Poster presentation on stress conditions of laboratory shear tests in ARMA 2024

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Chai S, and Zhao Q. (2024). New insights for stress conditions of laboratory shear tests. In ARMA 58th. US Rock Mechanics/Geomechanics Symposium. https://doi.org/10.56952/ARMA-2024-0715 (Link, PDF)

Abstract

Numerous laboratory tests have been performed to investigate the shear behavior of rock discontinuities using various experimental setups. Stress heterogeneity on rock discontinuities can significantly influence the shear behavior, however, it has seldom been specified clearly. Instead, the macroscopic or average stress on the joints other than the local stress distribution was usually analyzed in most laboratory shear tests. In this study, numerical simulations considering a simple linear velocity weakening law are conducted on smooth rock joints in various laboratory setups to analyze the stress distribution before and during slip. The results show nonuniform normal and shear stress distribution in almost all the laboratory tests and significant local stress concentration near the edges of the shear surface. The estimated sample-average friction coefficient is slightly higher than the dynamic friction coefficient but lower than the static friction coefficient. Furthermore, a sudden release of the shear stress, especially near the stress-concentrated edges, can be observed in the slip phase during a stick-slip cycle. This study provides a critical review of laboratory shear tests on rock joints and contributes to our understanding of stress distribution and variation during stick-slip shear.

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