Numerical modeling of jointed rock samples under unconfined and confined conditions to study peak strength and failure mode

Abstract

The presence of weak planes in most rock masses reduces their strength and changes their mechanical behavior. Jaeger’s plane of weakness theory is a simple model for predicting the strength of jointed rock samples. This model proposes a U-shaped curve for the strength of the jointed rock samples. In this paper, using the discrete element method, several two-dimensional models of the jointed rock samples are analyzed, and their results are compared with Jaeger’s plane of weakness theory. According to the results, if the sample has one or two parallel joints, the strength obtained from the numerical method corresponds to the analytical model. However, if the sample has two intersecting symmetrical joints, the concentration of stress created at the vertices of the rock blocks increases the strength of the sample, In this case, the sample strength is 80% on average higher than that of the sample with a single joint. If the sample has three or four intersecting joints with an angle of 30° to each other, the strength of the sample based on numerical solution is 36% and 40% less than the theoretical solution, respectively. In this case, because the sample is divided into several small parts, the strength of the sample is reduced and less than the theoretical model. Numerical analysis provides strength and failure mode for jointed rock samples more accurately, which will certainly be useful in designing underground structures located in jointed rock environments.