| With the continuous addition of high buildings, skyscraper and underground structure, the excavation developing to big depth, large area has already become an inevitable trend. Deep excavation which hydro geological condition is complicated must be taken into account both credible and economic timbering measures and the ground water, especially confined water, which has important effect on the deep excavation.Cities in the middle reaches and lower reaches of the Changjiang River, which reprehensive by Wuhan city, almost locate at the first terrace or the second terrace of the river. Foundation soil is distributed as typical binary structure. Because of the alluvium and diluvium, permeability coefficient between the horizontal direction and vertical direction exist big difference. Because of the limitation of the hydro geological condition, the filter pipe of pumping well is always below -25m underground when taking deep-well dewatering in the deep excavation in Wuhan city. But because of limitation of the deep of the excavation, most waterproof wall cannot reach to the depth, then in the excavation there are both horizontal and vertical seepage. Big depth of the excavation in some big project caused deep waterproof wall, then the waterproof wall can be used to stop part horizontal seepage. Horizontal seepage is partly stopped by putting the filter pipe up to the bottom of the waterproof wall, and the intensity is also weakened, which put up the augmentation of the drawdown in the condition of the fixed flux. But, the issues, such as the extent of the effect of pensile curtain on water drawdown and the relationship between the total flux and depth of pensile curtain when satisfied to the water drawdown of digging of the excavation, should be researched further.On the basis of widely analysis to the research result of the former researchers and summarization of the experience in the dewatering in deep excavation in Wuhan city, the article emphasizes the influence of the pensile curtain on the seepage by combining the practice of the dewatering in the deep excavation in the Changjiang River tunnel's shield well, and then find the relationship between the depth of the pensile curtain and the drawdown. The paper mainly includes the following parts:(1) The paper summarizes the seepage theory of dewatering in excavation, then analyses the basic conception and basic theory of the seepage of groundwater and establishes the equation of unstable seepage flow on the basis of discussion to the basic equation, continuity equation and the definite solution condition. And the paper finds rational theory, sustains for the question of dewatering and discusses some kinds of boundary condition, then describes the seepage of excavation correctly. (2)Comprehend several guiding ideologies, basic principle, achieve method and apply conditions. Priority studies the Rize Finite element method by analyzing its theory and applies conditions then keep track of the question must be noticed. The program utilize a "large-scale invigilate small-scale" mode to ascertain the compute extension. It is said that we make the excavation an equivalent big well and suppose constant water head as its boundary condition to compute influencing radius first, then compute drawdown of small extension. To resolve the problem of the distribution flux, the program reference the method used by MODFLOW, which method distribute flux by water conduction coefficient. To resolve anisotropy of soils, the paper follow the presupposition that keep the directions of coordinate axis and anisotropy consistent to reduce the difficult brought by anisotropy of soils. Besides that, the program replaces the normal circulation by element by circulation by node to reduce the memory of data.(3)Through analyzing the engineering geological conditions and hydro geological condition of Changjiang River tunnel's Wuchang shield well, the paper established a sententious geological model and compute model of the calculate area. Then confirmed the boundary condition, calculate parameter and compartmentalized girding, especially emphasize the pensile curtain of the excavation. Based on the following work, the paper calculated the seepage of the excavation by simulating the drawdown in and out of the excavation at 5 operating conditions, which depth of the pensile curtain is respectively 38m, 35m, 30m, 25m, 0m. Then compared the calculate results when the depth of pensile curtain is 38m to the data of fact monitoring. The result proved that when the bottom of pensile curtain in confined aquifer and the top of filter pipe is over the bottom of pensile curtain obvious three-dimensional seepage is produced in confined aquifer because of the effect of pensile curtain. The phenomena that the water level of the point outside of the curtain is much higher than the one inside, which distance to the curtain is the same, proved that the water level is discontinuous inside and outside of the pensile curtain. Compared with the water level when depth of pensile curtain is -38m, the water level of two measure points in the excavation raised a lot and water drawdown reduced by 12.39m～13.9m, that is to say reduced by 24.4%～36.8% when curtain is not setup. But the change of water drawdown of measure points out of excavation is small, the water drawdown reduced only by 2.46m～2.84m, that is to say reduced by 40.4%～44.0%. It is proved that when the total flux is fixed, the effect of pensile curtain on water drawdown is very remarkable, and effect on the water drawdown inside excavation is higher than the effect outside excavation.According to three-dimensional finite element simulation on the dewatering of the deep excavation of Changjiang River tunnel's Wuchang shield well, the error is small between the computed results based on three-dimensional numeric method and the actual measuring result. Numeric method can analyze the effect of pensile curtain on dewatering well, therefore it has important meaning to solve the problem of dewatering in excavation.
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