Strength Parameters of Rock Considering Area and Stress Correction During Shearing

Abstract

Rock shear strength parameters are the basis for rock mechanics research and rock engineering applications, generally obtained by triaxial test and compression shear test method. In the current compression-shear test method, the initial shear area of the specimen is used for calculation, and the change of the shear area during the shearing process is not considered. In the actual shearing process, as the shear displacement increases, the shearing area decreases, and the compression-shearing mold has support for the shearing part of the specimen, causing the calculation error of shear stress and normal stress, so that the cohesive force error obtained by the compression shear test and the triaxial test is large. The area correction coefficient β and the support force σmj of the shearing mold for the sheared specimen were introduced, and the shear stress and normal stress on the shear surface were corrected under the conditions of rock compression shear test. According to the Mohr–Coulomb criterion, the cohesion force is obtained, and the correction formula of rock cohesion is proposed. Verification and error analysis of the proposed formula through experiments, the correction value is closer to the true value of rock cohesion and improves the reliability of the compression-shear test method. Based on the formula of the cohesion correction formula, the influence of the test factors such as the size of the specimen was discussed. It was found that the increase of the size of the specimen helps to weaken the influence of the change of the shear area on the stress.