基于大型直剪试验的土石混合体颗粒破碎特征研究

土石混合体剪切时存在细观上的颗粒破碎现象,并对其宏观力学性质产生影响。基于此,以4种含水率的土石混合体为研究对象,通过室内大型直剪试验和筛分试验,分析土石混合体剪切后的颗粒破碎特征,并建立细观颗粒破碎与宏观力学性质的联系,从而加深对宏观力学性质的认识。研究结果表明:土石混合体剪切后的颗粒破碎较明显,可分为完全剪断型、表面破裂型和表面研磨型3类;颗粒破碎细观上表现为粗粒组含量降低、细粒组含量增加、中等粒组含量波动变化,统计上表现为级配曲线上移,宏观上表现为低含水率出现应变软化破坏、高含水率出现应变硬化破坏、中等含水率出现塑性应变破坏、剪应力–剪切位移曲线"跳跃"和强度非线性特征,本质上是颗粒间接触力作用产生应力集中的结果;颗粒相对破碎率随着含水率的降低或法向压力的增大而增大;黏聚力和内摩擦角均随着含水率的增大而呈幂函数规律降低。

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.