Complete Numerical Analysis And Theoretical Research Of Surge Tank

Surge Tank is a key part of hydropower station, and has huge volume and complicate load and boundary condition, which is embedded in the rock mass, so it belongs to underground structure. On the guide of two theory of underground structure analysis: load structure method and layer structure method, structural mechanics and 3-D finite element method can be used in the analysis of surge tank. In the structural mechanics method, elastic thin wall column shell and thin slab theory is used in the computation of sidewall and bottomplate, and underground frame moment distribution method is used in the analysis of sidewall and bottomplate taking into account their rigid connection. This computation method with many simplification and assumption, can not consider the special body type of surge shaft and local variation of structure load, and the bearing capacity of surrounding rock is not fully considered. As underground structure, cavern excavation will influence the stability of surrounding rock. In this thesis, the whole numerical analysis process of surge tank structure is made to study the lining working condition based on the guidance of load structure method and layer structure method theory, the regularity and difference of computation result of structural mechanics and FEM are analyzed, and the reason for the difference is analyzed to give reference to surge tank structure analysis, based on the case of the surge tank of FUTANG hydropower station in Sichuan province. The following research work has been done:1. Considering practical situation, the second stages field of surrounding rock after cavern excavation is computed by use of spatial elastic FEM with four different lateral pressure coefficients. Through analysis of computation result, stability situation of surrounding rock is clarified, the influence of cavern excavation under different lateral pressure coefficient conditions to stability of surrounding rock is obtained; and corresponding safety measure is presented to provide reference to the selection of body type, arrangement, and construction of surge tank.2. The lining is studied under different working condition based on the guidance of load structure theory and layer structure theory by structural mechanics method, spatial FEM method, and elastic mechanics method, the regularity of different computation results is analyzed; the results of FEM method and elastic mechanics method are compared, stress transfer and composition of internal force based on the result of FEM analysis is carried to make comparison of the structural mechanics computation result and FEM result, and the reason for the difference is studied fromthe analysis theory.3. The elastic resistance coefficient of surrounding rock in different depth is obtained through the inversion of FEM result, and the comparison of traditional resisting force coefficient is done to point out the limitation of traditional method. By combination of the displacement in the wholly continuous elastic model and foundation resisting force expressed in wholly discontinuous Winkler model, the power function variation regularity of coefficient k value with the depth is put forward. The parameters in the k regularity formula are estimated by least-square method, and the computation formula of elastic resistance coefficient of surrounding rock in different depth is obtained to offer reference to analogy analysis.4. The working status of lining under inspection period is studied through spatial FEM method. By the analysis of computation result for the lining under external pressure, the regularity of stress variation along sidewall is put forward. This regularity can give reference for the lining design of surge tank.