The artificial freezing construction technology, compared to other methods, offers several advantages, including superior waterproofing capabilities and the absence of environmental pollution. This technique is particularly prevalent in the construction of tunnels in challenging environments, where the dynamics of the freezing temperature field during the freezing process have consistently been a key area of interest during actual construction activities. In the Sanya Estuary Channel Submarine Tunnel Project, a three-dimensional transient model was developed using COMSOL finite element software to deeply analyze the formation and temperature distribution of the permafrost curtain. Two alternative schemes were designed to improve the original design by optimizing the layout of the permafrost pipeline. Comparative analysis shows that the isotherm −10 °C intersected at 14 days in the original scheme, 23 days in Optimized Scheme 1, and 24 days in Optimized Scheme 2, indicating a 10-day delay in Scheme 2 versus the original, yet still meeting the 25-day deadline. After 40 days of active freezing, the greatest difference in permafrost curtain thickness was observed at the east wall (downstream), with Scheme 2 differing by 1.05 m from the original and by 0.23 m from Scheme 1. Scheme 2 achieved an average permafrost curtain thickness of 4.18 m around the tunnel, exceeding the 3.5-m design requirement. The mean temperatures in the strong and weak freezing zones of Scheme 2 were below −10 °C and −8 °C, respectively, aligning with design standards. Given the conservative nature of the initial plan, Optimized Scheme 2 is highly practical for implementation and offers significant cost savings.

Using COMSOL finite element software, a three-dimensional numerical transient model of an underground tunnel collapse vertical freezing repair project was established. The model was altered to change the head difference, allowing for analysis of the development of the permafrost curtain, the time of intersection circles, and the freezing temperature field cloud diagram. The results indicated that, without seepage, development of the upstream and downstream permafrost curtains was stable and uniform. However, under seepage conditions, development of the upstream and downstream permafrost curtains became increasingly uneven with increasing seepage velocity. The downstream side of the soil body began freezing earlier than the upstream side, and the final temperature was lower. The intersection time of the freezing wall was an important indicator of development of the permafrost curtain, and the freezing time of the freezing wall was the most critical indicator. A hydraulic head difference of 1 m was found to significantly impact the development of the freezing wall, with less influence from seepage velocity on the overall permafrost curtain intersection time. However, the intersection time of the isotherm increased significantly with increasing seepage flow rate. The findings from this project provide a theoretical reference for future restoration design.