A hypothesis that the skeleton deformation of clay is only the deformation of the interfaces of grains

and the deformation characteristics including nonlinearity and plastic deformation are controlled by the sliding of interfaces of grains within skeleton

is presented. Such a sliding can occur whenever the shear stress on interfaces of grains reach a critical value

and the direction range of sliding increases with the shear stress. This paper view that the sliding of interfaces of grains is a sort of damage in the clay skeleton

and there are two sorts of interfaces within the clay skeleton

the one contacts perfectly

and the other one contacts imperfectly. On plane

according to the relative distance from the stress circle to the initial sliding envelope line

the direction-range value of the sliding interfaces can be determined. The damage ratio is defined as the ratio of the previous direction-range values to its maximum value (determined by failure stress circle). The overall shear modulus is the weighting average of the perfect contact shear modulus and sliding contact shear modulus. The proposed model simulates the shear deformation for saturated clay under consolidated undrained condition reasonably well. In addition

the mechanical properties of the model can be conveniently obtained through conventional triaxial compression test; and the model is capable for predicting deformation behavior under various conditions

including varying hydrostatic stress and stress paths.