Numerical Study of the Mechanical and Acoustic Emissions Characteristics of Red Sandstone under Different Double Fracture Conditions

Natural rock masses have many internal joints, fractures and faults, which greatly influence their mechanical properties during geological processes. In this paper, considering different joint angles and rock-bridge angles, uniaxial compression numerical tests on double-fractured red sandstone based on particle flow code (PFC) were carried out. The influence laws of the mechanics, acoustic emission (AE) and damage evolution characteristics of double-fractured sandstone under different crack geometry conditions were analysed. The results indicated that the peak stress and elastic modulus increase with increasing fracture angle. The peak stress and elastic modulus of rock samples first increase and then decrease with the increase in the rock-bridge angle, exhibiting a nonlinear distribution; when the angle beta (rock-bridge angle) is less than or equal to 45 degrees, the peak strain differs only slightly and decreases gradually with the increase in the rock-bridge angle. There are three stages in the AE evolution of fractured red sandstone: The initial emission of AE, the increase in AE and the decline in AE. The influences of different fracture angles and rock-bridge angles on the AE characteristic rule of rock samples vary. The damage evolution process of sandstone specimens with different joints can be divided into four stages: Initial damage, stable increase, accelerated development and stable damage. The fracture angle mainly affects the damage stage. The smaller the angle of the crack is, the greater the strain value in this stage. The rock-bridge angle mainly influences the damage variable evolution during the stable increase, accelerated damage development and stable damage stages.