Geothermal heat pump solutions for frost heave control in railway subgrades

Abstract

Frost heaving in railway subgrades presents persistent challenges for rail operations in cold regions, causing significant track deformation and maintenance demands. This study introduces and evaluates a distributed heating system driven by geothermal heat pumps (GHP-DH system) to sustainably mitigate frost heaving in a 20-meter-long section of a heavy-haul railway during seasonal freeze-thaw cycles. Field measurements were conducted to analyze key parameters, including the temperatures of the GHP-DH heat exchangers, subgrade soil temperature fields (T_S), the depth of the freezing front (d_FF), and track deformation due to frost heaving (D_T). The results demonstrated that the GHP-DH system maintained a stable heat supply above 50 °C, effectively reducing the frozen domain and extreme T_S fluctuations within the subgrade. The system reduced the maximum d_FF from 197 cm to 88 cm, ensuring the freezing front remained above the shallowest depth for groundwater migration through capillary action. Additionally, inclining the heat-supply pipes at a 3° angle minimized the transverse d_FF difference from 49 cm (unheated section) to 13 cm, significantly reducing horizontal track irregularities. Spacing the heat-supply pipes at 2.5 m further limited longitudinal d_FF differences to within 20 cm, preventing shortwave vertical track irregularities. In the unheated section, maximum D_T exceeded 9.4 mm, whereas the heated section maintained D_T fluctuations between –3 mm and +3 mm, well within the specified maintenance standards. These findings confirm that the GHP-DH system is a highly effective and sustainable solution for frost heave mitigation in railway subgrades, offering significant potential for improving track stability and reducing maintenance demands in cold climates.