深厚淤泥土深大基坑群同步开挖对紧邻建筑的影响

Influence of Synchronous Excavation of Deep and Large Foundation Pits with Deep Silt Soil on Adjacent Settlement-Sensitive Buildings

超大型基坑群工程开挖过程中的群坑耦合效应对土体变形和构建筑物的影响极大,且在深厚淤泥层等软弱地层中施工时其影响程度更加剧烈。因此在含深厚淤泥土的深大基坑群工程中选取适当的开挖顺序对降低保护区的土体扰动有着重要意义。依托于深圳某复杂深大基坑群工程,通过有限元三维数值模拟,探究了两侧基坑群5种不同施工方案对围护结构和敏感建筑的影响。结果表明:由于淤泥、淤泥质土等具有高流变性、高压缩性,土体水平位移较相邻上下土层产生了突变,于C区西南方向侧墙中下部分达到最大,为4.46 mm~7.01 mm,东南方向地连墙水平位移为2.67 mm~5.00 mm;当敏感建筑物周边有多个基坑时,深长基坑与保护区相邻小基坑同步开挖可进一步降低沉降敏感建筑所在场地的竖直位移,较原开挖顺序降低了31.7%;先开挖深长基坑再对小坑进行施工的工况开挖完成时围护结构侧移最小,但在对拉锚索连接的情况下同步开挖深长基坑与相邻基坑可降低群坑的时间效应,可进一步协调和控制基坑长时间施工后的最终变形。

The coupling effect of group pit in the excavation process of super large foundation pit group has a great influence on soil deformation and building structure,and its influence degree is more intense when it is constructed in soft strata such as deep silt layer.Therefore,it is of great significance to select the appropriate excavation sequence in the deep foundation pit group project with deep silt soil to reduce the soil disturbance in the protected area.Based on a complex deep foundation pit group project in Shenzhen,the influence of five different construction schemes on the retaining structure and sensitive buildings on both sides of the foundation pit group was explored through finite element three-dimensional numerical simulation.The results show that due to the high rheology and high compressibility of silt and muddy soil,the horizontal displacement of soil has a sudden change compared with the adjacent upper and lower soil layers.It reaches the maximum in the middle and lower part of the side wall in the southwest direction of area C,which is 4.46 mm~7.01 mm,and the horizontal displacement of the diaphragm wall in the southeast direction is 2.67 mm~5.00 mm.When there are multiple foundation pits around the sensitive building,the synchronous excavation of the deep foundation pit and the small foundation pit adjacent to the protected area can further reduce the vertical displacement of the site where the settlement sensitive building is located,which is 31.7%lower than the original excavation sequence.The lateral displacement of the retaining structure is the smallest when the excavation is completed under the condition of excavating the deep and long foundation pit first and then constructing the small pit.However,the synchronous excavation of the deep and long foundation pit and the adjacent foundation pit can reduce the time effect of the group pit,and further coordinate and control the final deformation of the foundation pit after long-term construction.