This study addressed the pile settlement risks to existing pile foundations and surrounding buildings caused by dewatering during “shallow-then-deep” multi-pit excavation in the core area of Jiangbei New District, Nanjing, Jiangsu Province China. Considering the complex multilayered permeable strata and confined aquifer characteristics of the site, a detailed hydrogeological and engineering conceptual model was developed. Based on pumping test results, a three-dimensional unsteady seepage and hydro-mechanical coupling numerical model was established to simulate groundwater drawdown, aquifer consolidation settlement, and pile negative skin friction under different dewatering scenarios. The results show that single deep-well dewatering within the pit can lead to significant external groundwater drawdown and risks of sidewall leakage and piping, inducing soil boiling and void formation beneath adjacent underground structures. A combined in-pit and out-of-pit “dual-controlled dewatering” with staged recharge strategy was proposed to effectively reduce hydraulic head differences and control leakage driving forces. Numerical simulations verified its feasibility in reducing settlement and negative skin friction. The findings provide theoretical and practical guidance for dewatering design and risk management in complex urban underground multi-pit excavation projects.
Southwest Jiaotong University, China (SWJTU) International Consortium on Geo-disaster Reduction (ICGdR) UNESCO Chair on Geoenvironmental Disaster Reduction
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Southwest Jiaotong University, China (SWJTU) International Consortium on Geo-disaster Reduction (ICGdR) UNESCO Chair on Geoenvironmental Disaster Reduction