New Modified Model for Estimating the Peak Shear Strength of Rock Mass Containing Nonconsecutive Joint Based on a Simulated Experiment

Abstract

In the Jennings criterion, which is commonly used to estimate the shear strength of nonconsecutive jointed rock masses, the estimated values deviate from the actual values due to the criterion failure to consider the joint undulating angle and the weakening of the mechanical properties of the rock bridge during shearing. Based on the modified Jennings criterion, this paper considers the influence of normal stress and joint continuity on the degree of weakening of the rock bridge’s mechanical parameters and presents a new correction method to further modify the Jennings criterion. The collection of undisturbed rock samples from the study area and the creation of joint(s) for laboratory testing is a cumbersome task. To overcome these limitations, a methodology to simulate the failure of jointed rock mass using the rock-like material, cement mortar, containing a single joint was adopted and its details are presented in this paper. Specifically, the direct shear tests were conducted on artificially prepared jointed rock masses with different joint continuity and undulating angles. The influence of joint continuity and the undulating angle on the shear strength of the nonconsecutive joints was studied. Then, the influence of the normal stress and joint continuity on the deterioration of the mechanical properties of the rock bridge during shearing was analyzed based on the experimental results. A new model for estimating the shear strength of a nonconsecutive jointed rock mass was proposed based on the experimental results and previous studies. The test results show that the smaller the undulating angle and the greater the penetration, the lower the shear strength of the nonconsecutive joint. Besides, the normal stress level and the joint continuity have a significant influence on the weakening of the mechanical properties of the rock bridge. When the normal stress decreases or the joint length increases, the mechanical properties of the rock bridge are significantly weakened. Compared with our estimation of the nonconsecutive joint shear strength based on the original Jennings criterion and the modified Jennings criterion, the calculation results of the newly modified Jennings criterion developed in this study are generally more consistent with the measured values, and thus, they more accurately predict the shear strength of the nonconsecutive jointed rock mass with a regular joint undulating angle.