Seismic structural stability of concrete gravity dams considering transient uplift pressures in cracks

A theoretical model is developed for transient water pressure variations along a tensile seismic concrete crack with known crack wall motion history. Experimental tests are performed to validate the proposed model. Experimental and numerical results show that water can penetrate into new seismic cracks making them partially saturated over a length Lsat. The magnitude of Lsat and the total water uplift force acting on a crack wall are decreased by crack opening and increased by crack closing. The model is then implemented in a nonlinear discrete crack finite element program for seismic analysis of concrete dams. A 90 m high gravity dam subjected to two different ground accelerations is analysed. The magnitude of uplift force in the opening mode of the crack is small such that the downstream sliding safety factor (SSF) during crack opening is similar to the SSF assuming zero uplift force in the crack. Although the transient uplift force during crack closing reduces the upstream SSF, compared to a similar value assuming zero uplift force in the crack, its magnitude still remains larger than the minimum downstream SSF corresponding to the crack opening mode.