高水压高渗透性地层泥水盾构开舱开挖面稳定机理研究

China will build a large of slurry shield tunnels underthe river and sea in next 10 years. The notable features of these tunnels are long distance tunneling,high permeable gravel strata, big buried depth, large -diameter sections.The cutting knives and cutterhead of slurry shield is hard to adapt to the long distance tunneling under so complex stratum, and it becomes a trend to be forced to open the pressure cabin of slurry shield to inspect and maintain the cutting knives and cutterhead. It is one of the key messures that the filtcake of cutting face of shield doesn't only transfer the slurry pressure, but also transfer the compressed air pressure to maintain the cutting face balance. In order to make clear the mechanisms that the filmcake chokes the air pressure and is penetrated by it, and that the slurry characteristics are demanded by the compact filmcake formation to strengthen the ability of choking pressure air, the test appliances of slurry leakage under high water pressure and high permeable strata,the test appliances of filmcake formation and air choking and air penetration have been made.Considering the characteristics of the supported pressure of air and mud under the condition of opening the pressure cabin, the stability model of cutting face of slurry tunnel is founded to analyze the condition of opening the pressure cabin.By means of the above model, the destroyed mode of cutting face under opening pressure cabin can been determined and the simplified method can been founded to calculate the supported air pressure. Finally, a set of core technologies available for opening pressure cabin can been founded for large-diameter section shield tunnel under high water pressure and high permeable strata.

未来10年，我国将大量修建越江海大型泥水盾构隧道，长距离施工、穿越高渗透性卵砾石、风化岩等复合地层、大埋深、大断面是其显著特点。目前，盾构刀具刀盘很难适应复杂地层中长距离掘进，在江底被迫停机带压开舱检查维护将成为了一种趋势。高水压高渗透地层如何形成致密、闭气能力强的泥膜，不仅能传递泥浆压力，也能传递气体支护压力是盾构开舱成败的关键。通过高水压高渗透地层条件下泥浆渗漏或劈裂试验、泥浆成膜-闭气-穿透试验和泥膜微细观结构试验，明确高渗透地层形成性质稳定、闭气能力强的泥膜对泥浆性质、颗粒级配要求，明确泥膜闭气-穿透模式及机理。结合盾构开舱气压和泥浆支护压力的特点，通过土-水-泥-气介质相互作用模型，建立盾构开舱开挖面稳定分析模型，明确开舱时开挖面失稳破坏模式及极限支护气压的确定方法。最终建立高水压高渗透性地层中泥水盾构带压开舱具有自主知识产权成套核心关键技术。

随着我国地铁建设、越江海隧道建设在全国主要城市逐渐推开，不得不面临长距离、高水压高渗透地层掘进环境，由于砂砾地层、卵石地层的石英含量较高，刀具和刀盘磨损严重，不得不在江底进行开舱修复刀具刀盘，如何在开挖面上形成致密稳定的泥膜是盾构开舱闭气保持开挖面稳定的成功关键。本项目针对砾砂地层、卵石地层开发了泥浆劈裂实验单元装置，并开展泥浆劈裂实验得到泥浆逸泥的两种模式-地层塑性劈裂破坏模式和地层渗透破坏模式及其发生条件；同时开展了高渗透地层中泥浆成膜-闭气实验，研究了泥膜的闭气值及闭气时间，认为泥膜的闭气值与泥膜中孔隙形态及毛细水吸力有关，泥膜的闭气时间与泥膜的形态有着密切关系，采取先采用较稀的纯膨润土泥浆渗透到地层10-100cm时泥浆堵塞地层孔隙，然后换成密度更高、粒径更大的泥浆（如纯膨润土+废弃泥浆的混合泥浆）再形成泥皮，最后形成的“渗透带+泥皮型泥膜”的闭气时间能够提高到60h以上，极大地提高了盾构开舱维修作业效率。项目还对泥膜的渗气系数进行测量，并计算了盾构开挖面维持压力所需要补充的气体量，确保盾构开舱时开挖面的安全稳定性。最后将本项目的研究成果应用于南京纬三路过江通道大断面泥水盾构开舱作业、深圳地铁盾构上软下硬地层中盾构开舱作业和厦门地铁3号线跨海盾构海底开舱作业，取得了圆满成功。