Experimental study on heat transfer and thermal storage performance of tunnel GHEs in cold regions

Frost damage at tunnel entrances in severely cold regions presents a major threat to tunnel safety and operational reliability. To address this challenge, this study investigates the use of tunnel lining ground heat exchangers (GHEs) for active frost prevention. A test platform for ground heat exchangers was established in laboratory, enabling a systematic analysis of GHE heat transfer performance and surrounding rock heat retention under varying operational and environmental conditions, including inlet temperature, flow velocity, pipe arrangement, ambient temperature, and ventilation speed. Results indicate that raising the inlet temperature and flow velocity improves the heat exchange rate, although the improvement effect weakens at higher levels due to nonlinear behavior. A pipeline configuration aligned with the tunnel axis increases the heat exchange rate by about 7.7 %. A 5 °C decrease in ambient temperature results in roughly a 10 % increase in heat loss and a 10 % decline in thermal retention, especially pronounced in the −8 °C to −18 °C range. Ventilation velocity has a pronounced impact; increasing it from 0 m/s to 1 m/s significantly alters both heat loss and thermal retention. The system shows greater sensitivity to ventilation variation under conditions of low inlet temperature and high flow rate. These findings offer guidance for the engineering application and optimization of GHE systems in tunnels situated in cold climates.