Numerical Analysis of Shield Tunnelling Breakthrough Working Shaft by Artificial Ground Freezing Method under Extreme Conditions Considering Phase Change Latent Heat

Abstract

The artificial ground freezing method has been widely used in shield tunneling breakthrough working shafts. The freezing effect was mainly considered in the previous research, and the heat generation of the shield machine was not considered, which has great influence in actual engineering. In this paper, a coupling calculation model, considering phase change latent heat, is establishes that by containing the freezing process and heat generation of the shield machine, the model is verified. A numerical simulation is carried out for several working conditions that may occur in actual projects, and the following conclusions are obtained. Although the heat dissipated by the normal tunneling of the shield machine will melt the frozen soil curtain that originally meets the design requirements, the thickness of the frozen soil curtain after melting cannot reach the initial design, though it is still within the safe range. In the process of a continuous rotation working condition, the bottom and sides of a cup-shaped frozen soil curtain are partially melted in the early 6 day stay of the shield machine, and the thickness is reduced to a relatively stable value of 0.8 m. In a temporary shutdown working condition, when the contact surface temperature between the shield machine shell and the frozen soil drops to −12 °C after almost 4 days of shutdown, the shield machine may not keep tunneling forward due to the freezing effect. The research results will benefit the freezing design and management of the shield tunneling breakthrough working shaft under extreme conditions.