| With the increasing development and utilization of urban underground space,foundation pit engineering is experiencing leapfrog development in scale,depth and difficulty,and generally presents the trend of "deep,large and complex".In areas rich in groundwater,the implementation of foundation pit engineering often involves precipitation and water stop.Therefore,it is necessary to deeply understand and analyze the characteristics of groundwater distribution and hydrogeological parameters of foundation pit site in advance,so as to provide a reliable basis for dewatering and water stop design.The reasonable design of foundation pit dewatering and water stop can ensure the smooth excavation of earthwork,prevent the surge at the bottom of the pit and reduce the impact on the surrounding environment.Taking the foundation pit project of Zuchongzhi Road Station of Suzhou rail transit line S1 as the research background,the hydraulic connection is judged and the hydrogeological parameters are solved through the on-site pumping and recharge test of(micro)confined aquifer.Using the determined hydrogeological parameters,the finite difference software is used to simulate and calculate the effect of precipitation in the pit and its impact on the environment outside the pit,and the optimization design of precipitation scheme is carried out.The influence and law of dewatering in the pit on the surrounding environment under the conditions of different water stop curtain permeability coefficient,depth and pumping capacity of dewatering well are studied.The research has certain theoretical and practical significance for the accurate determination of hydrogeological parameters of aquifer and dewatering and water stop design of foundation pit engineering.The main research results of this paper are as follows:(1)According to the data of field pumping and recharge test,the groundwater response law and the hydraulic connection between aquifers under the conditions of pumping and recharge are analyzed.And the layer ⑧1 is a weak permeable layer is judged.Different calculation methods are used to solve the hydrogeological parameters.Based on the comparative analysis of the advantages and disadvantages of various methods,the calculation idea of using the field pumping test data of micro confined and confined aquifer to inverse and improve the accuracy of hydrogeological parameters is put forward.The influence of recharge pressure on the rise effect of groundwater level is analyzed.The rise height of observation well water level increases with the increase of recharge pressure,but when the recharge pressure exceeds 0.05Mpa,the growth rate of observation well water level rise height slows down.(2)Combined with the precipitation test results,the precipitation of the drop waterproof curtain foundation pit(area Ⅰ)and the suspended water stop curtain foundation pit(area Ⅱ)of Zuchongzhi Road station is simulated and calculated by using the finite difference software Visual MODFLOW.The results show that during the precipitation of the drop waterproof curtain foundation pit,the water level in the pit decreases first fast and then slow,and the water level outside the pit hardly changes within 20 days of precipitation.It shows that the precipitation in the closed foundation pit will not affect the surrounding environment.The water level in the pit with suspended water stop curtain also decreases first and then slowly during the process of dewatering,but compared with the closed foundation pit,the decline speed slows down.The water level outside the pit decreases at a stable rate within 20 days of pumping,and the final water level drop depth is 2.0～2.6m,which has a downward trend.The foundation pit dewatering with suspended water stop curtain will have a great impact on the surrounding environment.For the foundation pit with suspended water stop curtain,the dewatering well should be arranged according to the principle of "dense and short".(3)Taking the suspended water stop curtain foundation pit(area Ⅱ)of Zuchongzhi Road station as the background,the influence of dewatering in the pit on the surrounding environment under the conditions of different water stop curtain permeability coefficient,water stop curtain depth and dewatering well pumping capacity is simulated and analyzed by using Visual MODFLOW finite difference software.The results show that with the increase of the permeability coefficient of the water stop curtain of the foundation pit,the drawdown range of the water level in the pit decreases after 20 days of pumping,while the drawdown and settlement of the water level outside the pit continue to increase.The deeper the water stop curtain is,the greater the drawdown range of the water level in the pit increases after 20 days of pumping,while the drawdown and settlement of the water level outside the pit continue to decrease,that is,the better the dewatering effect in the pit and the water isolation effect outside the pit.With the increase of the water pumping capacity of the dewatering well,the water level inside and outside the pit and the settlement outside the pit gradually decrease after 20 days of pumping.The precipitation in the pit has a great impact on the depth and range of water level drop outside the pit. |
