of soil-structure interaction problems. however, the verification of the capabilities of the model has been carried out by prevost alone. this is due to the complexity of the model, and the insufficient information in the literature regarding the techniques used for the identification of the model parameters, the details of the constitutive equations and the hardening rule. the objective of this research work is to asses merits and shortcomings of prevost's model. the mathematical derivation of the model parameters, the constitutive equations and the hardening rule are also presented in detail. the accuracy and the versatility of the model are highlited by comparing the model predictions with the actual tests data. a laboratory testing program provided some of the data to be used in this research work. the soil tested was a crushed quartz sand. the following tests were performed.