A new peak shear strength criterion of three-dimensional rock joints considering the scale effects

Abstract

The scale effect is one of the important factors affecting the shear behavior of rock joints. However, the nature of the scale dependency of rock joints is still unknown. In this study, to evaluate the effect of scale on the mechanical behavior of the joint, we selected three natural surface joints with different geometries. The sizes of these surfaces were greater than 2500 cm2. The replica joints were prepared from these three surfaces with dimensions of 50 × 50 mm2, 100 × 100 mm2, and 200 × 200 mm2. Three types of materials were used with uniaxial strengths of 12.5, 26, and 35.2 MPa. In total, 90 direct shear tests were carried out on joint samples. Finally, using the results of direct shear tests on joint specimens, a criterion was proposed for estimating the shear strength of natural joints which considered the scale effect. Compared to the previous similar criteria, in the present criterion, to quantify the roughness of the surfaces, the joint surfaces were considered three-dimensional and several roughness parameters (instead of one parameter) were used to capture both first- and second-order roughness of surfaces. The scale effect was also considered the changes in the joint dimensions (in some previous similar criteria, changes in scanning resolution of the surfaces have been considered the scale effect). Furthermore, since the surfaces of artificial joints were copied from the natural joint surfaces (instead of tensile joint surfaces), it can be expected the results of the present criterion would have a better estimate of the shear strength of natural joints.