Cracking Analysis And Safety Evaluation For High Arch Dam

Cracking analysis and safety evaluation for arch dam is very difficulty, but it is necessary to engineer. In this paper, arch dam and its rock foundation have been taken as an integral coupling system. Stochastic mechanical model has been set up. The stress and displace field of arch dam have been analyzed in the paper. Some critical problem such as whether the dam crack, how the crack process, how much the probability of crack, have also been studied.In this paper, the linear elasticity constitutive and nonlinear elasticity constitutive have been used to simulate the dam concrete and foundation. The nonlinear elasticity constitutive adopts full dated scheme. If element stress state is three dimension, the constitutive adopted N.S Ottosen(1979)'s constitutive. The nonlinear index was calculated by the method that Jiang JianJing gave. If element stress state is two-dimension, Sargain's full constitutive code has been used. The nonlinear index was calculated according to the code given by H Kupfer and K.H Gerstle. If element stress state is one dimension, Sargin M's constitutive has been used. The cracking type has been judged according to the stress state. The cracking type was divided into three-dimension crack, two-dimension crack and one-dimension crack. The three-dimension crack is divided into snapped-type, patch-cracking type, and pole-cracking type, slanting-cut-cracking-type and extrusion-flue-type. An element cracked in three-dimension may transfer to two-dimension crack or one-dimension crack or collapse. In order to gain the right failure criteria of concrete and rock, many criteria are adopt in the paper. Many factors affect the dam's safety. SFEM was used to calculate the probability sensitivity to determined the base stochastic variable.The foundation of arch dam usually is layer rock base, and the depths of the layer are small, it is common that several layer rock base contact with one layer element grid. According to the geometry relation and the property of shape function, a new element kind that includes 24 nodes has been proposed to dissect the dam and foundation effectively, whose shape function are independent. In fact the element can be looked as a hexahedron divided into five small hexahedrons. It can be simulate all kind of the condition of the base and the dam. And it can be degenerate to area element that includes 12 nodes.To get maximum possible failure mode, the method according to the minimum conditioned reliability index is used. In the calculation of intersection probability, the step-by-step linearized Johnson method based on three-dimension has been proposed. It makes the process of calculation simple by only calculating the probability of two-dimension normal distribution. During the cracking process, the concrete's performance in the front of crack is nonlinear. In this paper, the related distance and Ordinary Kriging method are used to modify the material parameters. The related distance can be gain by the variogram models.To locate the position of crack accurately, the cracking trajectories are looked as local problem by substructure method, and used self-adapting FEM to calculate the model. In the paper, the independent shape function expressions in self-adapting structure of three-dimension brick element are given. An element can be dissected many times so that the element small enough to locate the position of crack. Because of the new-born-element are analogical with its father-element, the precision couldn't be affected. Area element such as triangle and quadrangle also used self-adopting element to refine for creating force vector. The mesh of dam and foundation can be modified in program automatically.Safety evaluation to arch dam couldn't meet the need of project according existing method at present. In this paper, the collapse probability is given through cracking trajectory to evaluate the safety of dam, and overload coefficients are also compared.