THE EFFECTIVENESS OF SAMPLE SELECTION METHODS IN STUDY OF SHEAR STRENGTH ANISOTROPY OF ROCK JOINTS

The anisotropy of shear strength of rock joints is of great significance to mechanical properties, deformation characteristics and stability of engineering rock masses. The selection of rock joints has an important influence on the study of joint shear strength anisotropy. To compare the effectiveness of sample selection methods, the anisotropy of shear strength was analyzed based on circular samples, square samples and rotated square samples. A natural slate joint in size of 1 m×1 m was selected as the research object, and the morphological characteristics of the slate joint were measured by 3D laser scanning method. The circular, square, and rotated square samples were obtained for comparative analysis. The results indicate that the shear area of the square sample obtained using the direct sampling method changes with the shear directions, and the circular sample can better reflect the anisotropy of the shear strength of joints. The statistical error of shear strength of square and round samples obtained by rotation sampling method is smaller than the error of the samples obtained by direct sampling method. The shear strength of rotated square sample and round sample with equal area are almost identical, and the statistical error is the smallest and the similarity is the largest exceeding 0.9987. Therefore, when the circular samples are not available, the rotated square samples with equal area can be selected to study the anisotropy of shear strength of joints. This study can provide certain help for the selection of rock joints and provide a basis for the study of the anisotropy of shear strength of rock joints.