The shearing induced dilatancy is an important deformation characteristic of granular materials during loading process. As the minimal unit to remain stable under external load

void cell is used to characterize the internal structure of granular materials. Based on the shear process of the individual void cell

it is found that the volume change of void cell is dependent on the stress ratio and the shape of void cell. It is explained the microscopic mechanism of the phenomenon that the dense granular materials compress first and then dilate. The evolutions of the shape of the individual void cell and volume deformation in them during biaxial shear test are simulated by using discrete element method (DEM). The results show that

the void cell is enlarged along the direction of the maximum principal stress and the volume deformation in the void cell compression first and then dilate as biaxial compression proceeds. Moreover

localization phenomenon is observed in the volume deformation in local void cells from the numerical results

i.e. voids with large dilatancy exhibit in the form of oblique bands at large deformation stage. The mechanical analysis of individual void cells and DEM results of dense granular array show that dilatancy of granular materials is dependent on the microscopic geometry fabric and the transmission of the force in them.