Experimental study on the shearing and crushing characteristics of talus-like rock mass

Abstract

Talus-like (T-L) rock mass is a special kind of engineering material in the nature, which owns a mixed fabric of coarse rock blocks and fine grinded rock powder. The basic mechanical properties of T-L rock mass are difficult to know due to its special composition and structure. This paper carried out a series of large-scale direct shear tests on the T-L rock mass collected in site considering four normal pressure levels. The shearing characteristics and the associated block crushing phenomena were analysed. The shear strength of the T-L rock mass increased as the normal pressure increased. The T-L rock mass had a large internal friction angle but a small cohesion. The shear stress-displacement curves can be divided into three stages: material densification, shear failure and plastic flow. The T-L rock mass showed obvious dilatancy under a low normal pressure of 50 kPa, but behaved contractively when the normal pressure became larger than 50 kPa. This indicates that the T-L rock mass may have a loose mixed fabric structure, which can be easily compressed under large normal pressures. The sieving analyses showed that the grading curve of T-L rock mass shifted upwards after shearing, suggesting that external shearing under different normal pressures led to particle crushing and changed the grain composition. The particle crushing mainly happened to the grains larger than 10 mm, which caused the portion of grains larger than 10 mm to decrease and the portion of grains smaller than 5 mm to increase. Nonetheless, the portion of grains in the size range of 5-10 mm remained approximately unchanged. Three breakage indices were adopted to quantify the crushing characteristics of the testing materials, which all increased with increasing normal pressures.