Research On The Effect Of Hanging Water Curtain In Deep Foundation Pit Precipitation

With the acceleration of urbanization,municipal underground engineering continuously expand to the deeper.The aquifers in Beijing plain is given priority to sandy gravel stratum,which has good watery and strong permeability.In recent years,the over-exploitation of groundwater has become more and more serious.And the water levels has dropped dramatically.Therefore,the protection of groundwater resources is eyebrow peak.the sharply decrease of water level will result in the foundation pit of hazards such as ground subsidence,pipeline rupture,a serious threat to the surrounding building and structures of basic security.As mentioned above,the installation of the water stop curtain is wildly used.However,when the thickness of the aquifer is large,it is difficult or not necessary for the water stop curtain to reach the baffle plate,but it is suspended at a certain depth in the aquifer to achieve the purpose of water stoppage.In this paper,which is based on engineering examples and mainly performs the following research.By summarizing the research of predecessors' basic seepage theory and the basic principle of the finite difference method,which provide theoretical support for calculation and numerical simulation in the foundation pit dewatering.Here,the several kinds of main engineering precipitation methods and the struction of waterproof curtain are briefly listed.In addition,the application of waterproof curtain on underground diaphragm wall is emphasized.Taking the shield pit excavation engineering as an example,the geological survey of the study area and the design of the precipitation scheme are briefly introduced.Through the monitoring statistics at the site,the actual water output,water level change,and land subsidence are analyzed during the precipitation process.Based on the basic ideas of the "big-well method" and Darcy's law,the amount of water in the foundation pit under the three conditions of unset,suspended,and falling-off waterproof curtains was calculated.Combined with the water resource tax and curtain cost analysis,the pumping volume and comprehensive cost situation under three conditions were analyzed to illustrate the necessity of the use of a suspended water stop curtain.On the inside,it's subjected to Darcy's law and both of them are achieving solution in iterative algorithm.Finally,compare the measured data with the calculated values,the cause of the error is analyzed to explain the effect of the setting of the water stoppage.We can use the finite difference method in simulation software--Visual MODFLOW,and combined with the geological survey in actual engineering to numerical modeling and corresponding calculation.On the premise that the total amount of water is constant.Through the contrast between the different Settings of the water stop curtain and the no-stop water curtain condition,we analyze the change of free surface water head,relationship between the depth of the water stop curtain and the depth of the precipitation well is the change of the groundwater flow line.It is shown that in the sand pebbly stratum,the setting of water stop curtain has a very significant effect on preventing the foundation pit from entering into the foundation pit.And with the increase of depth of the water stop curtain its head down corresponding increase,but when the water stop curtain set certain depth deeper than precipitation well after the rule of increase rate slows significantly,and stop water heavy curtain to the change of the groundwater seepage.