Research on Frost Heaving Characteristics of Hydraulic Tunnels' Wall Rock in Cold Regions Based on Phase Transition and Water-Heat-Stress Coupling

In order to study the problem of frost damage to wall rock caused by hydraulic tunnels' phase transition between water and ice at low temperatures in cold regions, a three-field coupling governing equation considering temperature, seepage and stress was deduced. Taking a water conveyance tunnel in Xinjiang as the research object, a three-dimensional frost heaving finite element model was established based on the deduced coupling equations using finite element software. By numerically simulating the process of frost heaving, the spatial distribution and variation law of the frozen area and frost heaving force were obtained. The present study showed that the frozen area of wall rock at the tunnel entrance is spatially distributed in a long-necked funnel shape, and the frost depth of the section gradually decreases along the depth of the tunnel. Due to the hysteresis of heat conduction, the peak point of the maximum freezing depth of wall rock appears after the minimum ambient temperature. The circumferential distribution law of frost heaving force in wall rock remains consistent with the depth, that is, the maximum frost heaving tension occurs at the arch top and arch bottom and decreases to zero in the circumferential direction, and then it turns into the frost heaving pressure which gradually increases to the maximum at the arch waist. Along the depth, at 20 m away from the tunnel entrance, the frost heaving force at the arch top, arch waist and arch bottom is divided into a steep decline zone and a slow decline zone. After being frozen for 30 to 150 days, the growth rate of the absolute value of the maximum frost heaving force at the arch top and arch bottom is about 1.5 times that of the arch waist. The frost heaving force has greater influence on the arch top and arch bottom than on the arch waist.

Automated summary

In this study, a three-field coupling governing equation considering temperature, seepage and stress was deduced to investigate the problem of frost damage to wall rock caused by the phase transition between water and ice in hydraulic tunnels in cold regions. A three-dimensional frost heaving finite element model was established based on the deduced coupling equations using finite element software. By numerically simulating the process of frost heaving, the spatial distribution and variation law of the frozen area and frost heaving force were obtained. The results showed that the frozen area of wall rock at the tunnel entrance has a funnel shape and the frost depth gradually decreases along the depth of the tunnel. The frost heaving force has a consistent circumferential distribution law with depth, with the maximum frost heaving tension occurring at the arch top and arch bottom and turning into frost heaving pressure at the arch waist. The frost heaving force has a greater influence on the arch top and arch bottom than on the arch waist.