Acoustic emission and failure characteristics of cracked rock under freezing-thawing and shearing

Abstract

The acoustic emission (AE) signal characteristics and deformation characteristics of cracked rocks under shear load can characterize the degree of rock degradation under freeze–thaw (F-T) cycles. Understanding these characteristics is of great significance for preventing rock mass engineering disasters in cold regions. In view of this, the effects of F-T cycles and crack inclination angle β on rock shear characteristics were studied by carrying out F-T tests and direct shear tests of rock-like samples with different crack inclination angles. Then, combined with AE technology and digital image correlation (DIC) technology, the effects of F-T cycle and crack inclination angle β on the characteristics of AE signals and shear deformation failure characteristics at each stage of the shearing process were analyzed. The research results show that: the deterioration of shear properties mainly occurs during the first 10 cycles. The cohesion and internal friction angle of the samples are the smallest at 30° and 60°, respectively, and the shear strength is the smallest at 60°. The damage degree of F-T cycle to the cracked samples at different angles is different. The damage degree of the 0° inclination single-cracked sample is the largest, reaching 57.17%, and the 90° sample is the smallest, reaching 49.43%. The count and b-value features of AE indicated that F-T cycles attenuated the differences in AE signal features at various stages of the shearing process. When the number of F-T cycles is less than 5, the b-value of AE undergoes a change process of a small and slow rise, a small slow decrease, a sharp decrease, and an oscillating change. When the F-T cycle reaches 20 times, the AE count and b-value characteristics did not change significantly. The speckle results show that when the normal stress is 1.5 MPa, the failure mode of the sample under shear load is pure shear or tensile-shear failure. With the increase of the number of F-T cycles, the sample has a large strain area increases and tends to fail along the shear plane.