Abstract: This paper presents a comprehensive study of the generation and distribution patterns of the temperature field within a large-diameter cup-shaped frozen soil wall used in shield construction of Nanjing Subway Line 10. Three dimensional finite element analyses are taken to elucidate various influential factors for the temperature field. It is found that, if the thicknesses of cup-shaped frozen soil walls can satisfy the designed amounts needed for the purpose of ground reinforcement, frozen wall forms in a clear sequence: firstly, in the outer tubes, then the intermediate tubes, and lastly, the inner tubes. The “closure time” of the frozen wall, which means the time period required for the full formation of the frozen soil wall, is heavily dependent on soil’s thermal conductivity as well as the original ground temperature. The closure time would decrease linearly with the increase of the thermal conductivity; it would increase linearly with the increase of original ground temperature of soil and volumetric heat capacity. For the concerned Nanjing shield tunneling site, it took around 12 days. This would have increased by approximate every one more day if the original ground temperature increases by every 5℃. The latent heat is found to be of no apparent influence in the cooling process of soil. Notwithstanding, the cooling speed varies much with different types of soil. Generally, the cooling speed of sandy cemented soil and sand is faster than that of clay cemented soil and clay respectively. However, they reach the phase-transitional-stage almost simultaneously. It is also noted that the frozen walls in sand are always formed 4 days earlier than those in clay regardless of whether the cement is in place or not. Results and conclusions from this research may play a useful role to aid designs of similar projects in the future.

Key words: large-diameter cup-shaped frozen soil wall, shield launching, temperature field, numerical simulation