Rock and soil aggregate（RSA）is a complex mixture of soil and rock

and its macroscopic deformation and mechanical characteristics are closely related to the spatial distribution of rocks.To study the deformation and failure mechanism of RSA with different directional distributions of rock blocks

a two-dimensional numerical RSA model was constructed using the FISH language in the particle flow code（PFC）.Different directions of oval shaped rock blocks were generated and

then

numerical simulation of biaxial compression tests were conducted with single rock block and multi rock blocks

followed by a discussion of the deformation and failure mechanism.Results indicated that the location of crack initiation in the soil was different when the angle of rock blocks were different.With the increase of the degree between rock blocks’ short axis and the direction of minimum principal pressure axis

the cohesion of the RSA decreased firstly and then increased

and the angle of internal friction decreased gradually.The crack in soil increased rapidly at the stage of gentle stress growth before reaching the peak strength

while the increase rate decreased gradually when the residual strength was reached.The pattern of shear failure zone was often different if the degree between rock blocks’ long axis and the maximum principal pressure axis are different.