Granular materials are widely used in many fields of civil engineering. For most of granular materials

under external stress

it is very easy to cause grain breakage

which will have an obvious influence on the mechanical behaviour of materials. In order to well describe the mechanical behaviour of easily crushed granular materials

a new model taking into account grain breakage influence is developed within the framework of elastoplasticity and the critical state theory. The model aims at describing the behaviour of soils with grain crushing under shearing and compression. For this purpose

the relationship between position of critical state line(CSL) and the plastic work is investigated using experimental results on Cambria sand. The constitutive equations are then established relating to the function of critical state line

using which a double-yield surface model accounting for particle crushing is proposed. The model is then used to simulate drained triaxial tests with high stress levels. The comparison of experimental results and model predictions show that this model can well reproduce the behaviour of granular materials subjected to grain breakage.