Study On The Freezing Damage Mechanism And Prevention Of Tunnels In Cold Regions

Relying on Zhu-Jiao-La mountain tunnel project in eastern Tibet cold area,temperature field of cold region tunnels, frost force were calculated and analyzed on the basis of the literature at home and abroad. The temperature field characteristics and its influencing factors have been simulated Analysis the coupling between temperature field and stress field in the cold area tunnel. The frost damage phenomenon and freezing mechanism of tunnels in cold regions were analyzed, at the same time the corresponding prevention and maintenance were proposed. The main results are as:①Temperature roughly show parabolic distribution in cold region tunnels, in cold season, the hole temperature is low, intermediate is high ; On the contrary, intermediate is low temperature, import and export is high temperature, in warm season. In the same tunnel section, the initial temperature of surrounding rock reach the highest, decrease along the border wall, under tunnel invert centre reach the minimum. Tunnel freezing range is the minimum in vault, the maximum under tunnel invert centre, the freezing range of surrounding rock in other position is between vault and invert centre.②In the tunnel entrance, surrounding rock temperature increases with the nonlinear addition of its depth. The frozen depth remarkably decreases with the rational addition of secondary concrete lining thickness and insulation layer thickness. The thermal conductivity changes of tunnel support structure concrete can only cause little influence to the surrounding rock frozen depth.③In considering the frost heave force, the surrounding plastic and the coupling effect of freezing and thawing, pressure and displacement of the tunnel has been changed, due to lining stiffness, the stress diversification of the tunnel lining structure is large. After setting the insulating layer, the tensile and compressive stress has decreased in cold regions tunnels, the displacement of all the surrounding rock has decreased, except inverted arch upward displacement.④Rock freezing and thawing is the basic factors of tunnel lining failure, and water migration enhances the frost heave destruction in the freezing process. According to the different frost heave mechanism and water of scales, the phenomenon of tunnel lining frost heave was divided into frost micro meson and macro three categories. Low temperature and the amount of water are two basic factors of frost damage in cold region tunnel. Improving impervious ability or setting insulation are effective measures for preventing tunnels frost damage in cold regions.