• Geothermal heat pump system effectively proposed to mitigate railway subgrade frost heave. • Vertical heat diffusion stronger than longitudinal, soil temperature rise up to 8.85 °C at 20 cm. • Effective thermal influence radius prediction links freezing depth and heating duration. To address frost heaving of railway subgrade in cold regions, in this study, we propose a geothermal heat pump (GHP)-based heating system and a corresponding distribution scheme to actively supply artificial heat to thaw subgrade. A full-scale half subgrade test platform for a class I single-track railway is designed, and the subgrade temperature field is monitored and analyzed. The effective thermal influence radius of the heating system is defined as the longitudinal extent that controls the freezing depth of the subgrade to below the critical value in a certain period of time, and a method for predicting the effective thermal influence radius is presented. The results show the following. The heating temperature of the heat pump system can exceed 30 °C, and the coefficient of performance ( COP ) can reach 6.9. After heating for two days, the temperatures of the soil mass at vertical distances of 20 cm, 40 cm, and 60 cm away from the heat-supply pipe rise by 8.85 °C, 1.68 °C, and 0.80 °C, respectively. The temperature increase rate of the subgrade is higher in the vertical direction than in the longitudinal direction. The effective thermal influence radius is proportional to the heating time and the detrimental freezing depth. With detrimental freezing depths of 30 cm, 35 cm, and 40 cm, the effective thermal influence radii after heating for five days are 0.44 m, 0.64 m, and 0.83 m, respectively; to have a thermal influence radius of 1.5 m, the required heating times are 53 days, 41 days, and 35 days, respectively. In practice, the longitudinal spacing between heating systems along the line should be reasonably designed according to the detrimental freezing depth of the subgrade and the requirement for frost heaving treatment time to ensure the thawing ranges of adjacent heating systems are continuous within the specified period of time
Hu et al. (Fri,) studied this question.