以广州新白云国际机场第二高速公路北段工程SG05标Ⅰ段和Ⅱ段基坑为例,采用地下水三维数值模拟方法,分别模拟仅开挖Ⅱ段基坑和先开挖Ⅰ段基坑再开挖Ⅱ段基坑两种开挖降水工况,探究邻近已开挖基坑对于基坑降水诱发地面沉降的影响。研究表明:单基坑开挖时周围地面沉降最大值为47.8mm,双基坑开挖时地面沉降最大值为55mm,超过了地面沉降预警值50mm。故基坑开挖降水会受到邻近已开挖基坑的影响,基坑外地面沉降也会增大。鉴于此,从降水深度和基坑止水帷幕渗透性两个方面进行优化,保证基坑底部不发生突涌破坏的前提下设计含水层最佳降水深度,并保证基坑止水帷幕渗透系数低至5.0×10-6cm/s,降水后,单、双基坑外地面沉降最大值分别为15.2mm和16.1mm,与原方案相比减少了68%和71%,优化效果较好。

Taking the foundation pits of SG05 Section I and II of the North Section of Guangzhou New Baiyun International Airport Second Expressway Project as an example, a three-dimensional numerical simulation method of groundwater was used to simulate two excavation and dewatering conditions: excavating only Section II foundation pit and excavating Section I foundation pit first and then Section II foundation pit. The aim was to explore the impact of adjacent excavated foundation pits on land subsidence induced by foundation pit dewatering. Research has shown that the maximum land subsidence around a single foundation pit during excavation is 47.8mm, while the double foundation pit during excavation is 55mm, exceeding the land subsidence warning value of 50mm. Therefore, the excavation and dewatering of the foundation pit will be affected by the adjacent excavated foundation pit, and the land subsidence outside the foundation pit will also increase. In view of this, optimization is carried out from two aspects: dewatering depth and permeability of the foundation pit waterproof curtain. The optimal dewatering depth of the aquifer is designed to ensure that there is no inrush failure at the bottom of the foundation pit, and the permeability coefficient of the foundation pit waterproof curtain is as low as 5.0×10cm/s. After dewatering, the maximum land subsidence outside the single and double foundation pits is 15.2mm and 16.1mm, respectively, which is 68% and 71% less than the original plan, and the optimization effect is good.

               
                    0引言
1工程背景
1.1地质及工程地质条件
1.2降水方案
2数值模型构建
2.1地下水渗流场模型构建
2.2地面沉降分析
3降水方案优化设计
3.1降水水位优化设计
3.2基坑止水帷幕渗透系数优化
4结论