LAUSR

The influence of the end effect on rock strength in true triaxial compression testing was studied using a numerical approach. The influence of the intermediate principal stress (σ2) on rock strength was isolated by using the two-dimensional Mohr–Coulomb failure criterion that depends only on the major principal stress (σ1) and minor principal stress (σ3). Thus, any enhancement to the rock strength with the increase of σ2 can be attributed to the end effect. It was shown that the end effect can result in an apparent σ2 effect, as long as the coefficient of friction (μ) at the rock specimen – steel platen contacts is not zero and the specimen in the σ2 loading direction is squat. When the strengthening due to the increase of σ2 predicted by a theoretical failure criterion was added to the strengthening due to the end effect, the results were in good agreement with the observed σ2 effect from some previous laboratory tests, indicating that the observed σ2 effect in true triaxial compression testing could be ...