Thermal evolution and ventilation control strategies during construction and suspension periods in long-distance Subsea shield tunnels

This study utilizes on-site temperature monitoring data and a segmented coupled FDM-FEM numerical model to systematically investigate tunnel temperature distribution under the combined effects of external temperature, excavation length, and periods of work stoppage and resumption, with further optimization of ventilation parameters. The research results are as follows: (1) On-site monitoring shows that during tunnel boring machine operation, the tunnel environmental temperature from the tunnel face to the launching shaft exhibits a sharp drop followed by a gradual decrease, whereas after stoppage, it first rises and then falls. Beyond 3000 m behind the machine, temperature fluctuations remain within 0.5 °C. (2) The segmented coupling modeling method significantly improves simulation efficiency for long-distance tunnel temperature fields, producing results highly consistent with observed data. (3) The maximum tunnel temperature is positively correlated with external temperature and shows an exponential relationship with excavation length. (4) The average temperature in the shield working zone has a power-law dependence on ventilation rate, with cooling efficiency showing diminishing returns as airflow increases. (5) Required ventilation volume increases exponentially with rising external temperature, and the activation threshold for auxiliary cooling systems varies significantly under different temperature control standards. (6) Ventilation demand is linearly related to excavation length, with the critical excavation length decreasing significantly as temperature control standards become stricter. A coupled finite difference–finite element model was developed to efficiently simulate the thermal field in long-distance Subsea shield tunnels under varying external environmental temperatures, excavation lengths, and operational phases (construction/suspension). The approach enables determination of the ventilation rate required to maintain a target shield zone temperature.