盾构切削混凝土模拟试验和切削桩基施工技术

Model Test on Concrete Cutting Directly by Shield and Pile Foundation Cutting Technology

城市轨道交通盾构施工中经常遇到穿越地下障碍物(如混凝土桩、挡土结构、管渠、地下构造物等)的难题,一般采取桩基托换、拆除桩基或人工凿桩的方法进行处理,但传统处理方法具有造价高、工期长、对周边交通影响大等缺点。通过采用小直径(400mm)盾构切削素混凝土、玻璃纤维混凝土及钢筋混凝土的模拟试验,对盾构直接切削桩基施工技术的可行性进行研究,分析了盾构刀盘的改造,获取了掘进施工参数控制资料。并通过上海轨道交通7号线和10号线工程采用盾构切削钢筋混凝土桩基的实践,证明:1)盾构直接切削钢筋混凝土施工是可行的;2)盾构始发前应对刀盘进行改造,宜在面板上增加一定数量先行刀和贝壳刀;3)盾构切削桩基过程中推进速度宜慢(小于10 mm/min),盾构设定土压、推力、刀盘扭矩宜稳定;4)在盾构切削桩基过程中,应向土仓内添加润滑减摩材料,以防混凝土碎块堵塞螺旋输送机。在盾构通过后,应根据监测情况进行管片背后的二次注浆,以控制地面和建筑物沉降;5)采用盾构直接切削桩基具有施工经济、安全,对环境影响小的优点。

Underground obstacles,such as concrete piles,soil retaining structures,pipes and trenches and underground structures,are often encountered during shield boring in the construction of urban rail transit works. These pile foundations are normally underpinned,dismantled or manually cut. However,these conventional treatment methods have such disadvantages as high cost,long construction period and severe influence on the surrounding traffics. A 400 mm model shield is used to cut blind concrete,glass fiber concrete and reinforced concrete,so as to study the feasibility of pile foundation cutting directly by shields,to make analysis on the modification of cutter heads and to obtain shield boring control parameters. Furthermore,the experience of the pile foundation cutting directly by shields in the construction of No. 7 line and No. 10 line of Shanghai rail transit works is described. Conclusions drawn are as follows： 1） It is feasible to cut reinforced concrete directly by shields; 2） Before shield launching,the cutter head should be modified,and a number of advance cutting tools and shell tools should be installed on the cutter head; 3） During the cutting of the pile foundations directly by shield,the shield should advance slowly（ with less than 10 mm / min advance speed）,and the earth pressure,thrust and cutter head torque set should be stable; 4） During the cutting of the pile foundations directly by shield,lubricating and friction-reducing materials should be added into the excavation chamber so as to prevent the screw conveyor from being jammed by concrete blocks. After the shield passes the obstacle point,secondary grouting should be made to fill the annulus space behind the segment lining on basis of the monitoring results so as to control the settlement of the ground surface and the nearby buildings; 5） Cutting pile foundations directly by shield has advantages, including low cost,high safety and small environmental influence.