Field evaluation of a ground-source heat pump system for frost heave control in high-speed railway subgrades

Frost heave in seasonally frozen subgrades destabilizes railway track geometry and leads to significant maintenance demand in cold regions. As a thermally driven process, its mitigation requires reliable and energy-efficient temperature control. This study develops and field-tests an integrated ground-source heat pump (GSHP) thermal management system designed to actively heat frost-susceptible subgrade zones using shallow geothermal energy. The system consists of vertical heat-collector pipes, horizontal heat-supply pipes, and modular surface heat-pump units. A 20 m full-scale test section was implemented on the Shenyang–Baishan high-speed railway and operated throughout the 2024–2025 winter. Pre-installation heat-load modeling identified a peak thermal demand of 1183 W/m, guiding the deployment of ten 1.2 kW heat-pump units with intermittent operation (2.5 h ON/0.5 h OFF). During operation, outlet pipe temperatures remained stable at 18.7 °C, reducing frost depth to 70–83 cm at the track center and 34–44 cm at the shoulder, and suppressing track heave to within 5 mm. In contrast, untreated subgrade experienced frost penetration of 195–224 cm and heave up to 6.6 mm. These results demonstrate that GSHP-based active heating can effectively limit frost penetration, elevate minimum soil temperatures, and enhance the service reliability of transport infrastructure. The findings also highlight the potential for geothermal-based thermal management in energy-intensive cold-region applications.