Research On Hydrogeological Features Of Steep Karst Confined Aquifer And Feasibility Of Depressurizing In Pengcheng Square Station Of Line 1 Of Xuzhou Metro

In this thesis, we take the hydrogeological features of steep karst confined aquifer and feasibility of depressurizing in Pengcheng Square Station of line 1 of Xuzhou metro as the research object. Comprehensively expounded the trend and progress of the steep aquifer and obtaining parameters by numerical method and subway dewatering in overseas and domestic, on basis of fully collecting and analysising the pertinent information and data of region hydrogeology and karst development etc in Pengcheng Square Station, we investigate the storage geological conditions and migration rules of steep karst confined aquifer systematically.Combining the results of pumping test, we take analytical method and numerical method to make sure the hydrodynamic parameters which can reflect all features of research area. And predicting hydraulic discharge under construction by multiple methods,combined with the surrounding environment of Pengcheng Square Station,evaluating feasibility of dewatering and potential impacts on environment.This study combines the results of pumping test, the steep karst confined aquifer in study area is divided into three strips by watery, from west to east, there are Mantou formation aquifer and Maozhuang-Xuzhuang formation aquifer and Zhangxia formation aquifer. By the formula of without observation well and with one observation well,we forward pumping test and discuss on the hydraulic parameters of moisture strips; we build numerical simulation model of steep karst confined aquifer by Visual Modflow, fitting and solving the hydraulic parameters of moisture strips by indirectly inverse method, and verifying the correctness of model and parameters by forwarding long-term group pumping test. Finally, we can get a series of hydraulic parameters:(1)Mantou formation aquifer: Ky=Kz=5.58m/d, Kx=0.41m/d;(2)Maozhuang-Xuzhuang formation aquifer: Ky=Kz=1.68m/d, Kx=0.45m/d;(3)Zhangxia formation aquifer:Ky=Kz=9.32m/d, Kx=0.32m/d.On basis of this conclusion, we predict hydraulic discharge under construction by hydrogeologic analogy method and groundwater dynamic method and numerical method, evaluate feasibility of dewatering in technology and potential impacts on environment. Finally,we can get an inference:(1)The hydraulic discharge of A region in Mantou formation is 13000m3/d, it belongs to difficult to drain level; The hydraulic discharge of B region in Maozhuang-Xuzhuang formation is 6000m3/d, it belongs to easy to drain level; The hydraulic discharge of C region in Zhangxia formation is28000m3/d, it belongs to more difficult to drain level.(2)According the principles and requirements of dewatering, we make an dewatering design, the results show that although the head in southeast corner of interval by mining method does not meet design requirements, we can improve hydraulic discharge of near wells to meet design requirements.(3)According existing construction design scheme of Pengcheng Square Station, we will dewater the karst groundwater up to two years, the displacement of groundwater in Xuzhou City total of 3.43×107m3, it may lead to lots of environmental problems,such as regional groundwater level drawdown and karst collapse etc.The results of this study can be used as an reference for safe construction of Pengcheng Square Station of line 1 of Xuzhou metro, and provide an important foundation of steep karst confined aquifer influence on underground engineering, it have certain theoretical and practical significances.