Analysis of temperature field evolution in ground freezing construction of twin tunnels in a coastal urban area.

In the field of underground engineering, the artificial ground freezing method has emerged as a highly effective technique due to its excellent impermeability, controllability, and minimal environmental impact. This method is particularly advantageous in complex geological and urban settings, making it widely used in tunnel construction under challenging conditions. However, in the case of twin-tunnel (or two-lane tunnel) projects, accurately predicting the temperature field during the freezing process remains a critical challenge. One of the key issues lies in the uncertainty of excavation rates, which significantly affects the development and control of the frozen wall. This paper establishes a three-dimensional water-heat coupling model based on the actual project of an underground two-lane tunnel in a city near the sea. Through numerical simulations, the model analyzes and investigates the temperature field maps, effective permafrost curtain thickness, and the cooling law of the two primary surface paths. The findings indicate that the development of effective permafrost curtain thickness is significantly influenced by seepage. The upstream side of the left tunnel experiences the greatest impact at 45°, 90°, and 135°, with the downstream side of the right tunnel showing less influence in five directions. The development trend of effective permafrost curtain thickness in the 90° direction of the left tunnel is opposite to that of the right tunnel, with a difference of 1.7393 m, both reaching the design standard thickness. Over time, the freezing tubes continue to produce cold, causing the temperatures in the freezing zones to decrease. The temperature of the main face 1 exhibits a 'double W' shape distribution in the temporal-spatial change, while the temperature of the main face 2 shows a 'W' shape distribution in the same context.