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SUB-HORIZONTAL JOINTING CRITICAL IN FOUNDATION STABILITY

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By Michelle Blaeser – ARQ Dams

at the SANCOLD 2022 ANNUAL CONFERENCE –  

Whereas design foundation criteria call for minimum values of various parameters including the Rock Mass Rating, RMR, Uniaxial Compressive Strength, UCS, weathering etc., sliding on potential sub-horizontal joint planes in the foundation was established to be the critical failure mode at Ntsonyini Dam. The Barton and Bandis (1990) classification systems where the joint friction is based on three parameters namely Joint Roughness Coefficient (JRC), Joint Compressive Strength (JCS) and residual friction angle were used to establish the shear parameters on the sub-horizontal joints. Specific in-field mapping procedures were developed to measure the required parameters taking specific cognisance of establishing a scale free estimate of the parameters. Specific foundation stability concerns were revealed which would never have been found inadequate if the sub-horizontal joint failure mode were not identified. The in-field mapping process, estimation of the shear strength capacity and subsequent remedial measures are described in this paper.