Mechanism Research Of Vacuum Tube Dewatering Method

This dissertation made studies on the major aspects of the vacuum seepage field, and the research methods and results are as follows:A field test was made based on Beijing Subway Line14project, during which several aspects of vacuum tube well dewatering including water discharge, the transfer of vacuum degree both in horizontal and vertical directions, pore water pressure and vacuum settlement were monitored to get the changing law of various indicators.The distribution law of vacuum degree was studied. Under the condition that Darcy’s law is applicable to gas seepage, the plane seepage model and Paul C. Johnson model were analyzed to understand the effects of well diameter, well chamber pressure and influence radius on the transfer law of vacuum degree.The vacuum seepage model of pore water in saturated soil was set up. Through studies combining the seepage law of gas in soil and classic groundwater seepage theories such as Dupuit theory, the changing law of water discharge, water level, water head distribution and hydraulic gradient under conditions of fully penetrating well in phreatic aquifer, fully penetrating well in confined aquifer as well as fully penetrating well in phreatic-confined aquifer was obtained and the analytical solutions were deduced further. Meanwhile, laboratory pumping experiment and numerical simulations by Modflow Software were conducted to verify the correctness of the theoretical analysis.The vacuum seepage of pore water in unsaturated soil was researched with the following results:deriving the limit conditions of gravity drainage based on analysis of the stress state of pore water; working out the influencing mechanism of gas supplement on pore water discharge based on analysis of seepage conditions of pore water in unsaturated soil and verifying the mechanism by experiment; proposing the view that takes the air entry value as the influence radius of vacuum seepage field; and making solutions of the one-dimensional horizontal vacuum seepage model of pore water in unsaturated soil using Finite Difference Method.The settlement model under vacuum seepage condition was set up. According to the transfer law of vacuum degree and water level distribution model under vacuum field, settlement calculations under vacuum were discussed considering only water declining condition. Furthermore, several models under vacuum conditions were established including Imai model, Chai J C model, elasticity model and saturated soil seepage effective stress model.The settlement under vacuum tube well dewatering was forecasted based on analysis of the settlement data of vacuum dewatering field test using Regression, Gray Theory Model GM (1,1) and BP Neural Network.The vacuum seepage law and dewatering method of interlayer water were discussed with conclusions of3distribution forms of interlayer water including horizontal, sag and inclined distribution and the construction method when vacuum wells operate uphill under the condition of inclined distribution of aquiclude.