某软土深基坑降水开挖地表沉降及影响因素分析

基于某软土地铁站深基坑工程项目，依据勘察与抽水试验数据采用有限元软件Midas GTS建立三维模型，研究渗流-应力耦合作用下基坑降水开挖过程中孔隙水压力及地表沉降变化规律，分析土体渗透系数及降水深度、降水速率等设计参数对地表沉降的影响。研究表明:基坑降水开挖使得地下水渗流路径呈降落漏斗形，基坑底部出现凹弧形等孔压线；地表最大沉降点与基坑的距离约为降水深度的1.0~0.75倍，孔压消散是地表沉降的主要因素；最终降水深度每增加1 m相应地表最大沉降量增加约2 mm，采取回灌措施比未采取引起的基坑周边地表最大沉降小26.2%。

Analysis on Ground Settlement and Influencing Factors of Dewatering Deep Excavation in Soft Ground

Based on a subway station’s deep foundation pit project in soft ground，the 3D model was established by the finite element software Midas GTS relied on the survey and pumping test data. Under the seepage-stress coupling effect，the changes in pore water pressure and ground settlement during the dewatering excavation of the foundation pit were studied，and the effects of soil permeability coefficient and design parameters，such as precipitation depth and precipitation rate，on ground settlement were analyzed. The results show that the dewatering excavation of the foundation pit makes the groundwater seepage paths appear as a dropping funnel，and the concave arc pore pressure isobars appear at the bottom of the foundation pit. The distance between the maximum settlement point on the ground and the foundation pit is about 1.0 to 0.75 times the precipitation depth. Pore pressure dissipation is the main factor of ground settlement. Each increase in the final precipitation depth at 1 m，the maximum ground settlement increases by about 2 mm. The maximum ground settlement around the foundation pit caused by recharging groundwater is 26.2% smaller than that caused by no recharging.