Fracturing responses, mechanical behaviors and anchoring effects for rough layered rock mass

Abstract

This study is based on indoor experiments using PFC2D to conduct numerical tests on the uniaxial compression of layered rock masses with multiple sets of parallel rough joints at a loading rate of 0.1 m/s. The layered rock mass is composed of hard matrix and weak interlayer, with uniaxial compressive strengths of 45.43 MPa and 16.08 MPa and elastic moduli of 4.47 GPa and 3.20 GPa, respectively. This study numerically investigated the influences of bedding inclination α (0°–90°), joint roughness coefficient JRC (0–19.55) and anchor bolts on crack propagation, fracturing responses, crack initiation stress, mechanical properties, ultimate failure modes, and brittleness index for the rough layered rock mass. The results show that, with an increasing bedding inclination, the peak strength of the layered samples exhibits a “U”-shaped variation trend, first decreasing and then increasing. For the bedding inclination = 30°–75°, the peak strength increases with an increasing JRC. The failure modes of the sample are mainly influenced by the bedding inclination. For the bedding inclination = 0°–30° and 90°, the samples mainly experience tensile splitting failure. For the bedding inclination = 45°–75°, the samples undergo shear slip failure along the weak interlayer. The crack initiation stress of the layered samples first decreases and then increases with an increasing bedding inclination and increases with an increasing JRC. The peak strength and failure mode of the samples are both functions of the bedding inclination and JRC. Based on the different failure modes, a nonlinear strength failure criterion for the layered rock masses with multiple sets of parallel rough joints is established. Comparison with the experimental results shows that this criterion can better reflect the mechanical properties of layered rock masses. Anchor bolts can effectively increase the peak strength, reduce the brittleness characteristics, and restrict the shear slip deformation for the samples. The peak strength increases by 18.03–26.21% with an increasing initial anchoring force (0–20 MPa). When the anchoring force is 10 MPa, the peak strength of the anchored samples decreases first and then increases regarding the bedding inclination. Compared with the unanchored samples, the peak strength increases by 9.44–42.13% and the brittleness index decreases by 18.58–72.44%. The peak strength of the anchored samples increases with JRC. Compared with unanchored samples, the peak strength increases by 14.72–26.21%, while the brittleness index decreases by 69.05–73.19%.