Study On Reliability Of Seismic Residual Deformation And Residual Strain Analysis In Rockfill Dam

The rockfill dam is widely used because of its lower cost,quick construction and foundation adaptability.Now plenty of rockfill dams have been constructed or being planned.Many of these rockfill dams located in the western region of China,where earthquake occurred frequently.The massive loss will be caused once dam breaks.Now domestic and foreign scholars have carried out a lot of the research on the numerical simulation of high rockfill dams subjected to earthquake.Namely,a number of seismic waves are chosen as input,dynamical response is analyzed,and then the seismic safety of rockfill dam is evaluated according to evaluation criterion.However,the evaluation criterion is determined based on lots of engineering experience,which is still no general consensus.In addition,there exists a lot of uncertainty factors in the seismic response analysis of rockfill dams,the deterministic analysis cannot reflect the effect of uncertainty factors.Reliability analysis method quantitatively assess the uncertainty factors and take failure probability as standard.Therefore,it is necessary to evaluate the seismic failure probability of high rockfill dam based on the risk probability,which has broad application prospects.Post-seismic evaluation is crucial to the safety operation.At present,the post-seismic evaluation of rockfill dams is mainly by field investigation and monitoring earthquake deformation.These research is significant to realize the catastrophe behavior and failure mechanism of high rockfill dams,but these research are based on qualitative analysis,which cannot reflect the local deformation characteristic.Strain is an effective state parameter to assess the deformation characteristics of materials.Strain-based failure criteria are more rational to use for geotechnical materials.Thus,the strain field is suitable for describing the local damage in rockfill dams,which is helpful to analyze the seismic damage features and reveal failure mechanism.In order to solve the above problems,experimental study on dynamic deformation behavior of rockfill materials,seismic reliability analysis of high rockfill dams,strain analysis of high rockfill dam based on prototype monitoring data were studied.The main contents on these research are as follows:(1)Large scale cyclic simple shear tests on rockfill materials of Gushui limestone were performed to study the characteristics of dynamic moduli,damping ratios and residual deformations.The experimental results show that the curves of Gd/Gdmax～γy andλ/λmax-γd were described by the modified nonlinear viscoelastic dynamic constitutive model.When the confining pressure and dynamic stress ratio are higher,the relationship between residual strain and numbers of cyclic diverges the semilog rule evidently.Based on the test data,a power function was adopted to describe the development of residual strain.Then a residual strain model is proposed,which is a function of the average main stress,consolidation ratio and dynamic shear strain.By analyzing the collected test results,the feasibility of this model is validated.(2)Based on the seismic intensity probability model,the earthquake intensity occurrence probability and factor are determined.Considering the uncertainty of dam materials,φ andΔφ are chosen as the uncertain parameter,the statistical characteristic is obtained by analyzing the experimental parameter of rockfill dams above 100m.As the most dangerous slip of dam slope needs iterative search,Gaussian process regression(GPR)model is used to build the nonlinear mapping relation between seismic response and the mechanical parameters of dam materials.Then,Monte-Carlo Simulation method are employed to calculate seismic failure probability.This method was applied to calculate the seismic failure probability of the Zipingpu concrete face rockfill dam based on slope stability.(3)The seismic settlement ratio is adopted as the safety assessment index of rockfill dams.Firstly,considering the uncertainty of earthquake,the seismic acceleration corresponding to the earthquake intensity occurrence probability serve as input.Then,the parameters of Gd.max and Shen-zhujiang model are chosen as random variable,which are determined with principle of variance transfer and chi-square test.As the dynamic Finite Element Analysis of rockfill dams call for high calculation cost,Gaussian process response surface is used to build the nonlinear mapping relation between seismic response and the mechanical parameters of dam materials.Then,Monte-Carlo Simulation method are employed to calculate seismic failure probability.This method was applied to calculate the seismic failure probability of the Zipingpu concrete face rockfill dam based on seismic settlement ratio.(4)The analysis of prototype monitoring data is the straightforward and effective method to study the seismic failure mechanism of rockfill dams.At present,the analysis for prototype data is limited to qualitative description at displacement level.Therefore,a meshless smoothing method is proposed,a set of programs are developed for strain analysis of prototype dam.In this method,the Lagrange multiplier is used to establish the target functional,the optimum smoothing parameter is calculated with generalized interaction verification,then smooth and continuous displacement and strain field is obtained.For verification,this meshless smooth method was applied to calculate the residual strain of the Zipingpu concrete face rockfill dam,which was hit by the Wenchuan earthquake in China.Then,the reason of earthquake damage was analyzed,and some seismic optimization measures are proposed.In addition,the residual strain fields of the Zipingpu CFRD based on prototype data is compared to that based on FEM simulation,then the problem involved in seismic deformation simulation of high rockfill dams is discussed.