Evaluation of strength parameters of concrete-rock interface for dam safety assessment

An intense program of assessment of safety of dams has been initiated by Ontario Hydro. Many of the existing dams are of the concrete gravity type founded on rock, with heights ranging from 10-72 m, constructed during the period 1910-1975. The methods of stability analysis of concrete dams on rock foundations used in several organizations, including Chinese organizations, the U.S Bureau of Reclamation, and the Federal Energy Regulatory Committee, are reviewed and compared. The design issues are discussed, with the shear strength of the rock-to-concrete contact identified as being critical. Laboratory tests for the measurement of the complete strength envelope for bonded contact from tensile to compressive stress region as well as for unbonded concrete have been developed. Based on the results of these strength measurements, analyses of the performance of existing dams are presented. The issue of the use of tensile strength and cohesion in stability analysis is addressed. It is shown that the well bonded contacts can sustain significant tension and neglecting the cohesion component of shear strength is, in general, unnecessarily conservative. 8 refs., 12 figs., 6 tabs