Analysis Of Earth And Rockfill Dam Seismic Reliability

Since1950s, a large number of earth and rockfill dams have been built at strong earthquake area at home and abroad. Earthquake-resistant technology on earth and rockfill is getting a growing concern.Seismic design of earth and rockfill dam was carried out on the basis of a lot of uncertainties including uncertainty of soil parameters, model parameters, model size and seismic load and so on. In the previous design, a determinate safety factor is used to measure these uncertainties which could give a rich security reserve in static calculation, but for seismic action with the nature of strong randomness, the dam with high safety factor may appear permanent damage in an earthquake. It means that PGA, predominant period and duration of seismic motion could impact on the damage extremely.This paper considers the randomness of seismic motion based on the disadvantage of traditional deterministic design method and introduces reliability index to evaluate safety of earth and rockfill dam. Moreover many reliability analysis methods are contrasted. Static reliability methods are mostly used to solve problem of material parameters uncertainty and hard to solve uncertainty of seismic load. Dynamic reliability method mainly refers to the first passage probability theory which is based on random vibration theory, but this theory is too difficult to realize its calculation process. Given this, the extreme response distribution method is introduced in this paper as an easy way to solve reliability problem. The method aims to list probability density function of some extreme response thus calculating failure probability and reliability index of the structure. The main work could be summarized as follows:(1) Based on nonstationary stochastic ground motion, a large number of seismic waves of which the PGA meets certain distribution regular are made to calculate dynamic response (acceleration response and acceleration magnification factor, safety factor and permanent deformation) of the model, and then the extreme value should be picked to list its probability distribution by statistics and probability theory. After that this paper analyze the impact of seismic parameters (magnitude, epicentral distance) on the distribution.(2) The distribution of the minimum safety factor is fitted by probability density function to calculate failure probability and reliability index and list reference values under different safety factor critical values. (3) The distribution of the vertical permanent deformation is fitted by probability density function to get the results, and then compared with the reference values in 《(Unified Standard for Reliability Design of Water Conservancy and Hydropower Projects》 for risk assessment.