富水砂卵石地层地铁盾构施工若干问题及对策

成都地铁工程大规模穿越市域富水砂卵石地层,该地层具有地下水位高、卵漂石含量高和卵石强度高等“三高”特点。一号线前期大量出现刀盘刀具磨耗严重、换刀频繁、带压换刀失效、刀盘结泥饼等现象,严重制约了盾构的掘进效率。在回顾成都地铁一号线一期工程前期盾构选型和施工的若干问题的基础上,提出并总结了富水砂卵石地层盾构选型和配置的一些具体对策,包括:树立“排出为主,破碎为辅”的地层处治理念,调整刀盘和螺旋出土器的结构型式、刀盘开口率、刀具布置型式,改进同步注浆浆液配比,优化泡沫系统和搅拌系统,改进碴土改良系统等。成都地铁一号线一期工程中后期以及二号线一期工程的施工实践表明:以上调整是有效的,盾构换刀距离和盾构施工平均月进度都获得了显著提高。

Problems and Countermeasures of Metro Shield Construction in Water-soaked Sand and Cobble Stratum

Chengdu Metro construction crosses water-soaked sand and cobble stratum in large scale. This stratum is characterized by three “highs”: high water table, high hard cobble content and high boulder content. In the early stage of Chengdu metro Line 1 construction, there was a large number of phenomena emerged such as serious wearing of the cutter heads and cutting tool, frequent replacing of the cutting tools, fail in replacing cutting tool with pressure, build-up of clay cake on cutter heads, which seriously restricted the shield tunneling process. On the basis of a review on problems of metro shield type selection and construction in the early stage of Chengdu Metro line 1 construction, this paper puts forward and summarizes some specific countermeasures on type selection and configuration of shield machine crossing water-soaked sand and cobble stratum. These countermeasures include building up the idea of “discharging primarily, breaking secondary”, adjusting the structural type of cutter heads and screw conveyor, and opening rates of cutter head and cutting tool layout, improving synchronized grouting slurry mixture ratio, optimizing foam system and mixing system, and improving soil system. As construction practice in middle and later periods of Chengdu metro line 1 and later Chengdu metro line 2 demonstrates that the above adjustments are effective, the distance of shield cutter replacing and average monthly schedule of shield construction gain remarkable improvement.