Abstract: In cold regions, frostheaving phenomenon often occurs due to the phase change of pore water in the surrounding rock of a hydraulic tunnel under the influence of low temperature. First, a thermohydromechanical coupling model for Bulunkou hydropower station in Xinjiang is established using numerical simulation software based on the theory of elastoplastic mechanics and by considering the change in the thermodynamic parameters of the surrounding rock due to the low temperature waterice phase change. Subsequently, the elastoplastic frostheaving force solution of the surrounding rock, transient temperature field, frostheaving stress, and surroundingrock displacement are calculated. Finally, the change patterns in the frost depth and the stress and deformation before and after frost heaving are obtained through analysis. The results show the following. (1) The pore water of the surrounding rock undergoes a phase change under low temperature, and the freezingcircle moves to the interior of the surrounding rock over time. The freezing depth increases with time, and the maximum freezing depth is 2.04 m under 200 days of freezing. (2) The calculated stress of the surrounding rock is between 0.392 and 0.527 MPa, and the stress increases compared with that before the frost heaving. The horizontal displacement of the surrounding rock is -0.36 mm, and the vertical displacement varies from -9.59 to -8.41 mm. The states of the surrounding rock in terms of horizontal contraction and arch settlement are 0.36 and 1.18 mm, respectively.

Key words: cold region, tunnel engineering, waterice phase change, frost heavingcharacteristics, frostheaving force, numerical simulation