Analytical and numerical approaches to estimate peak shear strength of rock joints

Abstract: In Sweden, there exists a large number of dams. Many of them are founded on rock masses normally affected by the presence of sub-horizontal rock fractures, which makes sliding along rock joints under the dam foundation one of the most critical failure mechanism. Various attempts have been made to relate the peak shear strength of rock joints to measurable parameters. However, the uncertainty in the determination of the shear strength of rock joints is nonetheless still significant.The main aim of this thesis is to investigate, develop and apply analytical and numerical techniques for estimation of peak shear strength of natural and unfilled rock joints. In a first step, the peak shear strength of several natural and unfilled rock joint was calculated by using surface aperture measurements from high-resolution optical scanning and a modified version of the analytical criterion previously developed by Johansson and Stille in 2014. In a second step, PFC2D was utilised to perform numerical shear tests on two-dimensional profiles selected from high-resolution optical scanning on unweathered and perfectly mated tensile induced rock joints.The results from the analytical approach show that the calculated peak shear strengths of the analysed samples are in good agreement compared with the laboratory investigations. Conversely, the obtained results from the numerical approach show lower peak shear strengths in the analysed two-dimensional profiles compared with the conducted laboratory shear tests.The analytical approach together with the advanced techniques to measure surface roughness available today, may be a possible way forward towards a methodology to determine peak shear strength of large-scale natural rock joints in-situ.

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