Empirical and mathematical formulation of the shear behavior of rock joints

In this paper, an empirical model based on an earlier model by Goodman and laboratory investigations of the shear behavior of limestone rock joints are presented. For developing such a model, a series of laboratory experiments were carried out on joint specimens under constant normal load (CNL). The model of shear behavior consists of two non-linear parts; the initial section includes the onset of shearing to the peak shear strength and the post-peak covering the behavior to the end of the shear test. Input data to the model include the peak and residual strength at the corresponding shear displacements. The proposed model shows very good agreement with the laboratory results and is capable of predicting the shear behavior of rock joints. Following the development of the empirical model, the investigations focused on the model by Saeb and Amadei (1992) and a mathematical model was proposed to consider both the shear and normal stiffness behavior of rock joints under constant normal stress and conditions. In this study, the proposed mathematical model was based on the aforesaid empirical model instead of the Goodman model. The capability of the proposed mathematical model to predict the behavior of rock joints under constant normal stiffness conditions was assessed using the laboratory results reported by Seidel and Haberfield (2002a,b). The model showed good correlation with the experimental data.