基于泥浆过滤-渗透的泥水盾构砂地层泥膜形成及破坏机理研究

With the increasing of cover depth in submerged slurry shield tunnels, the hydrogeological conditions become more and more complex, the challenges of filter cakes formation and excavation faces stability in difficult conditions have become the important problems for shield tunneling in china. In this project, the infiltration law as slurries infiltrate into sand is revealed from the perspective of the relationship between the particle size of slurries and pore size of soils and the characteristics of the mud fluid, and the permeation-osmosis model of slurries is established. The effect of pressure differences and ultra-high pressure (up to 2MPa) as setting pressure against the infiltration on the properties of filter cakes is discussed. The function of filter cakes during the long time stop and opening the excavation chamber under air pressure of slurry shield TBMs is simulated. And the failure mechanisms of filter cakes in difficult conditions are present. Finally, the evaluation indexes and its range of filter cakes are determined by test studies and the typical slurry shield projects, the quality evaluation method of filter cakes is formed. Thus, this application has an important role in guiding slurries preparation, filter cakes failure mechanisms and quality evaluation during submerged slurry shield tunnels construction, and it is very urgent and necessary in China.

随着水下泥水盾构工程隧道埋深不断增大，水文地质条件越来越复杂，不断突出的泥浆成膜及复杂工况下开挖面稳定的问题，成为困扰我国盾构施工的重要难题。本项目拟从泥浆颗粒粒径与地层孔径间的关系和泥浆流体特性的角度，揭示泥浆在地层中的渗透规律，建立泥浆在地层中的过滤-渗透模型。通过设置反压研究不同压差及超高水压（最高达2MPa）等压力条件下对泥膜性质的影响，模拟盾构长时间停机及带压开舱等工况下开挖面泥膜的作用机制，从受力和微观结构两个方面揭示泥膜的破坏机理。最后结合典型的泥水盾构工程确定泥膜的评价指标及范围，形成泥膜的质量评价方法。本项目对于我国大型水下盾构隧道建设中泥浆配制、泥膜破坏及质量评价问题具有重要的指导作用，并显得非常必要和迫切。

本项目针对泥水盾构砂地层泥浆成膜及复杂工况下开挖面稳定的问题，通过砂地层泥浆渗透及泥膜破坏试验，探索砂地层中泥浆成膜过程中泥浆渗透规律、不同压力条件下泥膜的形成和破坏模式、泥膜质量评价方法。结果表明，颗粒级配是影响泥浆在砂地层中过滤-渗透行为的主要因素，泥浆在砂地层中的过滤-渗透行为降低了地层渗透性；泥浆在砂地层中的渗透本质上属于存在起始水力梯度的非达西渗透，泥浆流体性质是其在砂地层中渗透时存在起始水力梯度的主要原因；渗透压差越大，形成的泥膜越致密，反向水压的存在导致泥膜内部孔隙整体变大；泥膜在闭气过程中可能出现：干裂破坏、小孔破坏、多孔破坏三种模式；Q/V、泥浆压力转化率和泥膜渗透系数是评价泥膜质量的重要指标。研究成果对推动我国大直径水下隧道建设、保障开挖面稳定有重要的意义。