Particle breakage of soil-rock aggregate based on large-scale direct shear tests

In the direct shear tests on soil-rock aggregate (SRA), particle breakage occurs in micro vision, which will influence its macro mechanical properties. On this basis, the laboratory large-scale direct shear tests and sieving analysis tests are conducted for SRA with four kinds of moisture contents. The particle breakage is analyzed based on the test results, and the connection between the micro particle breakage and the macro mechanical properties is established, which can eventually deepen engineers’ understanding of macro mechanical properties. The results show that: (1) The particle breakage appears to be obvious after shear tests, which can be divided into three types, i.e. complete-cut type, surface-ruptured type and surface-grinded type; (2) In micro vision, the particle breakage is characterized by decreasing coarse particles, increasing fine particles and fluctuation content of medium particles. In statistics, for the particle breakage, the grading curve is upward and in macro aspect, “jumping” occurs in the shear stress-shear displacement curves, the strength of SRA is of nonlinear characteristics, and the SRA with low, high and medium moisture contents exhibits strained softening, strained hardening and plastic-strain failure models. In fact, the particle breakage results from the stress concentration of particles by touching with each other; (3) Either the decrease of moisture content or the increase of normal pressure will cause the ratio of particles breakage to increase; (4) Both the cohesion and the internal friction angle decrease like power function with the increasing moisture content.