Chapter 7 - Dam abutment and arch support rock block stability and seismic safety evaluation of high arch dam

Abstract

The stability of foundation rock mass at abutments is a decisive factor for concrete dam safety evaluation, especially in earthquake cases. The traditional “limit equilibrium method for rigid body” method is actually only a static analysis without considering the dynamic deformation coupling between the dam and foundation. It contains many more uncertainties and cannot reflect the actual dynamic stability behavior of the dam-foundation system at all. It is indicated that the stability analysis of concrete arch dams must be based on the dynamic interaction in terms of the deformation coupling and take the overall displacement as the deformation-controlled criterion of instability. Actually, any instantaneously exceeding-the-limit equilibrium threshold does not mean instable, but the dam may be severely damaged due to large deformation of abutment rock mass, even if it is still stable. The stability analysis of concrete dams must be based on the dam-foundation-reservoir system interaction and take the overall displacement as the deformation-controlled quantitative criterion of instability. However, to give a unique threshold displacement as the quantitative criterion of overall instability of the system is impossible due to the variety of topography and geological disturbances at dam sites as well as the type of dam. A new conception of dynamic instability of dam systems identified by the turning point of displacement responses of the whole dam-foundation-reservoir water system, instead of the traditional approach of limit equilibrium method of rigid body, is recommended. Some examples of practical high arch dams in China are provided to show the application of the proposed approach as the quantitative evaluation criterion of the limit state of dam-breach during strong earthquakes.