Reliability Analysis For The Gravity Dam

Gravity dam engineer is one of the key structures of hydropower and water conservancy projects because of its simple calculation principle and wide geological types.Antisliding stability is the research focus in the safety design of gravity dam,and its main analysis methods are safety factor method,limit state design method and reliability theory.Allowable safety factor design is widely used in anti-sliding stability analysis of gravity dams.However,the current water conservancy industry standard "Code for design of concrete gravity dams(SL319-2018)" provides the allowable safety factor of gravity dam engineering.In this standard,the allowable safety factor is 3.The allowable safety factor is determined by engineering experience,which is lack of physical meaning and cannot be used to evaluate the damage risk.It is found that the safety factors of many existing gravity dams are lower than the allowable values,which indicates that the allowable safety factors specified in the design specifications are not universally applicable."Code for design of concrete gravity dams(Nb / T 35026-2014)" introduces the limit state design method to solve the safety problem of anti-sliding stability.This method simplifies the complex reliability theory and applies it to engineering practice.And it can evaluate the failure risk,which is more scientific than the safety factor method.However,there are still some problems in the value of partial coefficient.In order to improve the rationality of safety factor and partial factor,this paper considers two failure modes of gravity dam: sliding mode along dam foundation and deep sliding mode,and gives the recommended values of allowable safety factor and partial factor.The main work is as follows:(1)This article provides a simple method of calibrating safety factors based on reliability theory.The calibration procedure includes:(i)First,the uncertainties in gravity dam are identified;(ii)Second,a representative set of dam cases are generated;(iii)Third,a statistical relation between safety factor and reliability index is obtained.(iv)Fourth,a90% guarantee ratio is used to link the allowable safety factor with the target reliability index.Through the calibration,it can be concluded that even for assuring a same target reliability index,higher dam should have higher safety factor.And Eight typical projects in China are selected to prove the rationality of the recommended allowable safety factor.(2)This paper upgrades the safety factor calibration theory to the partial calibration theory.A group of special gravity dam group is still selected to generate the distribution of reliability index,which is used to represent the actual safety level of different partial factor groups.The 90% guarantee rate is used to estimate the target reliability index,and a special index is introduced to judge the optimal partial factor array to obtain the calibration results.By comparing the calibration results of specifications and other literatures,the rationality of partial factors is verified.