Research On Surface Settlement Caused By Phreatic Dewatering In Foundation Pit Of Suspended Waterproof Curtain

With the urbanization of our country,more and more deep foundation pit projects are appearing in urban construction,and the application of foundation pit dewatering has been more and more frequent.The influence of dewatering on the surrounding surface and construction could not be ignored,improper dewatering would cause uneven settlement of the surface,formation piping into the soil,surface collapse,and would lead to differential settlement of the building,resulting in tilting,cracking.The aquifer thickness of foundation pit engineering in Nanneihuan street station of Taiyuan Metro Line 2 is large,the hydrogeological conditions and surrounding buildings are complicated,and the improper precipitation would cause great influence.This paper aimed at solving the problem of surrounding surface settlement caused by dewatering in foundation pit of suspended waterproof curtain,and taking the Nanneihuan street station as the research object,using the methods of theoretical analysis calculation,numerical simulation calculation,measured research,to obtain the law of surface subsidence.The main work was listed as follows:(1)According to the Dupuit hypothesis and the model,the mirror theory in the Hydrodynamics,the dewatering seepage funnel equation of foundation pit of suspended waterproof curtain was derived.(2)By analyzing the mechanism of surface settlement caused by dewatering,the soil layer was divided into dry and saturated areas.Based on the effective stress principle,seepage theory and one-dimensional consolidation settlement theory,combined with the dewatering seepage funnel curve,the effective additional stress and seepage additional stress were calculated respectively.And based on the principle of superposition,an amended calculation formula about the accumulation method of each layer was obtained caused by foundation pit dewatering.The calculation results were not different from the measured data,which verifies the feasibility of the calculation formula.(3)The stochastic medium theory and formation loss rate were introduced in this paper,it was considered that precipitation caused by precipitation was a random process.According to the different additional stress,the deformation settlement of microelements in the sparse and saturated regions was calculated respectively,then through the integral summation and using the superposition principle to obtain the final settlement calculation formula.Through the calculation of engineering examples,results indicate that the calculation results were similar to the measured data,and the feasibility of the formula was verified.(4)The Nanneihuan street station carried on the numerical modelling for the engineering example,using the finite difference computation software to carry on the dewatering numerical simulation computation,compared the simulation computation result with the theory calculate result,the deformation law was similar,proved the theory computation applicability.(5)Comparing the measured settlement values with the theoretical and numerical results,the deformation law was similar,and the correctness of the theoretical and numerical calculations was further proved.Theoretical calculated results,numerical calculations and the measured values showed that the maximum surface settlement caused by dewatering in Nanneihuan street station was proximity 15 m from edge of foundation pit,and the influence range of dewatering was wide,and there was still obvious settlement at 60 m from the edge of foundation pit.