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

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.