Applicability evaluation of thermal insulation for existing ballasted railway and its strengthening method in cold regions

Abstract

Insulation boards are widely adopted to mitigate frost heave in cold-region subgrades. However, their effectiveness and applicability under shallow groundwater levels and high water contents remain insufficiently understood. In this study, a coupled moisture–heat–mechanical model incorporating groundwater effects and active heating was developed and validated by field monitoring data. Using the validated model, the frost heave mitigation performance of insulated subgrades was systematically evaluated under varying groundwater levels, water contents, and subgrade heights. The results show that insulation boards reduce freezing depth and frost heave by enhancing the thermal resistance of the shoulder region. The maximum freezing depth at the shoulder decreased by more than 30%, while lateral differential frost heave was reduced by up to 44%. However, under shallow groundwater levels, high water content, and low subgrade heights, adverse frost heave deformation still exceeded 15 mm. For such unfavorable scenarios, a combined insulation–heating strategy was proposed, which reduced the freezing depth at the shoulder by more than 80% and substantially improved subgrade thermal stability. Based on the simulation results, a minimum heating temperature of 20 °C is recommended. These findings provide a scientific basis and engineering guidance for the integrated mitigation of frost-related distress in existing railway subgrades in cold regions.