Stress And Deformation Of Composite Geomembrane In Whole Basin Anti-seepage Layer Of Karst Depression Reservoir

The construction of reservoirs in karst depressions mainly faces the problem of reservoir leakage.Its leakage path is complicated and the types of seepage are diverse,making the anti-seepage work of the reservoir difficult.Composite geomembrane is widely used in reservoir anti-seepage due to its good anti-seepage performance and strong ability to adapt to deformation,but its tensile stress and tensile strain are particula r ly important for the safe operation of reservoirs.Therefore,it is necessary to study the stressstrain characteristics of the anti-seepage composite geomembrane of karst depression reservoirs.In this paper,laboratory experiments and numerical simulation are used to study the stress-strain characteristics of the composite geomembrane in the anti-seepage structure of the entire reservoir basin in karst depressions.The main work and results of the thesis are as follows:(1)Through the indoor interface friction test,the mechanical properties of the contact interface between the composite geomembrane and the natural and saturated clay and sand materials are studied.The test results show that: The shear stress-shear strain curve of composite geomembrane and different cushion materials can be roughly divided into two stages: elastic stage and plastic softening stage;The interface friction parameters of the composite geomembrane and the cushion material in the saturated state are both smal er than the interface friction parameters of the composite geomembrane and the cushion material in the natural state.As the content of coarse particles of the cushion material increases,the interface shear stress increases accordingly.(2)In this paper,the finite element software MIDAS GTS NX is used to study the effects of the interface friction parameters of different cushion materials,the inclina t io n of the bedrock surface and the material parameters of the Duncan-Chang E-B model of the clay protective layer on the stress and strain of the composite geomembrane.The research shows that the influence of the interface friction parameters of different cushion materials on the stress-strain characteristics of the composite geomembrane is much smal er than the influence of the bedrock surface inclination on the stress-strain characteristics of the composite geomembrane;The influence of K value and n value on the stress-strain characteristics of composite geomembrane in the Duncan-Chang E-B model parameters of the clay protective layer material is more obvious than the other five parameters on the stress-strain characteristics of composite geomembrane.(3)Taking the "Three Ponds Covering Three Ponds Project in Qianjiang District,Chongqing City" as an engineering example,the safety of the composite geomembrane used in the project was analyzed,and the results showed that: Among the three reservoirs,the safety factor of Baishatang Reservoir is less than 5.0,while the safety factors of Lijiaping Reservoir and Changlianchi Reservoir are both greater than 5.0,indicating that the safety factor of Baishatang Reservoir cannot be satisfied when the composite geomembrane is used for seepage control.According to specifications,the safety factor of the composite geomembrane for seepage prevention in the other two reservoirs can meet the specifications.(4)In the engineering case analysis,the Mohr-Coulomb model is used to simulate the nonlinearity of the reservoir basin.Based on the parameter sensitivity analysis,the E0/Es of the overburden-pebbles and gravel drainage bearing layer is taken as a constant value of 2.0,and the clay is protected.The E0/Es of the layer and the overburden-cla y mixed with gravel is 1.0.The vertical deformation of the reservoir section calculated by finite element method is the closest to the result of the stress area method.