As a unique geological material, the granular material-clay mixtures (GCM) constitute the special geological environment such as the ice water accumulation layer, the debris flow accumulation layer and the collapse accumulation layer etc, and it is widely distributed in the valley area of SW China. In this paper, the two-dimensional discontinue program called PFC^2D was used, to establish the GCM model soil samples with different skeleton contents and carry out a series of numerical biaxial tests. The change effect of skeleton content on the mechanical properties of GCM was investigated from the macro level (stress-strain characteristics, volume change behaviors, failure modes, shear strength parameters) and the micro level (distribution of the particles and of the contact force, contribution degree of various contact types to the contact force). In addition, the relationship between macro and micro phenomena was discussed emphatically. It is found that the load-bearing body of GCM uses 30 % skeleton content and 70 % skeleton content as the two critical points to transition from the filling particles to the skeleton particles in turn. The corresponding macro-mechanical changes of GCM also take these two levels of skeleton content as the critical points. When the level of skeleton content exceeds these values, the macro-mechanical properties of GCM will change significantly.

Granular mixtures; Skeleton content; Thresholds; Macro-micro mechanical properties; PFC distinct element program