It is well known that the Cam-clay model overpredicts the observed values of strain-increments for changes of stress ratio (η)at small values of η，even though excellent agreement is found for changes of η at large values of η.Howeve,strains predicted by the modified.Cam-clay model are shown to be in excellent agreement with observation. This paper first presents a model(termed a non-coaxial modiied Cam-clay model)which incorporates a non-coaxial term in the modified Cam-clay model.Secondly,we carried out bifurcation analysis using the model presented in this paper during undrained shear under plane strain condition.
Results of bifurcation analysis using the non-coxial modified Cam-clay model were then compared with the results of bifurcation analysis using the non-coaxial Cam-clay model.Bifurcation stress ratio using the non-coaxial modified Cam-clay model is larger than that using the non-coaxial Cam-clay model.Predicted slip surfaces from the distributions of maximum shear strain,effective mean normal stress,generalized stress deviator,pore water pressure and stress ratio are almost the same and resemble slip surfaces that are actually observed This is not based on the difference between non-coaxial modiied Cam-clay and non-coaxial Cam-clay model.