Shear strength of the rock-concrete interface at Kalhovd dam
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The shear strength criteria Mohr-Coulomb is often used to calculate the shear capacity of rock-concrete interfaces due to its simplicity. However, the shear strength criterion does not consider all relevant aspects that contributes to shear strength in the rock-concrete interface, so it is believed that the criterion underestimates the shear capacity of concrete dams. Today, many concrete dams in Norway and the rest of the world do not fulfill the requirements to sliding stability. Dam owners are facing big investments to strengthening existing dams. Research on sliding stability of concrete dams is therefore still a hot topic. As new calculation tools and technology is developing, new shear strength criteria are developed. The main objective of this thesis was to study the shear capacity of the rock-concrete interface at Kalhovd dam. In addition, existing shear strength criteria were analyzed with respect to their capacity to address relevant aspects that influence the shear capacity in rock-concrete interfaces. Four direct shear tests on drilled cores from Kalhovd dam was conducted to study the shear strength at the rock-concrete interface. The samples were scanned both before and after the shear tests with the optical scanner ATOS Compact Scan 5MP in order to calculate 3D roughness parameters that were needed as input parameters in several shear strength criteria. The obtained tests results were used to evaluate the accuracy of identified shear strength criteria. At last, a case study was performed to analyze the sliding stability of a buttress at Kalhovd dam based on the result from the shear tests and knowledge gained through this thesis. The results from the shear tests on core samples from Kalhovd dam gave an average peak shear strength of 1.34 MPa, which corresponds to a peak friction angle of 69.5 . Grasselli s shear strength criterion turned out to be best suited to estimate the peak shear strength of the conducted shear tests. Mohr-Coulomb s shear strength criterion underestimated the peak shear strength with more than 50 %, and was therefore the least suitable model due to high estimation errors. The sliding stability of a chosen buttress were analyzed with three different methods. When the factor of safety was calculated based on NVE s guidelines where the maximum allowable peak friction angle of 50 were used, the factor of safety was found to be 1.18, hence, the buttress is not considered stable. When assessing the sliding stability by using the peak friction angle obtained from shear tests or by using a combination of FE-analysis and shear test results, the factor of safety was found to be 2.57 and 2.96, respectively, and the buttress is considered stable.