Research On Arch Dam Shear Safety Analysis And Control Index Based On Trial Load Method

The stress control criterion of arch dam design code in China only considers the main tensile and compressive stresses of the dam body,and does not consider the shear stress.This choice is in line with the fact that China’s economic foundation is weak and the scale of arch dam project is not large in the past.In recent years,the construction conditions of arch dam projects are more complex and the safety requirements are higher.For the defective arch dam with low shear strength and the U-shaped wide valley high arch dam with different stress from the conventional arch dam,it is particularly necessary to carry out the shear safety analysis of the dam body to determine the shear safety index.In addition,the tensile stress of some arch dams seriously exceeds the standard,but they still have good operation performance.As a new index,the shear safety index is expected to make up for the limitation of the tensile stress index.Contrary to Chinese codes,American codes strictly control the shear safety of arch dams,but many arch dams in China that have been in normal operation for a long time cannot meet American control standards.Therefore,it is necessary to propose a safety control criterion for dam shear resistance that is different from the American code and suitable for China’s national conditions.In this paper,based on trial load method,the shear safety analysis model of arch dam body is established,and the following work is completed:(1)After shape optimization,17 typical arch dams with different dam height,width to height ratio and U/V river valley are proposed within the framework of current specifications.Firstly,the difference of mechanical properties is analyzed from the perspective of tension and compression stress.Secondly,the overloading failure simulation is carried out to analyze the influence of shear failure mode on different dam body overloading failure forms and dam body overloading safety.The sensitivity of shear parameters is analyzed,and the influence of strength reduction of weak structural planes such as transverse joints and construction layers on overload safety is considered to evaluate the overload safety of different examples and summarize the rules.(2)Combined with more than 20 actual arch dam projects,the shear safety coefficient of arch/beam section is determined as the control index of dam shear safety through the correlation analysis of dam overload safety degree and various parameters.The control value of shear safety factor of dam section for different dam height and river valley conditions,which is equivalent to the safety reserve of "tension/compression" failure mode in the current arch dam design code,is proposed and summarized.(3)Three typical cases of Pojia,Bailianya and Quanshui arch dams are selected to illustrate the applicability of the control index.Compare the actual operation state of the project with the evaluation results of tensile and compressive stress standards,section shear safety standards,and flexibility coefficient standards.The results show that the shear safety control index can reflect the defects of the dam body;As a supplement to the tension and compression stress control criteria,it can be especially used to judge the U-shaped wide valley high arch dam with relatively poor mechanical performance,and it will not be too strict compared with the shear safety control value of the American code;It makes up for the limitation that it is difficult to accurately evaluate the dam body safety when the local tensile stress exceeds the standard,so as to improve the existing arch dam evaluation system.