Abstract:For high dam rock foundation intersected by inversely dipping discontinuities such as shear zones,faults,joints,etc,it is generally considered that its deep sliding mode is wedge sliding along the weak planes. By elasticity and finite element method analysis,a critical point with zero-shear stress is found existing on the inversely dipping discontinuity due to the joint action of water thrusts and the weight of dam and foundation rock masses. The distributions of shear stresses for the two portions of the discontinuity partitioned by the critical point are quite different,with the shear stresses at the downstream portion of the discontinuity pointing to free face while the shear stresses at the upstream portion pointing deeply into the dam foundation. The location of the critical point is influenced by multiple factors,including occurrence of inversely dipping discontinuity,configuration of dam body,water level,etc. The smaller the angle of the weak plane,and the larger the water level are,the closer the location of the critical point is to the plumb line through the dam heel,and vice versa. The preliminary study demonstrates that in general,there are two deep shear failure modes for high dam rock foundation intersected by inversely dipping discontinuities:one is wedge sliding along the weak plane,the other is sliding along the combined surfaces of the subsurface soft layer and the downstream portion of the discontinuity. In the scenario where the angle of the inversely dipping discontinuity becomes relatively large (e.g.,larger than 10°),the wedge sliding along it is potentially impossible. Consequently,the combined sliding mode must be carefully considered in practical dam design. Not only can the analysis about the shear stress distribution along the inversely dipping discontinuity be used to determine the deep sliding mode of high dam foundation,but also can be taken as a theoretical basis for modification of the currently-used checking method for dam foundation stability against deep sliding.