Research And Application On Deep Foundation Pit Dewatering Methods Of Nanning Basin

The stratum of Nanning basin has the typical characteristics of dual structure, the main underground aquifer is the sand-gravel confined aquifer which has the characteristics of high water table, strong permeability and high water content. At present, many foundation pit dewatering designs and the actual precipitation construction tend to have a larger difference which brings lots of problems,and there are few studies of deep foundation pit dewatering studies based on the complex hydrogeological conditions in Nanning.Combing with the Theories and project practice, this paper studys the Analytic Method and Numerical Simulation Method of deep foundation pit dewatering design with different percolation characteristics and boundary conditions, the main achievements and results are as follows:(1)Through the porous precipitation test, the testing results show that the in-situ permeability coefficient K of aquifer drawdown is43.20m/d, and the Influence Radius R is491.25m while the water level drop to9.2m, it shows that the permeability aquifer is strong and Influence Radius is greatly in Nanning basin;(2) From the statistical analysis of the dewatering project in Nanning, we should according to the single well pumping area value a井to simplify the calculation quantity of precipitation well in console model waterproof curtain foundation pit, and suggested that the Nanning basin foundation pit single well pumping area value a井is about1000～1200m2;(3) To calculate the ground settlement induced by dewatering of foundation pit in Nanning Basin Two-layer Structure Strata through layerwise summation method, while considering the more adverse soil distribution, when the water depth is4.0～5.0m, the surface precipitation induced subsidence quantity is58.73-73.42mm;(4)Combining the Nanning rail transit station of Guangxi University entrance pit field multi-well interference precipitation test, we establish a numerical model of foundation pit precipitation of Nanning basin, by fitting experimental data, the numerical simulation calculation error observation well water level and water level measured at the scene of the absolute value is about0.2m, both to achieve the very good fitting, the results show that the numerical model is suitable for Precipitation Prediction of Nanning basin Two-layer Structure Strata of foundation pit with complex boundary conditions. The study results have important practical significance and engineering value in the design of foundation pit in Nanning basin precipitation.