The effect of external water pressure on the liner behavior of large cross-section tunnels

Recent extreme weather with heavy rainfall has brought new challenges to the operation of a karst tunnel as a large amount of groundwater flowing toward the tunnel in a short time exceeded the drainage capacity and caused high external water pressure. By evacuating the air in the inner space of the tunnel structure, an apparatus was developed to simulate the external water pressure on the tunnel structure. It was also employed to study the behavior of a highway tunnel structure with a large cross section considering cavities behind the liner. The results showed that the bending moment of the liner increased with the external water pressure, which helps to decrease the nonuniform distribution of the thrust force, and the maximum bending moment and eccentricity were generally located at the knees or side walls. Lower external water pressure contributed to reducing the eccentricity of the liner while higher external water pressure does not further reduce the eccentricity. Under external water pressure, fractures appeared first at the knee, then at the invert and finally at the vault. The air tightness tests under external water pressure also showed that the cavity decreased the bearing capacity of the liner and significantly aggravated the fractures in the liner nearby. The results help to estimate the bearing capacity of the liner under external water pressure, and the method of simulating external water pressure can also be used to study tunnels with different cross section geometries. (C) 2016 Published by Elsevier Ltd.