| With the increasing demand for energy structure optimization and clean energy development in China,a number of high earth-rockfill dams and large reservoirs which represented by the high earth-rockfill dams have developed rapidly under the promotion of national hydropower development strategy.China has the largest number of the high earth-rockfill dams in the world and planned to build many 200 m and 300 m dams in the western region with abundant water resources.These dams are located in the western region which the seismic geological environment is complex and large earthquakes ever occured frequently.The seismic fortification intensity of the dams in the region compared to the other regions in China is higher.Therefore,it is of great significance to carry out research on seismic safety of high earth-rockfill dams which is related to national water resources security and social public security.Scientific and reasonable analysis of dynamic response and seismic risk of high earth-rockfill dam under earthquake is the key to ensure seismic safety of high dam.The seismic response analysis of high earth rockfill dam is the foundation of its seismic safety.It is the development trend to utilize the elastic-plastic model to analyze the dynamic response of high earth-rockfill dam.Performance-based seismic design can comprehensively and effectively analyze the behavior level of structures under earthquake.Therefore,it is necessary to adopt the performance-based seismic concept into the seismic safety assessment of high earth-rockfill dams.Performance-based seismic safety assessment of high concrete dams has started in China,however there is no systematic and depth study on performance-based seismic safety analysis of high earth-rockfill dams,especially for dynamic elasto-plastic analysis of high earth-rockfill dams,selection of ground motion records,quantification method of performance level and performance parameters,and seismic fragility of high earth-rockfill dams considering the uncertainty of ground motion and dam material parameters.In this paper,the performance-based seismic risk assessment method for high earth-rockfill dams is presented.Therefore,combined with the elasto-plastic model of dam material and the dynamic elasto-plastic seismic response analysis results of high earth rock dam,the seismic vulnerability and seismic risk assessment method based on performance are studied.The main contents of this paper are summarized as follows:(1)Based on the framework of generalized plastic theory,combined with the results of earth-rockfill dam experimental materials,the modulus formula reflecting the nonlinear elastic relationship of dam materials and the plastic modulus factor reflecting cyclic hardening and hysteretic characteristics are introduced.The expressions of elastic and plastic modulus of PZC model are improved,and a unified consideration of cyclic hardening,hysteretic characteristics and plastic strain accumulation characteristics is proposed.Artificial bee colony algorithm(ABC)and soil model parameter calibration program SM2D were used to determine the improved model parameters.Through the static and dynamic triaxial test simulation of Nuozhadu rockfill material and core wall gravel soil material,the improved PZC elastic-plastic model can well reflect the main static and dynamic characteristics of dam materials,so as to verify the effectiveness of the model.The improved PZC elasto-plastic model is programmed into the finite element program of S WANDYNE Ⅱ,and the dynamic elastic-plastic response of Nuozhadu high earth-rockfill dam is analyzed.This method can be used to analyze the acceleration response law and frequency domain characteristics of high earth-rockfill dams.Through the deformation time history analysis of typical points in the dam body and the research on the deformation grid deformation of the dam,the deformation characteristics of high earth-rockfill dam can be analyzed.Combined with the dynamic consolidation theory,the excess pore pressure distribution of high earth-rockfill dam is obtained,and the calculation results can better reflect the vibration response of high earth-rockfill dam.Through the sensitivity analysis of the improved PZC model parameters to the permanent deformation results of high earth-rockfill dam,it is concluded that the seven model parameters such as Mg.Mf、γD、γden、γu、Hu0、H0 have great influence on the dynamic results.(2)A method of selecting high earth-rockfill dam ground motion records based on site spectrum and seismic parameters of dam site is established.The screening conditions and the number of ground motion records are set.The 60 seismic waves that satisfy the site conditions are selected through PEER.The mean spectrum of the selected ground motion records is in good agreement with the field ground spectrum which can reflect the uncertainty of selecting ground motion.The dynamic elasto-plastic finite element analysis of Nuozhadu high earth-rockfill dam is carried out by using the finite element program SWANDYNE Ⅱ,and the deformation and seismic damage results of the earth-rockfill at home and abroad are counted.The approach to determine the quantifiable performance index and multi-level performance level of the high earth-rockfill dam is proposed.The seismic fragility method of high earth-rockfill dam based on MSA method is utilized to analyze the failure probability of dam structure under different earthquake intensity.By discussing the variation law of the average variation coefficient and standard deviation variation coefficient of the two performance parameters with the number of seismic waves,the results show that the number of local seismic waves is greater than 30 which hardly influence the dam performance index.A performance-based seismic safety assessment method for high earth-rockfill dams is established by introducing the seismic risk model of power exponent and combining with the results of seismic fragility analysis of high earth-rockfill dams.The probability of high earth-rockfill dams reaching different performance levels in the design reference period is analyzed.The calculation results show that the probability of the dam in good condition is more than 98%,which indicates that the Nuozhadu high earth-rockfill dam has good seismic performance based on deformation in the design reference period.(3)Seven model parameters with high sensitivity in the improved PZC model are selected as random variables of high earth-rockfill dam.Considering the uncertainty of dam material parameters,the Latin hypercube sampling method(LHS)is used to establish 60 randomly generated high earth-rockfill dam as seismic-structure sample pairs.The calculation results illustrate that the exceeding probability of performance level of high earth-rockfill dam is underestimated by only considering the uncertainty of ground motion.The artificial neural network(ANN)method with strong mapping ability is introduced to train and simulate the dynamic elasto-plastic analysis results of high earth-rockfill dam.The ANN model is established to replace the finite element analysis and calculation.Combined with the MSA method,the seismic fragility analysis method of high earth-rockfill dam based on ANN-MSA is proposed.Based on the seismic risk data of Nuozhadu high earth rockfill dam,the probability density function of seismic acceleration at the dam site is derived,and the seismic risk of high earth-rockfill dam is analyzed by Monte Carlo method.Combined with the uncertainty of earthquake occurrence in time,space and intensity,the seismic risk probability of Nuozhadu high earth rock dam in 10,50 and 100 years is evaluated.Through the comparison between Monte Carlo method and numerical integration method,it is found that the seismic risk of high earth-rockfill dam will be underestimated by Monte Carlo method compared with numerical integration method.Finally,combined with the results of seismic loss and damage risk analysis of high earth-rockfill dam,a performance-based seismic risk assessment method for high earth-rockfill dam is established,and the seismic risk value of Nuozhadu high earth-rockfill dam in the design period is analyzed.The results show that the seismic risk assessment values of serious damage corresponding to the relative earthquake subsidence rate of the dam crest and the crest maximum value of the horizontal displacement in the 100 year design reference period are 1.2049 and 156.74 million yuan which is in the disaster state of earthquake loss of high earth-rockfill dam. |
