Study On Seismic Hydraulic Fracture Of Gravity Dams Based On Scaled Boundary Finite Element Polygons

During the operation of concrete gravity dam,the phenomenon of stress concentration will occur at the dam heel and broken slope point of the upstream dam surface under the action of high water head,and it is easy to produce microcracks.If the strong earthquake occurs,these micro-cracks will propagate to the interior of the dam.At the same time,due to the increase of the crack mouth opening displacement,the reservoir water will enter the crack under the action of high head pressure,and the water pressure will play a greater role on the crack surface.The singular stress field near the crack tip is more complex and has a great influence on the crack propagation.The experimental and theoretical research on the distribution of internal water pressure and its effect on the crack propagation under dynamic conditions are far from enough.In this paper,the scaled boundary finite element method is used to study the dynamic crack propagation of gravity dam.On the basis of the coupled dam-reservoir-foundation-dynamic interaction model,the dynamic water pressure model along the crack face and the contact element,based on the generalized stress intensity factor and the Huchinson & Suo propagation criterion,a numerical model is proposed to simulate the dynamic hydraulic fracturing of interface cracks.In this model,the different material properties of dam and foundation can be considered respectively,and the stress intensity factors of each angle in the neighborhood of the crack tip can be solved efficiently.The model can obtain the propagation direction of cracks under different stress conditions.By presetting cracks on the dam face and heel,considering the gravity force of the dam body and foundation,the hydrostatic pressure and hydrodynamic of the dam surface,the water pressure in the crack and the seismic load,the dynamic fracture process of the dam face and heel is simulated in this paper.The effects of different water pressure distribution modes on the response and fracture characteristics of gravity dam are studied.The influence of hydraulic fracture of dam heel on weak joint is simulated.The evolution process and failure mechanism of hydraulic fracturing of dam heel under gravity dam-foundation system are discussed.The numerical results show that:(1)Under the action of seismic load,the water pressure distribution on the crack surface of the dam is significantly different from that under the static action,and the opening and closing mode of the crack determines the water pressure of the dam.In addition,this difference also significantly affects the response and crack propagation of the dam;(2)Crack propagation in the dam heel of gravity dam-foundation system,the dynamic water pressure and the constant seam water pressure model have high similarity.In practical engineering,it is reasonable and feasible to assume that the water pressure along the crack face at dam heel is in the form of constant distribution for the seismic analysis;(3)The propagation path of the crack starting at the heel is influenced by the fracture toughness of the concrete,rock and interface.The distance along the interface of the crack increases with the increase of toughness of concrete and rock.With the growth of the propagation length,crack tends to bend into the dam or rock,depending on the relative value of the driving force and resistance at that time.When the fracture toughness of rock is smaller than that of concrete or the fracture toughness of rock is larger than that of concrete and the difference is not big,the crack extends to the foundation.With the increase of fracture toughness difference between concrete and rock,the crack may extend into the dam.