| In the long pressure water diversion system of diversion-type powerstation, surge chamber usually is build on the joint of diversion tunnel and diversion water pressure pipe in order to reduce water hammer pressure , and minish the water hammer effect and improve the working conditions of hydraulic turbines. Surge chamber which is excavated underground is called surge tank. Recently, along with the development of hydraulic powerstations, a lot of surge tanks in large size in complex geology structure has been built one after another, and the problem of surrounding rock stability during construction stage and structure safety during commissioning date is extrusive, which has became the key problem of construction period ,investment and safety of this kind of hydropower project. Surge tank is made up of surrounding rock and concrete structures. Traditional method usually simplifies the supporting structures and force, and reflect the action surrounding rock acted on the concrete structures by means of reckon in rock stress and elastic resistance, which ignores the interaction between rock and concrete structures. So the results can not reflect the operating state of the surge tank. The result computed with traditional method always different from the results with FEM. Especially for those complex surge tanks which built on complicated bed, the results can not show the operating behavior truly. Sichuan Minjiang Jiangsheba surge tank is in impedance shape with 122.4m long,9.3m wide and 58.8m high, whose surrounding rock consistes of â…£,â…¤class. Jiyu powerstation surge tank is impedance shape hybrid type with 51m high and the excavation diameter is 37.5m, and the surrounding rock is made up of eluvium and accumulative ice formation. Sangping surge tank is hybrid type with 47.75m high and the excavation diameter is 34m. According to geology, landform and concrete structures of these surge tanks, surrounding rock stability and reinforce effect are modified, the control height of excavation is limited, the operating state of the surge tank in construction stage and commissioning date are studied, the rule of the deformation and stress are opened out and the reinforcing result can be got by means of computing the stress and deformation. Lastly, the deformation and stress behavior computed by F.E.M. are compared with that of traditional method. The study shows that, on condition that the surge tank with bad geology condition excavated from top to bottom with concrete liner protect on time, the max. stress of surrounding rock appears on the excavation working condition. The control working condition of bar, bed and arc of surge tank is in running working condition. Surrounding rock plastic site appears at the top, upside and bottom of the well rock during the excavation period of the round surge tank.. However, plastic site appears at the top and upside of the boxed surge tank underground, and careful action should be adopted during the construction period. The stress and deformation of the surge tank structure are computed with 3D FEM in different working states,through which the working characteristics of the surge tank can be explicitly reflected . At the same time, according to the amount and distribution of the structure stress, the amount of reinforcing needed can be computed easily, which provides gist for the designer. For circular surge tank, the stress and deformation computed based on tradition method of liner are symmetrical around the well, which are different from the results by means of 3D FEM at the same position. However, both the stress and deformation are regular.
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