Outwash deposit is one of the typical mixed materials

which is made up of soft soil grains and hard rock mass; and it is very difficult to determine its mechanical parameters and analyze its mechanical characteristics. Digital image reconstruction method is used here to help construct the structure of outwash deposits and to reflect the distribution of stones as well as the feature of clump. So a modeling method with particle discrete element method based on image recognition is built up

by which the laws on mechanical parameters of media distribution

strength of soil particles are researched. Then deformation characteristic

peak strength and shear strength after peak are analyzed. It is shown that the deformation curve before peak strength presents a feature of nonlinear hardening process

while it is like perfect plasticity after peak strength; composite friction angle of mixed material will decrease with the increase of bonding strength; when the stone content is less than 25%

composite shear strength approximately is equal to soil strength; when the stone content is higher than 25%

the shear strength will increase with the increase of stone content. Due to the effect of rock structure

the correlation coefficient between stone content and friction angle is greater than that between stone content and cohesion strength; and it can be concluded that the actual friction angle of geology deposits of Gushui Hydropower station is 0-8 degrees higher which is agreement to engineering conclusion. This method can consider stones of large size

which is a great difficulty in laboratory test

and can be a beneficial method for mechanical test in determining shear strength.