Study On The Surrounding Environment Impact Caused By Foundation Excavation In Saturated Soft Clay Strata And Risk Management

The tendency for city development of underground space is overwhelming. However, deepexcavation in saturated soft clay strata Yangtze River Delta is facing more complexenvironmental conditions as well as its own strict control conditions of the strength anddeformation. How to predict the extent of the environmental impact of deep excavation beforeconstruction is extremely important. In this paper, based on the previous studies and thebackground of Nanjing Metro ventilation shaft excavation engineering, the analysis methodincluded site measurement, numerical simulation, risk management is applied. The main contentsare as follows:⑴Based on a large collection of data about the surrounding environmental impact caused byfoundation pit excavation and precipitation as well as risk management, management system isput forward via using finite element analysis to predict the degree of environmental impactcaused by foundation pit excavation unloading and precipitation, and check out risk factorspre-construction; measures are taken to control the surrounding environment impact thoughanalyzing the site measurement data and risk preventive measures during construction;comparative analysis of various research methods is used after construction.⑵Compared the analysis of the measured data with numerical simulation results, general rulesabout the deformation of diaphragm wall, stratum and structures and the fluctuations ofgroundwater level are summarized in saturated soft clay strata.⑶General workflow for risk management of deep foundation pit is summed up. The riskmanagement and its effectiveness of ventilation shaft excavation engineering is made a detailedanalysis.From this research, the main conclusions are as follows:⑴The lateral deformation of diaphragm wall is convex, the maximum value is located at0.7H(H is the excavation depth). Factors influencing the deformation include embedded depth,support of spacing and stiffness, and space-time effect etc..⑵Stratum deformation caused by foundation excavation in saturated soft clay strata is syntheticaction including excavation unloading, consolidation and ground loss. Ground surface settlementis basin-shaped, influence range from4H to5H,0~2H as the main area of influence,2H outsidethe secondary influence area, the maximum settlement is about0.6%H away from the foundationpit0.7H; The influence region of stratum’s deformation is2H in depth from the surface andaway from the foundation. Away from the pit edge2H, there’s almost no effect.⑶Through the research methods mentioned above, control measures of ground water in ventilation shaft pit excavation engineering is analyzed. The data refers that the depth and qualityof waterproof curtain is reliable because the settlement of ground surface didn’t occur to a largeland subsidence.