大直径泥水盾构砂地层开挖面被动破坏模型试验及机理分析

Large-diameter size slurry shield tunneling method has been widely used in the construction of underwater tunnels in complicated condition in China. As the large section of slurry shield tunnels, the slurry pressure gradient in pressure chamber cannot keep match with the soil and water pressure in the sand. The support slurry pressure on the crown of the excavation face is larger than the soil and water pressure, which makes the soil face a grim problem of passive failure. This research carries out base on the problem by model test and mechanism analysis. Through the slurry penetration test, the transform role for slurry pressure as slurries breaking through the filter cake and fracturing in sand is explored. And the effect of slurry infiltration on the tunnel face stability is discussed. In the centrifuge model, a rigid plate with holes in it and latex film pasted outside it is used to simulate the tunnel face, and three model tests are conducted with different cover over diameter (C/D) ratios. The transformation and passive failure modes of soils are investigated in sand. And the passive failure mechanisms of tunnel face for large-diameter size slurry shield in sand is revealed. This research results enrich and perfect the theory of excavation face stability control for shield tunnel, and has an important guiding significance for controlling the excavation face stability for large-diameter size shield tunnel.

大直径泥水盾构技术在大断面、强透水等复杂条件的水下隧道建设中应用越来越多。由于隧道断面大，压力舱泥浆压力梯度很难与地层土水压力梯度较好地保持一致，开挖面顶部承受的支护泥浆压力显著大于地层土水压力，致使开挖面面临较严峻的被动破坏问题。本项目针对大直径泥水盾构砂地层开挖面被动破坏问题，通过砂地层泥浆渗透试验，探索了砂地层中泥浆冲破泥膜、发生劈裂破坏的过程中泥浆压力在地层中的传递规律，明确泥浆渗透作用对开挖面稳定性的影响；并在离心模型试验中改进了以往研究中模型盾构的刚性开挖面，以带孔刚性板外包乳胶膜代替开挖面，明确了开挖面土体变形规律和破坏模式，揭示了大直径泥水盾构砂地层开挖面被动破坏失稳机理。研究成果不仅丰富和完善盾构隧道开挖面稳定控制理论，也对大直径盾构隧道开挖面稳定性控制也有重要的指导意义。

针对大直径泥水盾构砂地层开挖面被动破坏问题，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压力在地层中的传递规律、泥膜的破坏模式及影响因素，并通过离心模型试验和数值模拟方法，研究不同C/D条件下砂地层开挖面被动失稳过程中土体变形规律和破坏模式。结果表明，孔隙比是影响泥膜闭气性的关键因素；压气条件下泥膜出现干裂破坏、小孔破坏和多孔破坏等破坏形态；相比于无反压条件，设置反压条件下形成的泥膜结构更为疏松，反向水压力抵消了部分泥浆压力，降低了泥浆压力的转化率；滤水量/泥膜体积可作为评价泥膜致密程度的指标。随着C/D从0.8增大到1.5，开挖面前方土体变形范围逐渐增大，标准化开挖面被动破坏支护力从23增加到47，其破坏模式逐渐从倒梯形趋向于烟囱型。研究成果不仅丰富和完善盾构隧道开挖面稳定控制理论，也对大直径盾构隧道开挖面稳定性控制也有重要的指导意义。