Canadian Geotechnical Journal, Ahead of Print.
Foam conditioning is a widely adopted technique in earth pressure balance (EPB) shield tunneling for the purpose of reducing sand permeability and preventing water spewing. The permeability of foam-conditioned sands differs from that of natural sands due to the presence of foam bubbles. This study investigated the effect of water pressure on the permeability of foam-conditioned sands using novel laboratory permeability tests. The water pressure, for the first time, is decoupled with the hydraulic gradient, owing to a newly developed permeameter with the controllable downstream hydraulic pressure in the laboratory. The results show that the permeability is significantly affected by the water pressure, and the effect is also predominantly dependent upon the foam injection ratio. The initial hydraulic conductivity increases with the increasing water pressure, while the initial stable period duration decreases. The water-plugging structure formed by foam bubbles and sand particles is prone to be damaged under high water pressure due to the shrinkage of foam bubbles. This means that the existing permeability tests with low water pressure underestimate the permeability of foam-conditioned sands. The underlying mechanism of water pressure in modifying the permeability of foam-conditioned sands is also examined from a particle-scale perspective.

中文翻译：

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土压平衡盾构施工中水压对泡沫砂渗透性的影响

加拿大岩土工程杂志，印刷前。
泡沫调节是土压平衡 (EPB) 盾构施工中广泛采用的技术，目的是降低砂土渗透性并防止喷水。由于泡沫气泡的存在，泡沫调节砂的渗透性与天然砂的渗透性不同。本研究通过新颖的实验室渗透性测试研究了水压对泡沫调节砂渗透性的影响。由于实验室新开发的具有可控下游水压的渗透计，水压首次与水力梯度解耦。结果表明，渗透率受水压的影响显着，而且这种影响也主要取决于泡沫注入比率。初始导水率随着水压的增大而增大，而初始稳定期持续时间减小。泡沫气泡与砂粒形成的堵水结构在高水压下容易因泡沫气泡的收缩而被破坏。这意味着现有的低水压渗透性测试低估了泡沫调理砂的渗透性。水压改变泡沫调节砂渗透性的基本机制也从颗粒尺度的角度进行了研究。