By analyzing the micromechanics of the two-dimensional ideal particles (disc) under direct shear test

the movement during the shearing is investigated.  The formula described the maximum shear stress in the regular dense packing condition is established. In addition

following the direct shear simulations of the four samples with different particle size distributions

application of the formula which could predict the maximum shear stress was discussed. The results show that  the maximum shear stress is depending on two parameters namely boundary effect parameter and the non-boundary effect parameters

and these two parameters keep the same under the regular dense packing when the vertical loading is constant. For the general packing

the boundary effect parameters remained unchanged

and the non-boundary effect parameter is linearly decreases with the d

10

d

30

and d

60

.