Research On Mechanical Properties Of Highway Tunnel Second Lining With Large Cross-Section In Water-Charged Strata

In recent years, with the development of the highway system and the increasing of traffic volume in our country, an increasing number of large cross-section highway tunnels with three lanes and even more lanes will be constructed. In the southwest areas of China, long tunnels usually pass through water-charged karst strata in the high rainfall areas. Once the drainage system failed, the tunnel structure will endure certain water pressure in the case of heavy rains. The voids behind the tunnel structure will make the internal force of the second lining more complicated and endanger the security of structure. Therefore, the research on mechanical properties of highway tunnel second lining with large cross-section in water-charged strata need be conducted urgently.Supported by the Chongqing Shuangbei Tunnel Enginnering, the field testing of internal force, scaled model test and numerial modelling were conducted to study the mechanical properties and failure mode of large cross-section highway tunnel. Below are the main research content and results:1) By installing test instrument in the typical sections located in the surounding rock which are classified as Grade â…¢, â…£ and â…¤, the internal force and safety factor were calculated and analysed using the data obtained from field testing. Besides, the most fragile parts of the tunnel structure were determined on the basis of testing result and real damage of the practical enginnering.2) Considering effects of the different water pressure and the location of the void, the scaled model test was carried out to study the internal force and damage of secod lining with large cross-section. The surrounding rock pressure and water pressure acting on the tunnel structue were simulated using the surrounding rock pressure loading device and uniform water pressure loading device respectively. And the suggested critical water pressure before the appearance of cracks was obtained finally.3) Based on the fluid-mechanical interaction principia, fifteen numerical models were built using finite difference software FLAC3D. Given that the drainage system has failed, the water pressure behind the second lining, the bending moment, axial force and safety factor of tunnel structure were calculated and analysed under the action of different water pressure (0/10m/20m/30m). The effects of void location and void size on the tunnel structure were analysed as well.