A method to remove end effect for the determination of intrinsic 3D rock strength envelopes

Abstract The strength of rock or rock mass is needed for the design of mining and geotechnical engineering structures. Pioneer laboratory works stimulated the interest of developing 3D rock failure criteria with the consideration of the effect of the intermediate principal stress (σ2). However, the variability among some of the test data obtained under different testing conditions hampered the usefulness of these test data. In this study, a FEM tool is utilized to quantify platen-induced σ2 effects in the σ2 range of σ3 ≤ σ2 ≤ 1/2σ1. It is proposed that the intrinsic 3D rock strength envelopes within the range of σ3 ≤ σ2 ≤ 1/2σ1 can be obtained by excluding the end-effect-induced strength increase from the laboratory true triaxial compression test results. The proposed method is checked against laboratory test results of two types of rocks where applied stresses were kept the same with different rock-platen contact conditions. In the end, an approach to determine 3D failure envelopes in the full σ2 range of σ3 ≤ σ2 ≤ σ1 is proposed. This study offers insight into how to better interpret laboratory true triaxial compression test results for developing 3D failure criteria of rock.