Research on the Mechanism of Frost Heaves Caused by Void Water Accumulation behind the Lining of High-Speed Railway Tunnels in Cold Regions

(1) Background: Lining voids and macroscopic water freezing are both prominent issues that threaten driving safety in high-speed railway tunnels. With the continuous expansion of the scale of high-speed rail tunnels in extremely cold areas in China, the issues of lining voids, water accumulation, and frost heaving have triggered heated discussions. The need to reveal the frost-heave mechanism is urgent. (2) Methods: Firstly, a simulation experiment of the frost heaving of accumulated water was carried out based on the discharge conditions of accumulated water. Secondly, a numerical model was used to study the evolution process of frost heaves caused by accumulated water in voids. Finally, a drainage coefficient was introduced to propose a method for calculating the frost-heave force of accumulated water in voids. (3) Results: The blockage of the drainage channel leads to the generation of frost-heave force; the freezing/thawing process of the void water develops from the thinnest part to the thickest part of the void edge, and the freeze/thaw cycle of the water body causes the frost-heave force to become greater and greater in the evacuated cavity. The higher the height and the closer the drainage channel is to the hollow bottom, the greater the frost-heave force when the accumulated water freezes. (4) Conclusions: When the evacuated water freezes, it develops from the thinner edge to the thicker center. The magnitude of the frost-heave force is affected by the freeze/thaw cycle, the height of the evacuated cavity, and the position of the drainage channel.