Abstract:

The soil-rock mixture is a heterogeneous material consisting of high-strength rocks and a low-strength soil matrix, with complex interactions among its mesoscopic components under loading. Considering the mesoscopic structural characteristics, the interface between soil and rock, as well as the interior of the soil matrix, are identified as the material’s weak points. Using the cohesive model, the initiation, expansion, and fracture of cracks at weak points are described, and a cohesive element insertion program is developed. Subsequently, using the results of direct shear tests, the material parameters for the cohesive elements in the soil matrix and at the soil-rock interface are determined. A mesoscopic numerical method for soil-rock mixtures based on the cohesive model is then established. Based on this, biaxial compression numerical tests on soil-rock mixtures with varying mesoscopic structures were conducted. The influence of different mesoscopic factors on mechanical properties was clarified by analyzing the failure state of cohesive elements. Results indicate that the maximum nominal stress in shear direction of cohesive elements can be determined by the peak shear stress of the load-displacement curve in direct shear tests. The maximum effective displacement is determined by one-fifth of the maximum shear displacement, and the tangential friction coefficient is calculated by the ratio of residual shear stress to normal stress. The numerical method based on cohesive elements can effectively describe the mechanical properties and deformation behavior of soil-rock mixtures, particularly for the strain softening behavior under low confining pressure.

Key words: soil-rock mixture, cohesive zone model, a mesoscopic numerical method, mechanical behavior of interface, strain softening