The shear deformation of soil can not be considered sufficiently by Cam-clay model and the actual deformation characteristic of soil material can not be reflected in engineering projects. In the paper this disadvantage of Cam-clay model is theoretically analyzed firstly; and the idea of adopting different proportional coefficients to strain components induced respectively by shear stress and volume stress is proposed; then based on the idea and using the shear test results performed by Nanjing Hydraulic Research Institute

the Cam-clay model is modified; and the concrete stress-strain formulas of modified Cam-clay model are presented also. The comparison of the computed results of correlation between shear stress and axial strain by the improved model and the Cam-clay model shows that the shear deformation can be considered effectively in improved Cam-clay model. Besides

the four material parameters in modified model are easy to be measured.