Effectiveness of Matched and Mismatched Natural Rock Joints Using Experimental Direct Shear Tests

Abstract

In practice, the shear strength of joints is not only determined by the roughness, but also by the degree of joint matching. Due to alteration or movement, the joints with equal roughness might be mismatched. The matching degree of the joint is a significant factor that controls the normal closure, aperture, stiffness, hydraulic conductivity, and shear strength of the jointed rock mass. Studying the shear behavior of natural mismatched rock joints obtained from core drilling with different morphological characteristics, degrees of matching, and irregular shapes is an issue that has gained less attention due to the lack of samples and difficulty to obtain data. This study investigates the shear behavior of mismatched joints obtained from core drilling. Here, a new criterion is developed based on 35 series of direct shear tests, Barton and other classical theories, three-dimensional morphological characteristics, and matching condition of joints. To validate the proposed criterion, the estimation accuracy of the available classical models is compared with that of the new model. It is observed that the new criterion could achieve higher prediction accuracy for mismatched joints. Moreover, it is found that the average estimation error of the predicted values is reduced by considering the matching conditions.