Study On Seismic Fragility And Risk For Roller Compacted Concrete(RCC)dam Under The Influences Of Compaction Quality

Most of the Roller Compacted Concrete(RCC)dams in China are located in the southwest region where with high seismic intensity.Once damaged due to earthquake,they will not only affect the safe and stable of the structure itself,but also may bring incalculable secondary disasters.Therefore,it's necessary to carry out seismic safe study of RCC Dams.Seismic safety analysis of RCC dams can be studied from two aspects: seismic fragility and seismic risk.Seismic fragility analysis predicts the probability of RCC reaching or exceeding different damage levels under seismic loads at all levels.Seismic risk analysis can analyze the economic losses,loss of life,social and environmental impacts caused by damage of RCC dams under earthquake.Therefore,the study on seismic fragility and seismic risk of RCC dams can provide a basis for seismic safety assessment and loss assessment.In the existing research,the physical and mechanical parameters of RCC are usually selected according to the design specifications,ignoring the influence of spatial variability of these parameters on the accuracy of seismic dynamic response analysis.The spatial distribution of compaction quality of RCC can represent the spatial variability of its physical and mechanical parameters.Based on the analysis of the material characteristics and construction features of RCC,the seismic fragility and seismic risk analysis of RCC dams considering the influence of compaction quality are studied in this thesis.The main research results are as follows.(1)Current evaluation models of compaction quality of RCC dams,such as multiple linear regression and back propagation neural network,cannot reveal the highdimensional non-linear relationship between compaction quality and its influencing parameters,which leads to the problems that the accuracy,generalization ability and robustness of the model need to be improved.An adaptive grey wolf optimization stochastic forest algorithm is proposed to improve the accuracy,generalization ability and robustness of the compaction quality evaluation model of RCC dam.The engineering application results show that compared with the commonly used back propagation neural network model,random forest model and multiple linear regression model,the mean square error of the proposed compaction quality evaluation model based on adaptive grey wolf optimization random forest algorithm is reduced respectively.63.4%,46.1%,and 48.8%,the correlation coefficients increased by 38.4%,14.7%,and 12.2%,respectively.(2)The seismic dynamic response analysis of RCC dams at present fails to take the influence of compaction quality into account.A mathematical relationship model between compaction degree and physical and mechanical parameters is established based on the concrete plastic damage model.And a finite element model considering the spatial variability of physical and mechanical parameters of materials is established by combining the data of concreting sequence.Then the influences of compaction quality of seismic dynamic response are studied.The engineering application results show that the seismic dynamic response of RCC dam stress,dam top displacement and damage area will increase wither the influence of compaction quality taking into consideration,which is not conducive to the safety and stability of the dam.(3)The damage index calculation and damage grade classification in seismic fragility analysis of RCC dams at present fail to reflect the damage of the dam comprehensively,and selecting the incremental step of seismic intensity in IDA method commonly used for seismic fragility analysis is difficult.An improved IDA method is proposed to carry out the seismic fragility analysis for RCC Dams.The engineering application results show that the probability of each grade failure of RCC dams under different grades of seismic loads can be analyzed by the approach proposed in this thesis considering the influence of compaction quality.(4)The existing calculation method of seismic economic loss of RCC dams fail to consider the uncertainty of economic value and the economic loss rate of different types of buildings under the impact of dam-break floods caused by extreme seismic loads has not been studied yet.A calculation method of seismic economic loss based on threedimensional dam-break flood simulation and improved blind number theory is established.The seismic risk assessment of RCC dam has been realized with carrying out the research on life loss and social environmental impact.The engineering application results show that the seismic risk of RCC dams can be quantitatively evaluated from three aspects: economic loss,loss of life and social environmental impact through the method proposed in this thesis.