Simulation Study of the Mechanical Properties of Hollow Rock Masses under Varying Aperture Angles and Confining Pressures

To reveal the fracture evolution characteristics and micromechanical mechanisms of variable-aperture hollow rock masses, hollow cylindrical samples with three types of variable-aperture angles were designed using the three-dimensional particle flow code (PFC3D version 5.0) for triaxial compression simulations. Results show that the peak value of acoustic emission (AE) counts decreases with the increase of confining pressure. Under high confining pressure, the samples exhibit multiple peaks in AE counts before the peak strength, with intense postpeak AE activity. The failure criterion of variable-aperture hollow rock mass has good applicability. Confining pressure affects the initiation stress and damage stress of the samples, promoting their failure, while the impact of variable-aperture angle on damage stress is more pronounced. The spatial distribution of cracks concentrates at the larger aperture end of the samples with increasing confining pressure. Smaller aperture angles correspond to a higher degree of fragmentation, whereas larger angles result in a greater elastic modulus and an increased likelihood of local damage. The distribution of contact forces in samples with different variable-aperture angles is basically consistent. The distribution pattern of the fabric effectively reflects the anisotropic changes of the contact force.