Abstract：Based on the experiment of critical slope made up of dry sand-gravel mixtures，it is confirmed that self-organized criticality(SOC) in granular mixtures is strongly influenced by non-homogeneity of granular material. Using large-scale coarse grained soil test system，the relative density and direct shear characteristics of sand-gravel mixtures in different size distribution are tested. The occurring condition of SOC and its mechanism are discussed. It is observed that，along with the increment of non-homogeneity，the piled structure becomes more complex，and the sliding resistance among sands grows accordingly. Furthermore，it is concluded from experiments that if the physical characters determined by structure of non-homogenous granular mixtures，the multiform failure states and higher energy dissipation can cause sufficient restraint on disturbing-feedback propagation，granular mixtures will maintain overall stabilization. As a result，a large-scale system can present the SOC as well.
