Numerical calculation of temperature field of freeze-sealing pipe roof method in Gongbei tunnel

This paper took the Gongbei tunnel in the Zhuhai Connection Section of the Hong Kong-Zhuhai-Macao Bridge as an example to study the development of the temperature field of the Freeze-Sealing Pipe Roof Method. Based on the heat transfer theory of two-dimensional porous media, the FEM software COMSOL was used to numerically analyze the actual working conditions of the active freezing period, the numerical calculation was verified by field measurement. The development and distribution of the temperature field before and after the opening of the special-shaped freezing pipes was studied. The results showed that: when freezing for 30 days, the concrete pipe was completely wrapped by frozen soil, and a continuous frozen soil curtain began to form between the concrete pipe and empty pipe, when freezing for 50 days, the empty pipe was completely wrapped by frozen soil, when freezing for 90 days, the thickness of the frozen soil curtain at the concrete pipe and the empty jacking pipe reached 2.0 m, which met the design requirements. The average temperature change rates of the temperature measurement point at the midpoint between the concrete pipe and empty pipe were -0.86 ℃/d, -0.88 ℃/d and -0.25 ℃/d before the opening of the special-shaped freezing pipes, within 10 days after opening and within 10-20 days after opening, respectively. After that, the temperature of each measuring point tended to be stable, thus forming a relatively uniform frozen soil curtain. The results could provide technical reference for similar projects in the future.