| With the vigorous development of water conservation and hydropower,a large number of gravity dams have been built in China,which makes important contributions to national economy.However,two important problems exist in these built dams.One is hydraulic fracturing of gravity dams,and the other is that there is much difference between the monitoring value and design value of the stress in dam heel.The two problems have aroused extensive concern of domestic scholars.In this study,the two problems are studied,and the main work and the innovation achievement are as follows:(1)Based on the finite element method,a stress-seepage-damage coupling model is proposed for the simulation of hydraulic fracturing of gravity dams.The coupling model has the following characteristics:(a)The constitutive law of this coupling model considers the strain softening characteristic of fracture process zone,damage-dependent pore-pressure-influence coefficient,stress-dependent permeability for the pre-peak stage and deformation-dependent permeability for the post-peak stage;(b)The mesh-dependent hardening technique is adopted so that the fracture energy dissipation is not affected by the finite element mesh size;(c)four coupling processes during hydraulic fracture are considered.The correctness of the coupling model is verified through the simulation of the fracturing of a square plate with an unilateral crack,three-point curved beam,1:40 model Gravity dam,Koyna gravity Dam and the hydraulic fracturing of the cylindrical concrete specimens with an embedded crack.(2)Using the stress-seepage-damage coupling model,taking Koyna gravity dam as an example,the influence of hydraulic fracturing on the crack propagation path and bearing capacity of gravity dam is studied.The numerical results show that hydraulic fracturing has a significant effect on the structural response of the dam and considering hydraulic fracturing effect,the carrying capacity of the dam is significantly reduced.Taking Huangdeng roller compacted concrete dam as an example,the influence of the position and length of the horizontal initial crack on the hydraulic fracturing under overflow is studied.The numerical simulation results show that considering the hydraulic fracturing effect,the position and length of the initial crack have a significant influence on the crack propagation process,the final trajectory and the bearing capacity of the dam.(3)Using the stress-seepage-damage coupling model,taking an concrete gravity dam as an example,the simulation of 3D hydraulic fracturing of the gravity Dam is carried out.The effect of the position of the horizontal initial crack,the length,depth and position of the vertical initial crack,the strength of the dam concrete and the temperature difference on hydraulic fracturing is studied.And the hydraulic fracturing of the dam with an inclined initial crack is also simulated.The numerical results show that the length,depth,position,the concrete strength and the temperature difference have a significant effect on hydraulic fracturing of the gravity dams.The inclined initial crack is the most prone to hydraulic fracturing and the most harmful,and the horizontal initial crack is the least prone to hydraulic fracturing.(4)On the basis of the comprehensive analysis of the monitoring data,based on the stress-seepage-damage coupling model,the software SAPTIS,which is for the multi-field coupling simulation analysis of concrete dams during the whole process,is used for the study of the variation law of dam heel stress of spillway No.2 dam section in the whole process of the dam construction and operation period.The results are in agreement with the measured results,which preliminarily explain the reasons for dam heel stress and show that the method can be used to study the real stress state of gravity dam heel. |
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