Preliminary study on evaluation of global safety degree of concrete gravity arch dam

According to the structural characteristics of gravity arch dams,a 3D nonlinear finite element method based on smeared-crack model is used in this paper to evaluate the global safety degree(GSD) of a gravity arch dam.The displacement mutation,plastic zone connectivity,dam failure modes and calculation convergence are suggested as criteria to estimate the safety of the concrete gravity arch dam system.Taking a domestic concrete gravity arch dam as an example,its global safety degree is evaluated by the overload of upstream water pressure method,shear strength reduction of rock method and overload of seismic intensity method.Based on the results of comprehensive evaluation we point out the weak part of the dam,and provide a theoretical basis for optimization design.The results indicate that GSD under upstream overloading water pressure is about 5.0;GSD under shear strength reduction of rock in dam foundation is about 3.5;GSD under earthquake is about 1.7.The failure modes of concrete gravity arch dam are different from the general arch dam.It may fail because of the lower dam abutment damage and the base rock yield caused by upstream overloading water pressure.With the reducing of the shear strength of rock,sliding may occur because of the base rock failure.Cracking damage,causes the failure of the dam-rock system under earthquake.It is mainly located at the dam heel and the base of the spillway pier which are considered to be the relatively weak parts under earthquake.