Numerical study on strength and failure modes of rock mass with discontinuous joints

Based on a microscopic statistical damage model, different failure criteria are introduced into a numerical code to simulate tensile breaking and compression shear failure of jointed rock subjected to uniaxial compression and biaxial compression. Influences of geometrical parameters of the joints and lateral stress on fracture patterns and mechanical behaviors are investigated. The results show that the whole failure modes consist of four types: planar failure, stepped failure, rotating-block failure and mixed failure. The planar failure and stepped failure are associated with high strengths and strains, whereas the rotational failure is associated with low strengths and strains. As the joint inclination increases, the peak strength and elastic modulus increase and then decrease. As the lateral stress increases, the failure areas expand from the middle to both ends and appreciably improve the strength, but the increasing level will reduce when the lateral stress continues to increase. The step angle of joints has great influence on the failure modes when =90°, and the failure mode changes from stepped failure to the rotational failure. The layer distance d has slight influence on the stepped failure and great influence on the rotational failure. The rock bridge length l_r does not affect the transition of the failure mode, but it affects the peak strength and failure strain of both the planar failure and stepper failure. The results may provide guidance and reference to jointed rock engineering.