Numerical Simulation Of Crack Propagation In Concrete Gravity Dams Based On The Finite Fracture Mechanics

In practical engineering, no matter how rigorous control measures are taken, the concrete gravity dams still work with crack and the crack will reduce the bearing capacity of the dam. Dam heels are weak positions in the dam where cracks can not be resisted. The cracks in dam heels are classified as the interface crack, which have complex stress singularity powers. With water permeating the crack, singular stress field of dam heels becomes more complicated and the crack propagation is accelerated, which deteriorates structure stability. Therefore, the dam safety problems caused by cracks, especially by the cracks in dam heels are always the concern of scholars.Finite Fracture Mechanics believes that crack growth takes place during a very short time interval rather than during an infinitesimal period of time. Based on this assumption, hybrid fracture criterion is proposed. Within the framework of Finite Fracture Mechanics, hybrid fracture criterion puts forward that when the energy release rate and the maximum circumferential stress reach the critical value simultaneously, the crack instability propagation will be generated. Scaled Boundary Finite Element Method (SBFEM) is a method which has combined the advantages of Finite Element Mechanics and Boundary Element Method. The advantages of SBFEM are that it can get semi-analytical solution of both the stress field and displacement field around crack tips, the high accuracy solution can be obtained without enrichment around the crack tips, and by combining polygon element technology, the workload of remeshing can be minimized.Based on Finite Fracture Mechanics and Scaled Boundary Finite Element Method, this paper proposes a numerical model of the interface crack propagation under load actioa Through applying the proposed model, the stress and displacement in the radial direction can be analytically solved. Due to the limited step length, after determining the length and angle of extended step, only through resetting the crack tip and dividing the polygon of the original crack tip into two parts will the solution to the energy release rate be gained, which minimizes the workload of remeshing. When simulating the crack propagation, through changing the step length to make the energy release rate and the maximum circumferential stress reach the critical value simultaneously, that is, when the extended step length is the actual crack propagation length, the crack instability propagation will be generated, which has avoided arbitrariness of artificial assumptions.The availability of the model proposed by this paper is verified through simulating the mixed-mode crack propagation of four-point single-edge notched shear beam and model gravity dam. Through analyzing the curve of relations of external loads and crack mouth displacements and crack trajectories and providing the curve of extended step variation with crack propagation, the practical situation of crack propagation is better reflected.By applying the above numerical method into analyzing ICOLD concrete gravity dam, when considering the hydrostatic pressure, deadweight, overloading water pressure and water pressure inside cracks, contrasting with the numerical results of other literature, the model proposed by this paper is verified to be applicable to the actual engineering. And this paper analyzes the influence of different proportion of dam body and foundation elasticity modulus and different fracture toughness on the dam heel crack propagation. The numerical results show:1) Water pressure inside cracks is a significant factor when analyzing the dam fracture. Without considering water pressure inside cracks, the overloading pressure will be greatly increased, which overestimates the bearing capacity of the dam.2) The crack generated in the dam heel generally will horizontally propagate along the base surface for a distance, then goes deep into the rock.3) The horizontally propagating length is influenced by the dam body and rock material. The better stiffness and toughness of the rock than that of the dam body are, the longer the horizontal propagation is. When the rock is weaker than the dam body, the initial crack in the dam heel might go deep into the rock.