Experimental and Numerical Study on Failure Modes and Shear Strength Parameters of Rock-Like Specimens Containing Two Infilled Flaws

To investigate the influence of infilled flaws on mechanical properties and failure modes of rock masses, seven types of pre-existing infilled two-flaw specimens, which have different flaw inclination angle (α), rock bridge length (L2) and rock bridge inclination angle (β), were made from concrete. The crack coalescence process, failure modes and mechanical parameters of the specimens under triaxial or biaxial compression were studied by lab test and numerical tests, respectively. According to test results, two failure modes of specimen (shear failure, tensile–shear failure) and three rock bridge coalescence modes (tensile crack coalescence, shear crack coalescence, no coalescence) were identified. As the rock bridge length and inclination angle increase, the peak strengths of specimens also increase gradually, while the peak strengths of specimens decrease with flaw inclination angle being increase. The shear strength parameters (cohesion c and internal friction angle φ) of samples show nonlinear changes with various factors (flaw angle, rock bridge length, rock bridge angle). The particle flow code (PFC) was used to simulate the propagation process of microcracks and porosities, stress–strain curves for loading process were also obtained, numerical results are in good agreement with experimental results. The number of cracks and porosities increase rapidly in the post-peak stage, and a significant shear fracture zone was caused by cracks. This study provides a better understanding of peak strength and cracking behaviour of rock mass containing infilled flaws.