佛山地铁盾构隧道深厚软土地层预处理方法探究

穿越深厚软土地层的地铁盾构隧道在长期循环荷载作用下，面临不均匀沉降、结构变形超限及其引起的渗漏水、局部结构劣化等病害难题，影响隧道结构全寿命使用功能。以佛山地铁3号线工程为背景，从施工风险、环境影响、投资及运营期结构安全角度出发，对国内地铁工程常用的软土地层土体加固工法进行分析，提出采用格栅式三轴搅拌桩加固作为地层预处理措施。对2种三轴深层水泥搅拌桩加固布置方案进行数值计算分析，对比管片内力与变形差异，确定推荐方案，并通过工程实践进行验证。数值计算与现场监测结果表明： 1）盾构隧道穿越深厚淤泥层时的加固宽度应不小于拱腰外侧3 m，深度应进入下部较好持力层0.5 m左右； 2）与未加固地层相比，地基加固处理后隧道变形可减小30%~40%，结构未发生明显的应力集中。

Ground Pretreatment Method for Deep Soft Soil of Metro Shield Tunnel in Foshan

Some diseases, i.e. uneven settlement, excessive structural deformation, seepage and local structural deterioration, would occur to metro shield tunnels crossing deep soft soil under long term cyclic loading, which would affect the whole service life of tunnel structures. Hence, by taking Foshan Metro Line No. 3 for example, the reinforcement methods for soft soil commonly used in domestic metro project are analyzed from the perspective of construction risk, environmental impact, investment and structural safety in operation period; and the grille type triaxial mixing pile reinforcement technology is proposed as a pretreatment measure. Two kinds of reinforcement schemes of deep cement mixing piles with three axes are compared and selected by numerical calculation analysis; the difference between internal force and deformation of segment is compared, the recommended scheme is determined, and it is verified by field monitoring of engineering practice. The results of numerical calculation and field monitoring show that: (1) When shield tunnel passes through deep silt layer, the reinforcement width should not be less than 3 m outside the arch waist, and the depth should be about 0.5 m below the better bearing layer. (2) Compared with the unconsolidated stratum, the deformation of the tunnel after foundation reinforcement can be reduced by 30% to 40%, and there is no obvious stress concentration in the structure.