无水砂层土压平衡盾构长距离掘进施工技术

在石家庄典型地质全断面无水砂层及无水粉质黏土与砂层组成的复合地层，土压平衡盾构掘进施工中易出现“盾构推力扭矩大、盾构出土不顺利、地表沉降量较大、刀盘螺旋输送机磨损严重、盾构掘进姿态控制不易控制”等施工难点。以石家庄市轨道交通1号线和平医院站-烈士陵园站区间施工为背景，通过盾构选型、掘进参数统计及分析，得出盾构在全断面砂层中掘进时必须向改良土体注入膨润土泥浆和泡沫，以达到改良和建摩的作用；盾构在粉质黏土和中粗砂组成的复合地层中掘进时，单独使用泡沫改良土体就能满足掘进要求，膨润土泥浆将不以改良渣土为第一目的，而以润滑为第一目的；在这种地层掘进时，不应只注重掘进是否顺利，还应保护盾构构件，因此在黏土地层和砂层的复合地层掘进时，加入水或膨润土泥浆是必要的。

Technology for Long distance Boring of EPB Shield in Dry Stand Strata

When EPB shields bore in the typical full face dry sand strata and/or composite strata consisting of dry silty clay and sand in Shijiazhuang, problems such as large thrust force, large torque, unsmooth releasing of mucks, serious ground surface settlement, serious wearing of cutterhead and screw conveyor and difficulty in shield attitude control may occur. In the paper, the type selection and boring parameters of the shields for the running tunnel from Heping Hospital Station to Lieshilingyuan Station on Line 1 of Shijiazhuang Rail Transit Project are analyzed. Conclusions drawn are as follows: 1) When EPB shields bore in full face sand strata, bentonite slurry and foams must be injected so as to condition the ground and reduce the friction; 2) When EPB shields bore in the composite strata consisting of silty clay and medium coarse sand, only foam injection is needed; 3) The fundamental target of bentonite slurry injection is not to condition the ground, but to improve the lubrication effect; 4) When EPB shields bore in such strata, attention should be paid not only to the successful boring of the shield, but also to the protection of the components and parts of the shield. Therefore, when EPB shields bore in the composite strata consisting of clay and sand, it is necessary to inject some water or bentonite slurry. 