A modified JRC-JCS model and its applicability to weathered joints of granite and quartzite

Abstract

The shear strength of rock joints plays a key role in controlling rock mass behaviors. As the ongoing process of weathering in nature brings about intricate changes to rocks, shear behavior of rock joints is also influenced by the degree of weathering of the joint surface materials. However, efficiencies of the common and simple JRC-JCS models existing in the literature in predicting the shear strength with reference to weathering grades of rock joints does not seem to have been evaluated. In this study, a modification of the JRC-JCS model was proposed based on a total of 119 direct shear tests performed on natural, planner, unfilled and weathered (i.e. grades II and III) joints of granite and quartzite from India. Subsequently, the efficacies of the proposed criterion and three other apparently useful JRC-JCS models including Barton’s model were evaluated in estimating the peak shear strength of rock joints with reference to a particular weathering grade as well as in regard to different weathering grades considered together. For such evaluation, the peak shear strength values with reference to weathering grades of the joint surfaces obtained from the direct shear tests of this study were considered. Additionally, the peak shear strength data for weathered non-planar granitic joints (i.e. grades I, II and III) existing in the literature was also taken into account. From the statistical comparison, it became evident that the shear strength criterion proposed in this study is significantly more efficient than the other considered criteria. The apparent superiority of the proposed criterion over the three other considered JRC-JCS models could be attributed to very different types of joint surfaces investigated in this study with reference to weathering grades and rock types.