An enhanced index for evaluating natural joint roughness considering multiple morphological factors affecting the shear behavior

Accurate description of joint morphology is a key issue for understanding natural joint’s shear behavior and estimating its shear strength. Five sets of joint specimens with different morphological characteristics are shearing tested under different normal loads. These test results reveal that three factors, i.e., inclination angle, asperity height, and morphology of the joint back slope along the shear direction, significantly affect shear behavior. Considering the affecting mechanism of these three factors on joint’s shear behavior, a new index, named shear roughness coefficient (SRC), is proposed to accurately estimate the shear strength of rock joints. With the help of this new index, the classical JRC-JCS shear strength model can be extended from 2D to 3D surface of natural joint, which can improve estimation accuracy and reflect the shearing direction effect on joint’s shear strength.