Shake table sliding response of a gravity dam model including water uplift pressure

Abstract

A series of shear tests and shake table sliding tests are performed on a 1.5 m high concrete gravity dam model with a smooth concrete–concrete frictional interface corresponding to a cold lift joint. The shear tests are performed with the sliding crack (a) in dry, (b) in wet, and (c) in pressurized conditions with peak water uplift pressures, P 0 , equal to 15 kPa, 30 kPa, and 45 kPa. For the pressurized condition, water was fed from a 12.5 mm hole reaching the interface. Monotonic shear tests indicate that the dry dynamic friction coefficient was approximately 15% smaller than the dry static friction coefficient. A reduction of 6 degrees is obtained between the wet and dry friction angles. However, there is a more significant 32% reduction between the wet static friction coefficients versus the wet dynamic friction coefficient. In the presence of a pressurized concrete–concrete interface, the sliding motions are initiated suddenly in a stick-slip mode as compared to wet and dry interfaces. Moreover, the high sliding velocity at the initiation of motion also promotes a reduction in friction coefficient, as explained by tribology in the presence of a thin water film at the sliding interface. The applications of sinusoidal pulse and earthquake ground motions have shown that residual sliding is larger for low frequency content signal (2 Hz) than for high frequency content signal (10 Hz). The uplift pressures reduce the vertical force resultant promoting sliding. The friction coefficients and related residual displacements are found to be sensitive to the sliding interface conditions. Uncertainties in the selection of the static and dynamic friction coefficients must be accounted for to develop a high confidence level in estimating residual sliding displacements that could take place for dams subjected to strong ground motions often of larger intensities than those used in the original design many years ago.