Study on energy conversion and intermittent temperature-control optimization of artificial ground freezing for connecting passages

Artificial ground freezing is characterized by high energy consumption and relatively low energy efficiency. Therefore, improving energy conversion efficiency is essential for achieving low-carbon, green construction. This study proposes an energy-conversion analysis framework that incorporates ice-water phase change and thermo-mechanical coupling, to rapidly calculate the energy utilization efficiency (EUE). A 3D thermo-mechanical coupled numerical model with nonlinearly varying temperature is developed based on field measurements. By comprehensively accounting for phase transition, key indicators—including the total energy output of the refrigeration plant, latent heat release of phase change, and elastic strain energy induced by frost heave—are quantified, thereby obtaining the evolving EUE curve. Using EUE as the governing metric, the entire freezing process is divided into four stages, and stage-specific energy-efficiency optimization strategies are proposed accordingly. The controlling effect of brine temperature on energy efficiency is further revealed, and an intermittent brine-temperature freezing mode is proposed. Finally, the coupled evolution of EUE and brine temperature is systematically analyzed, clarifying the magnitude of efficiency improvement under different intermittent operating conditions and the corresponding energy-saving mechanisms.