Abstract: In the process of shield tunneling in saturated sand layer, improper support of excavation face may cause collapse or extrusion failure of excavation face. In order to ensure the stability of the excavation face, pressure mud was usually used to balance the earth pressure and water pressure on the excavation face. Because the mud pressure in the pressure chamber was greater than the hydrostatic pressure in the formation, the mud would infiltrate into the formation around the excavation face. In this case, part of the effective support force was transformed into excess pore water pressure, which caused the decrease of the effective support pressure on the excavation face, thus the stability of the excavation face was reduced. Therefore, the influence of slurry infiltration and excess pore water pressure must be considered in the design of support pressure. Furthermore, the stability of excavation face would also be affected by stratification. Combined with the calculation model of excess pore water pressure caused by shield tunneling in saturated sand layer and the results of indoor slurry infiltration test, the influence of slurry infiltration and excess pore water pressure on the stability of excavation face was analyzed, and the influence of stratum stratification and hydraulic gradient on micro stability of excavation face was discussed. The research results show that in the design of support pressure, additional pressure must be added to make up for the loss of effective support pressure in the process of mud infiltration. By comparing the hydraulic gradient on the excavation surface in homogeneous confined aquifer and semi-confined confined aquifer, it is found that the excavation face of shield tunnel in semi-closed confined aquifer is more stable than that in homogeneous confined aquifer. Without slurry support, the hydraulic gradient on the excavation face is difficult to maintain the stability of the soil particles on the excavation face. Therefore, it is suggested that the pressure slurry should be used for the support of the excavation face of shield tunnel in saturated sand layer.

Key words: tunnel engineering, shield tunnel, saturated sand layer, stability of excavation face, slurry infiltration, excess pore water pressure

摘要： 饱和砂层盾构隧道掘进过程中，不当的开挖面支护可能导致开挖面坍塌或挤出破坏。为保证开挖面稳定，压力泥浆通常用来平衡开挖面上的土压力和水压力。因为压力仓中的泥浆压力大于地层中的静水压力，泥浆会向开挖面周围地层入渗。在这种情况下，部分有效支护力转化为超孔隙水压力，导致开挖面上的有效支护压力减小，从而降低开挖面的稳定性。因此，设计支护压力时必须考虑泥浆入渗作用和超孔隙水压力的影响。另外，地层成层情况也会影响开挖面稳定性。结合饱和砂层盾构掘进引起的超孔隙水压力计算模型和室内泥浆入渗试验结果，分析泥浆入渗和超孔隙水压力对开挖面稳定的影响，并讨论地层的分层情况和开挖面水力梯度对开挖面微观稳定的影响。研究结果表明：在设计支护压力必须附加额外压力以弥补泥浆入渗过程中有效支护压力的损失；通过对比均质承压水层和半封闭承压含水层中开挖面上的水力梯度发现，相较均质承压含水层而言，盾构隧道在半封闭承压含水层中掘进时开挖面更加稳定；在没有泥浆支护的情况下，开挖面上的水力梯度很难维持开挖面上土颗粒的稳定，因此建议压力泥浆用于饱和砂层盾构隧道开挖面支护。

关键词: 隧道工程, 盾构隧道, 饱和砂层, 开挖面稳定, 泥浆入渗, 超孔隙水压力