Numerical Study of Failure Mechanism of Serial and Parallel Rock Pillars

Using a numerical modelling code, rock failure process analysis, 2D, the progressive failure process and associated acoustic emission behaviour of serial and parallel rock samples were simulated. Both serial- and parallel sample models are presented for investigating the mechanism of rock pillar failure. As expected, the numerical results show that not only the stiffness, but also the uniaxial compressive strength of the rock plays an important role in pillar instability. For serial pillars, the elastic rebound of a rock pillar with higher uniaxial compressive strength can lead to the sudden failure of an adjacent rock pillar with lower uniaxial compressive strength. The failure zone forms and develops in the pillar with lower uniaxial compressive strength; however, the failure zone does not pass across the interface of the two pillars. In comparison, when two pillars have the same uniaxial compressive strengths but different elastic moduli, both serial pillars fail, and the failure zone in the two pillars can interact, passing across the interface and entering the other pillar. For parallel pillars, damage always develops in the pillar having the lower uniaxial compressive strength or lower elastic modulus. Furthermore, in accordance with the Kaiser effect, the stress-induced damage in a rock pillar is irreversible, and only when the previous stress state in the failed rock pillar is exceeded or the subsequent applied energy is larger than the energy released by the external loading will further damage continue to occur. In addition, the homogeneity index of rock also can affect the failure modes of parallel pillars, even though the uniaxial compressive strength and stiffness of each pillar are the same.