Study On The Failure Mechanism And Monitoring Technology Of Culvert-Dam Interfacial Erosion In Homogenous Earth-fill Dams Of Plain Reservoirs

In order to solve the problem of water shortage in some areas of China,a large number of plain reservoirs have been built in plain areas to provide water for living and irrigation.Because of its simple structure,convenient construction and reliable operation,the earth dam has become the most widely used water retaining structure in the plain reservoir.As the water retaining structure of the plain reservoir project,the earth dam is combined with the trans-dam culvert to fulfill the function of regulating and storing water in the key project of the reservoir.Dam erosion is especially dangerous because there may be no external evidence,or only subtle evidence,that is taking place.Usually a sand boil can be found,but the boil might be hidden under water.A dam may breach within a few hours after evidence of erosion becomes obvious.The essence of interfacial erosion between earth dam and trans-dam culvert is seepage failure of soil-structure interface.Therefore,this paper firstly carried out laboratory tests and numerical calculations to study the deformation conditions,hydraulic conditions and stress conditions in the seepage failure process of soil-structure interface.On this basis,interfacial erosion model test and the discrete element analysis of model test scale was carried out,and the form,scope and process of interfacial erosion were studied.Based on the indoor model test results and the distributed fiber temperature measurement technology,the seepage safety monitoring technology of the water supply tunnel in the plain reservoir was studied.The main work and innovative achievements of this paper are as follows:(1)Design the soil-structure interface seepage failure test apparatus.The interface seepage failure test was carried out,which studied the failure process of seepage failure and the changing rule of the seepage velocity.The soil-structure seepage failure showed a three-stage progressive failure as hydraulic gradient increases,i.e.the stable,transition and failure stages;(2)The direct shear test of soil-structure interface was carried out.Based on the seepage failure test results of soil-structure interface,the rules of shear stress of interface in the "stability stage" and " transition stage" were obtained;(3)Combined with the indoor seepage failure test and direct shear test,the discrete element numerical calculation model of the seepage failure of soil-structure interface was established,and the deformation and stress rules of the interface during the "failure stage" were analyzed.The seepage failure mechanism of the soil-structure interface was revealed;(4)Based on the Datun reservoir on the eastern route of the south-to-north water diversion project,the fluid-solid coupling similar materials suitable for interfacial erosion model test were prepared and the model test was carried out.The interfacial erosion scope and process were obtained,and the mechanism of the cut-off ring structure was revealed;(5)Based on the indoor model test,the discrete element numerical calculation model of the indoor model test scale was established.and the pattern of interfacial erosion was obtained.The formula for calculating the shear stress of the interface between dam and culvert was put forward by limit equilibriun method;(6)Based on the analysis of the process of interfacial erosion between the earth dam and trans-dam culvert,the distributed fiber temperature measurement test and the temperature-flow coupling numerical calculation of the fiber are carried out.The influence law of fiber thermal conductivity coefficient,heating power and velocity on the fiber core temperature of the fiber is put forward,and the seepage safety monitoring method of the plain reservoir is proposed.