The Analysis Of 3-D Nonlinear Finite Element And Reliability Of Underground Cavern Structure

Traditional method of safety coefficient is used widely in the analysis of hydraulic and civil engineering. Because stochastic characteristics of all factors and variables can not be considered with this method, many shortcomings of the method can not be solved by itself. Many scholars began to consider stochastic characteristics of all factors and variables in the analysis of the structures. The characteristic of structural reliability is described by structural reliability, which makes the structure design more scientific, reasonable than traditional method, and it can further reflect the essence of the question studied.At the early operation-stage many longitudinal and transversal cracks in the concrete umbrella arch of Ying xiuwan hydropower station were found. As time went on the number of the cracks increased, and the existed cracks became longer and deeper than before. With the influence of so many cracks, the strength, stiffness and stability of the umbrella arch is decreased greatly, which endangers the operation of underground power house. According to the situation of practical operation, the paper focuses on the analysis of 3-D nonlinear finite element and reliability of the underground cavern structure. At the same time, based on the analysis of the observational data of the cracks in the umbrella arch , the layout of monitoring equipments is designed.Focused on the practical situation of the underground power house, the analysisof 3-D nonlinear finite element of the typical placement block is given with Druker-Prager Criterion. The whole calculation area of the underground power house is divided into 6156 nodes and 5570 elements. The paper places the emphasis on the concrete umbrella arch. The results show two simulated faults, E229 and f115, have great influence on the displacement and the stress of the power house. The area in tension of the right part is as basically the same as that of the crack which runs through the eighth and the ninth concrete blocks. This shows the longitudinal crack is probably produced by the intension action. The stress level of both arch abutment and the circumference of the cavern is relatively high under two operating conditions: temperature-up condition and temperature-down condition, which is one of the reasons that the transversal cracks of shear-compress style are formed.At present the reliability analysis of large-sized cavern structure has become the concern of many scholars. Because of the complexity of underground cavern structure, the performance function can not be expressed by definite equations. The first-order second-moment method and its concerned methods can not be applied. Monte-Corla method needs thousands of simulation, whose practicability is doubted. The function is made by response surface method in the paper. The results show the level of the umbrella arch was relatively low. The value of the reliability index /? was 1.5-4.8. The value ft under temperature-up condition is higher than that under temperature-down condition. According to the analysis of (3, the results are line with the practical situation.According to the author's knowledge, it is the first application of response surface method to the reliability analysis of large-sized underground cavern. With the practice, the calculation of the reliability index only needs alteration of 4-5 times and the precision could meet the requirement. Response surface method can improve the efficiency of calculation. Moreover the deterministic programs of structure analysis need no amendment. The applicability of the method is widely. It can be extended to the the reliability analysis of large-sized, complex structure.The analysis result shows that the relatively low values of 3-D displacement of the cavern are regular. The deformation can not endanger the stability of thestructure. The stress level of circumference of the cavern is relatively high, especially the tension area is obvious near the longitudinal axis of the cavern. The level of compressive stress and shear str...