Experimental and Analytical Study on the External Water Pressure of a Composite Lining Considering the Waterproofing and Drainage System

Conventional analytical solutions for estimating the external water pressure neglect some factors associated with the waterproofing and drainage system (WDS), such as geotextile, circular drainage pipes, and waterproof membranes, which may lead to a gap between actual engineering observations and estimations. In this study, a reduced-scale model setup is designed to investigate the impact of the WDS on water pressure distributions. The model-test results indicate that the WDS dramatically reduces the water pressure on the secondary lining, while the effect on the initial lining is not apparent. An analytical solution is derived to analyze the external water pressure acting on the initial and secondary linings, and it is compared with model-test results. The results imply that the errors between the analytical solution and model test results ranged from -2.3% to 10.9%, thus verifying the proposed solution. Finally, a parametric analysis is conducted to reveal the WDS effect on water pressure. The following observations were made: (1) the external water pressure distribution acting on the initial and secondary linings is related to the distance between two adjacent circular drainage pipes, the surrounding rock mass and initial lining permeability, and the geotextile thickness. A small distance between the drainage pipes could increase water pressure reduction. (2) When the permeability coefficient of the surrounding rock mass is in the range of 1 x 10-8 to 5 x 10-6 m/s, the secondary lining water pressure prediction of the proposed solution is more than 54.1% lower than Liu's solution (Liu et al. 2013). The outcomes indicate the importance of the WDS effect on the water pressure under such conditions. This study results are helpful for the optimal design of composite lining structures and WDS. A model test is designed to investigate the waterproofing and drainage system (WDS) effect on water pressure. An analytical water pressure solution on the initial and secondary lining is derived and validated.The components of the waterproofing and drainage systems (waterproof membranes, geotextile, and blind pipes) are considered. The changes of the water pressure acting on the secondary lining are more significant than those on the initial lining, as the distance between two adjacent circular drainage pipes increases.