Mechanical properties and damage evolution characteristics of composite rock mass with prefabricated fractures

Abstract

In this study, the influence of fractures on the mechanical properties and cracking behavior of composite rock mass was investigated by preparing rock-like specimens of composite rock mass with different dip angles of fractures using customized molds. The failure process of the sample was recorded using a camera, and the rock failure process analysis technology was used for quantitative investigation of the mechanical mechanism of crack evolution during the loading process of the sample. Based on the experimental results, the crack propagation and coalescence modes of fractured composite rock mass were analyzed, and the distribution laws of contact force chain and maximum principal stress during initial crack initiation were studied from the microscopic perspective. The results show that with the increase in fracture dip angle, when the fracture is located in hard rock, the peak strength of the specimen decreases first, then increases and then decreases. When the fracture is located in both soft rock and hard rock, the peak strength of the specimen is mainly controlled by the fracture in soft rock. The initial crack mainly occurs at the tip of the soft rock fracture, and then converges with the cracks developed at the end of the hard rock fracture through the interface. The crack propagation type and coalescence mode are affected by the joint action of the fracture dip angle and position. In total, eight crack propagation types and six crack coalescence modes were observed during the failure process. The maximum principal stress concentration area is distributed around the fracture and is “butterfly” type. With the increase in fracture dip angle, the maximum principal stress concentration area gets gradually deflected perpendicular to the fracture direction, and does not pass through the interface of soft and hard rocks. The existence of the interface prevents the transmission of stress to a certain extent.