Finite element analysis for the shear strength appearing in in situ rock shear tests

Abstract

The mechanisms of the strength which appeared in in situ rock shear tests were examined with a finite element analysis in this paper. A set of plaster model laboratory tests simulating the in situ rock shear tests was analyzed. The plaster models were expressed initially with constant strain triangles (CSTs). Then, the displacement was imposed gradually, and each CST was replaced with a triangular element containing an embedded interface at the point when the stress in each CST reached the failure criterion of the material. The cracking patterns and the deformation obtained from the computation resembled those in the laboratory tests. The cracking pattern under each normal stress deviated from that under different conditions; and therefore, the stress path and the shear strength appeared differently under the various normal stress conditions. The relationship between the apparent shear strength and the failure criterion of the material also changed depending on the normal stress. The shear strength measured in the model tests appeared to be lower than the material strength in the lower and in the higher normal stress ranges. Such differences were thought to occur due to the influence of the stress distributions, which were not assumed, but were caused by several different cracking patterns.