深基坑事故大多是由于地下水控制失效造成。长沙地区砂卵石地层透水性好、富水性强、水源补给充沛，地下水的影响更为明显。研究在富水砂卵石地层中深基坑开挖和水位下降引起的地面沉降、基底渗透稳定等影响与变化规律，具有十分重要的现实意义。对长沙富水砂卵石地层地铁深基坑降水与开挖施工过程进行流固耦合数值模拟，计算结果表明，砂卵石地层中基坑开挖引起的地表沉降值与沉降影响范围更大；最大沉降位置更靠近围护结构，沉降曲线表现为较陡；地表沉降速度初期较快，后期较慢；最大渗流力主要分布在连续墙嵌固深度范围内偏下处。针对长沙富水砂卵石地层深基坑特点，提出注浆封底加固，与地连墙防渗帷幕形成封闭截水的风险控制措施与建议。%Most deep foundation pit accidents are caused by the failure of groundwater control. Sand and cobble layer in Changsha is characteristic of good water permeability, water rich, abundant water supply with remarkable groundwater impact. Therefore, research on water-abundant sand and cobble layer in deep foundation pit excavation and water level decline caused by ground subsidence, basement permeability stability influence and the changing rules is of great significance. Seepage-stress coupling simulation of deep foundation pit dewatering and excavation of deep foundation pit in the Changsha water-abundant sand and cobble layer is conducted. The results show that the surface subsidence caused by foundation pit excavation in sand and cobble layer and the scope of settlement are very big; the maximum settlement position is closer to the retaining structure and the subsidence curve is steeper; the surface subsidence velocity is fast at initial stage and slow at late stage; the maximum seepage force is mainly distributed in the lower part of the partial solid point embedded in the continuous wall. According to the characteristics of deep foundation pit in Changsha water-abundant sand and cobble layer, risk controlling measures and suggestions are put forward to reinforce by bottom grouting and to form a closed cut-off wall and anti-seepage curtain.
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