Study On Dewatering Design Method Of Foundation Pit With Drop Waterproof Curtain In Confined Aquifer

With the development of the foundation pit engineering,and the deformation control is more and more strict,in recent years,the dewatering methods combing drop waterproof curtain with deep well points for dewatering are widely adopted in the deep foundation pit project in Wuhan.Theoretically,the drop waterproof curtain should be able to cut off the aquifer between inside and outside of the pit.However,in practice seepage often can be found in the bottom of the pit and the waterproof curtains.The existing foundation pit norm and the methods applied to dewatering design can't be used to build a dewatering design calculation model of foundation pit with drop waterproof curtain when take into account seepage.Furthermore,if this value depends entirely on the designer's engineering experience the dewatering engineering can not be designed safe and reliable or economical and reasonable.In conclusion,taking Henglong square deep foundation pit in Wuhan as an example,this paper conducts theoretical analysis,field test and numerical simulation to research the design calculation method of dewatering in confined aquifer with drop waterproof curtain.The specific studies are as follows:1.The related theories of deep foundation pit dewatering are generalized.The dewatering design methods are summarized into five types.And comparing their advantages and disadvantages,then discovered that these methods are short of accuracy or applicability.However it can be used for reference in the study.2.Based on the systematic pumping test in deep foundation pit of Henglong square in Wuhan,the seepage characteristics of dewatering in confined aquifer with drop waterproof curtain are researched,and the clues to the research for dewatering design methods are provided.The result shows that the drop waterproof curtain can not completely cut off the aquifer between inside and outside of the pit.The seepage characteristics outside of the pit are influenced by drop waterproof curtain.3.Combing theoretical analysis and field test,method of apparent parameter are provided to calculate the seepage volume,and plugging coefficient are used to evaluate the plugging effect of drop waterproof curtain.Taking Henglong square deep foundation pit as an example,preliminary design of dewatering in confined aquifer with drop waterproof curtain was carried out.It turned out that method of apparent parameter can be used to calculate the seepage volume,and the the error is small.the method can meet the practical demand in engineering better.What's more,plugging coefficient can reveal the plugging effect of drop waterproof curtain well,and provide the basis for the layout of the pumping well.4.Numerical simulation is used to select the better design scheme in initial designs and optimize the design.The results indicated that Visual Modflow can be available for foundation pit dewatering with drop waterproof curtain,and it can provides reference for the optimization design.