地层特性对盾构法隧道施工地表沉降的影响研究

Influence of Strata Characteristics on Ground Settlement Induced by Shield Tunnel Construction

在软土地区进行地铁隧道盾构法施工时,地表沉降很难得到有效的控制。文章通过三维有限元法模拟地铁隧道盾构法施工过程,分析了软弱土层分布对地表沉降的影响,并通过实测结果分析研究了盾构法施工中土层物理力学特性对地表沉降的影响。研究表明,软弱土层分布在地表至隧道底部以下0.23D范围内时(D为隧道外径),可对地表沉降产生不同程度的影响;其中,软弱土层分布在隧道埋深范围及拱顶0.23D范围内时,对地表沉降的影响最为严重,影响率超过9.910 3%;相同情况下,隧道轴线上方的软弱土层比下方软弱土层对地表沉降的影响更加明显,隧道轴线上方软弱土层对地表沉降的影响是隧道轴线下方软弱土层的1.5～6.35倍;地表沉降最大值分别随盾构断面土层压缩模量加权平均值、粘聚力加权平均值增大而减小,地表沉降最大值与土层内摩擦角加权平均值无明显关系;沉降槽宽度系数i随土层内摩擦角加权平均值增大而减小,与土层压缩模量加权平均值、粘聚力加权平均值无明显关系。

It is difficult to effectively control ground surface settlement during shield construction of metro tunnels in soft soil area.Based on a 3-D numerical analysis on shield tunnel construction,influence of soft soil distribution on ground settlement induced by shield tunnel construction were discussed.Influence of physical and mechanical behaviors of soil layer on ground settlement was verified by analyzing measurement data.The results show that ground settlement is affected to different degrees when soft soil layer is distributed from ground surface to the scope of 0.23D below tunnel floor(D is outer diameter);influence of soft soil layer on ground settlement is the largest when soft soil layer is distributed in the range of tunnel buried depth and the 0.23D at vault,with the influence rate exceeding 9.9103%;when the distance to tunnel axis is the same,the influence of soft soil layer above tunnel axis on ground settlement is 1.5-6.35 times larger than that below tunnel axis;the maximum ground surface settlement decreases with an increase of weighted averages of soil layer compression modulus and cohesion at shield section,and there is no obvious relationship between the maximum ground surface settlement and weighted average of internal friction angle;width coefficient i of settlement trough decreases with an increase of weighted average of internal friction angle of soil layer,and there is no obvious relationship among the width coefficient i of settlement trough,weighted averages of soil layer compression modulus and cohesion.