Soil effect on the bearing capacity of a double-lining structure under internal water pressure

Abstract

Water conveyance tunnels usually experience high internal water pressures and complex soil conditions. Therefore, shield tunnels with double-lining structure have been adopted because of their high bearing capacity. The effect of the interface between the segmental and inner linings on the bearing capacity has been widely investigated; however, the effect of soil on the internal water pressure bearing capacity has not been emphasized enough. Therefore, in this study, model tests and an analytical solution are presented to elucidate the effect of soil on the internal water pressure bearing capacity. First, model tests are conducted on double-lining models under sandy soil and highly weathered argillaceous siltstone conditions. The internal force and earth pressure under these different soil conditions are then compared to reveal the contribution of soil to the internal water pressure bearing capacity. Following this, an analytical solution, considering the soil—double-lining interaction, is proposed to further investigate the contribution of the soil. The analytical solution is verified with model tests. The analytical solution is in good agreement with the model test results and can be used to evaluate the mechanical behavior of the double-lining and soil contribution. The effect of soil on the bearing capacity is found to be related with the elastic modulus of the soil and the deformation state of the double-lining. Before the double-lining cracks, the sandy soil contributes 3.7% of the internal water pressure but the contribution of the soil rises to 10.4% when it is the highly weathered argillaceous siltstone. After the double-lining cracks, the soil plays an important role in bearing internal water pressure. The soil contributions of sandy soil and highly weathered argillaceous siltstones are 10.5% and 27.8%, respectively. The effect of soil should be considered in tunnel design with the internal water pressure.

摘要

目的

盾构隧道双层衬砌广泛应用于输水隧道，然而围岩的承载作用一直被忽略。本文通过模型试验揭示围岩-双层衬砌的共同承载特性，为高内水压输水隧道的围岩-双层衬砌共同承载设计方法提供支撑。

创新点

1. 揭示围岩条件对围岩-双层衬砌联合承载能力的影响规律；2. 建立围岩-双层衬砌联合承载理论解析方法。

方法

1. 通过模型实验，分析不同围岩条件下（砂性土、强风化泥质粉砂岩）双层衬砌内水压受力变形特性，并确定围岩和双层衬砌内水压承载比例以及围岩对双层衬砌承载能力的影响（图1和2）；2. 通过解析方法，揭示围岩承载比例随围岩弹性模量的变化规律（图22和23），并提出承载比例的内衬厚度优化设计方法。

结论

1. 内水压作用下，围岩承载能力与围岩弹性模量和衬砌变形状态有关；双层衬砌未开裂时，砂性土围岩承担3.7%的内水压，而围岩为强风化岩石时，其贡献上升至10.4%；双层衬砌开裂后，围岩在承受内水压方面起着更重要作用，即砂性土和强风化岩石的分担比分别为10.5%和27.8%。2. 隧道设计中应考虑围岩承载内水压能力的影响。