Analysis Of Cracking Causes And Seismic Safety Of Concrete Gravity Dams

For the past 40 years,there are a lot of concrete gravity dams built in China.Most of them locates in the seismic belt and seismically active areas.Concrete degradation,design defect,poor quality construction,overloading and earthquake effects have reduced the safety of gravity dam year by year,especially difficult to withstand the action of strong earthquakes.Although the current domestic and international scientists have done much research on seismic response of gravity dam,there is little research on seismic security and operating state of long-serving gravity dam with cracks.In view of the above-mentioned factors,a concrete gravity dam in Shenwo reservoir was investigated.The seismic security and operating state of long-serving gravity dam was studied by the detection analysis,numerical simulation analysis,seismic responses,and the evaluation of operating state.In addition,crack situation and crack cause of the concrete gravity dam are also investigated.All of them will be committed to explore a set of scientific and reasonable method to assess the security of long-serving concrete gravity dam under strong earthquakes and the causes of crack.The main content and understandings obtained are as follows:Firstly,laboratory tests and field tests for concrete and steel at the spillway pier,upstream face of dam,and downstream face of side piers where crack is obvious are performed.Strength characteristics of concrete and steel are determined quantitatively by these tests,which can provide the necessary experimental basis and calculations parameters to the cracking situation,numerical simulation of cracking cause,dynamic characteristics analysis of dam,operating state of concrete dam,and the reliability of integral security of dam under strong earthquakes.Then,the macroscopic characteristics,spatial distribution,frozen and corrosion phenomenon of dam's crackings were observed,through the field investigation of dam.Furthermore,combined with the historical records about the characteristics,distribution,and the development of cracking,the causes of cracking and the influencing factors of cracking were obtained.Secondly,an effort was made to use the potential fluid to model the reservoir,the smeared crack model to simulate the generation and expansion of cracking,and the fluid-solid coupling analysis,in order to establish the three dimensional finite element modelling of dam-reservoir-bedrock against dam's operation security and security under earthquake loading.In addition,the seismic response and security of dam were also addressed.Finally,on the basis of the theory of reliability,using the advanced large-scale finite element program OpenSees,the deterministic analysis(including quasi static analysis and time history analysis)and the uncertainty analysis(including time invariant and time-varying analysis)of dam under strong earthquakes were conducted to evaluate the security of concrete gravity dam against the original state and current state of dam.