Development and Numerical Modelling of a Novel Tunnel Freezing Segment for Tunnel Construction

In shield tunnel construction, it is critical to stabilize water‐bearing strata and prevent leakage in the portal zone when the shield machine arrives at the receiving shaft. Conventionally, cement‐based reinforcement and artificial ground freezing (AGF) methods are employed to strengthen the portal zone and prevent seepage. However, challenges remain, as seepage can occur along the excavation gap between tunnel linings and the surrounding soil due to unreliable synchronous grouting or shield deviation. To address this issue, this study proposes a novel built‐in freezing tunnel segment (FTS) system, in which freezing tubes are integrated into precast shield segments. The FTS enables adaptive and precise freezing of both the excavation gap grout and surrounding soil, forming a supplemental frozen wall to block groundwater leakage. Multi‐method validation was conducted and the results show that the FTS‐enhanced AGF system eliminates seepage risks in high‐permeability strata: (1) In‐situ experiments confirmed the FTS's freezing efficiency (reaching −14.3°C at 80 mm distance within 48 h); (2) Field implementation in Tianjin Metro Line 10 demonstrated effective seepage control, freezing the excavation gap below −13°C; and (3) A numerical thermo‐mechanical numerical model, calibrated against experimental data and incorporating latent heat effects, accurately replicated ground thermal responses. This integrated approach provides an alternative to conventional AGF systems that employ external freezing tubes and enables precise ground freezing under challenging hydrogeological conditions.