Finite-Element Analysis of Heat Transfer of Horizontal Ground-Freezing Method in Shield-Driven Tunneling

Abstract

When applying the artificial ground-freezing method in a shield-driven tunnel, the design of the freezing zone and freezing time is of practical interest. Therefore, the distribution and evolution of heat transfer in a frozen soil wall are key issues in the examination of the freezing effect. In this study, the horizontal ground-freezing method for soil reinforcement in shield-driven tunneling was considered. A cup-shaped freezing scheme was adopted at the launching shaft of the shield-driven tunnel. Three-dimensional (3D) finite-element analysis was used to examine the heat transfer within the cup-shaped frozen soil wall. By this method, the feasibility of the artificial ground-freezing method in the shield tunneling of Nanjing Subway Line 10 was demonstrated. Four types of soil were considered as the in situ soils surrounding the shield machine: sandy, cement-admixed sandy, soft clay, and cement-admixed soft clay. The simulation results indicate that the cement-admixed sandy soil was the most favorable material in terms of ground freezing; it had the highest decreasing rate of temperature in the process of ground freezing. In contrast, the soft clay was the most unfavorable material in terms of ground freezing. The results imply that the closure time of the cup-shaped frozen soil wall was sensitive to the thermal physical properties of soils in addition to the in situ water content.