The performance of mechanical characteristics and failure mode for tunnel concrete lining structure in water-rich layer

Abstract

It's a challenging technical problem at home and abroad that it is inevitable to build tunnels in aquifer with the improvement and development of railway network, particularly under the current stringent environmentally-friendly prerequisite. Therefore, the conventional principle “drainage is dominant and combination of drainage and blockage” should be updated with “blockage is dominant and drainage is limited”. Under this background, the mechanical characteristics for tunnel lining structure in aquifer needs to be studied urgently. A series of model experiments were performed to investigate the load-bearing mechanism of the underwater tunnel lining under water pressure. To investigate the load-bearing characteristics of different types of linings, a fully closed water pressure exerting device for a non-circular section tunnel was invented. A large-scale model experiment (1:30) under combined water and soil pressures was conducted to investigate the mechanical characteristics, deformation, stress distribution, crack development process, and failure mode of the mined-tunnel lining in aquifer. The experiment results indicated that for mined-tunnel lining with large section the key sections for controlling instability of both the drainage lining and the waterproof lining were the bottom of the wall and the inverted arch under the two experiment conditions. One had only water pressure, and the other had a variable water pressure and constant soil pressure. For both types of lining structures, the bottom of the wall and the inverted arch appeared cracks and damaged in turn. Furthermore, based on unified strength theory, it was found that compression-shear failure on the inclined section will occur at the bottom of the wall under the action of water pressure, which was different from the compression bending failure at other parts. In this research, the reasonable ultimate water head of the waterproof lining (thick invert, or large invert) and the drainage lining for the high-speed railway tunnel of Class V surrounding rock with a design speed of 350 km/h was proposed which could provide reference for similar tunnel engineering.