Physical modelling of a closed-loop steam-driven thawing technique for permafrost ground

This study investigated the performance of a steam-driven heating probe in warm saturated permafrost soils for pre-construction ground thawing and improvement. Steam-thawing model tests were conducted on frozen, saturated sand inside a permafrost simulator cell. The 290-mm-thick soil sample was first subjected to one-dimensional upward freezing, producing a temperature profile ranging from −1·5°C at the bottom to −0·5°C at the surface. Saturated steam at 105°C and 0·1 MPa was afterwards injected into a closed-end copper tube for about 3 h, followed by a 4-h recovery phase after steam heating ceased. Results showed that immediately on steam heating initiation, the thaw front rapidly propagated downward to the probe’s full depth and simultaneously expanded outward radially. The thawed zone continued expanding after heating ceased due to temperature-gradient-induced heat and moisture migration. As hydrothermal equilibrium was approached, the thawed zone cooled below 6°C yet remained unfrozen, allowing preloading and consolidation before refreezing for long-term stabilisation. In the closed-loop design, the phase change of pore ice consumed a significant portion of the energy released by steam injection, influencing system efficiency and design optimisation. Ongoing work focuses on post-thaw ground improvement and field-scale validation to advance infrastructure resilience in warm, ice-rich permafrost regions.