土钉墙支护及基坑变形数值模拟——以长沙中建梅溪湖项目为例

Numerical Simulation of Soil Nailing Wall Support and Foundation Pit Deformation—Taking the Foundation Pit Support of Meixi Lake Project of Changsha Zhongjian as an Example

摘要: 本文以长沙中建梅溪一号(3B地块)基坑工程为例，通过前期的地质调查、多方案论证，确定了初步的土钉墙支护结构和放坡挂网素喷的基坑支护方案，应用FLAC3D对支护方案模拟，模拟分析了采用土钉墙支护条件下，基坑开挖过程中基坑土体的变形及位移情况，并与现场监测数据做了对比。数值模拟结果显示当开挖到基坑底部时，基坑中上部水平位移值达到最大，剖面一为27.01 mm、剖面二26.46 mm、剖面三为28.16 mm。分别为基坑开挖深度的3.4‰、4.4‰、3.5‰，符合规范要求。开挖统一深度时，随着距离基坑边缘距离的增加，水平位移逐渐减小；沿着基坑垂直方向由上向下看，水平位移线增大达到最大之后再减小。三个剖面的最大水平位移都没有超过设计值的8 cm。所以说明理论设计的基坑形状、支护参数合理可靠。每个剖面前几步开挖后，监测点的沉降曲线形状相似，最后一步开挖后形状变化明显。剖面2和剖面3在基坑边缘基坑开挖前三、四步没有沉降，反而出现了上升的现象，但是在基坑开挖结束后，基坑边缘附近还是表现出沉降的趋势。剖面1基坑表面各测点表现出一直沉降，开挖的前四步随着距离基坑的距离增加沉降量逐渐减小，第五步开挖稳定后基坑边缘附近沉降变缓慢，而在距基坑边缘2 m左右沉降量达到最大；三个剖面最终的沉降曲线形状基本相同，类似于“勺子”状；三个剖面的最大沉降量分别为10.64 mm、3.4 mm、11.25 mm，为开挖深度的1.33‰、0.56‰、1.4‰，符合规范要求。基坑最大沉降值距离基坑边缘2 m左右。沉降量较小对周围建筑物和公路影响较小。

Abstract: In this paper, taking the foundation pit project of No. 1 Meixi (block 3b) of Changsha Zhongjian as an example, through the preliminary geological investigation and multi scheme argumentation, the preliminary soil nailing wall supporting structure and the foundation pit supporting scheme of sloping hanging net and plain spraying are determined. The FLAC3D is used to simulate the supporting scheme, and the deformation and displacement of the foundation pit soil during the excavation under the condition of adopting soil nailing wall are analyzed The field monitoring data are compared. The numerical simulation results show that when the excavation reaches the bottom of the foundation pit, the horizontal displacement value of the middle and upper part of the foundation pit reaches the maximum, Section 1 is 27.01 mm, Section 2 is 26.46mm and Section 3 is 28.16 mm. They are 3.4‰, 4.4‰, 3.5‰ of the excavation depth of the foundation pit respectively, which meet the requirements of the specification. When excavating a uniform depth, the horizontal displacement decreases gradually with the increase of distance from the edge of the foundation pit; when looking from the top to the bottom along the vertical direction of the foundation pit, the horizontal displacement line increases to the maximum and then decreases. The maximum horizontal displacement of the three sections did not exceed 8 cm of the design value. Therefore, the shape of foundation pit and supporting parameters designed by theory are reasonable and reliable. After the first several steps of excavation of each section, the shape of the settlement curve of the monitoring point is similar, and after the last step of excavation, the shape changes obviously. Section 2 and Section 3 did not settle in the three or four steps before the excavation of the foundation pit edge, but increased. However, after the excavation of the foundation pit, there was a trend of settlement near the edge of the foundation pit. The first four steps of excavation decrease gradually with the increase of distance from the foundation pit. After the fifth step of excavation is stable, the settlement near the edge of the foundation pit becomes slow, and the settlement around 2 m from the edge of the foundation pit reaches the maximum. The final settlement curve of the three sections is basically the same shape, similar to the “spoon” shape. The quantities of the maximum settlement of the three sections are 10.64 mm, 3.4 mm and 11.25 mm respectively, which are 1.33‰, 0.56‰, 1.4‰ of the excavation depth, meeting the specification requirements. The maximum settlement of the foundation pit is about 2 m away from the edge of the foundation pit. Small settlement has little impact on surrounding buildings and highways.