A new ground freezing method using freezing tunnel segment for tunneling construction: A case study in Tianjin, China

The reception of tunneling shields is a critical stage in shield tunnel construction, during which the portal of the receiving shaft is broken, and the shield machine enters the shaft. In this process, groundwater and soil may gush into the receiving shaft and cause engineering accident. Conventional shield arrival technologies such as soil reinforcement and often struggle to effectively seal seepage pathways within the excavation gaps at the portal zone. This paper proposes a new ground-freezing method adopting an innovative ‘Freezing Tunnel Segment’ (FTS) aiming at effectively mitigating ground water leakage in the tunnel portal. The FTS is a new type of tunnel segment with built-in freezing tubes that can flexibly and precisely freeze the surrounding soil. This allows the formation of a frozen wall within the excavation gap and enhances the seepage plugging, effectively blocking groundwater inflow into the tunnel portal. In this study, the designment of the FTS is introduced in detail and a freezing experiment on a single FTS block is presented. Furthermore, the engineering case study using FTS enhanced ground freezing system for tunnel reception in Tianjin, China is investigated. The freezing experiment indicates that the frozen wall generated by FTS extended radially at a rate of about 6 mm/h. On-site monitoring from the practical engineering shows that the frozen wall reached a temperature of −12 °C with a thickness of 150 mm and achieved closure within 25 h. The proposed FTS enables precise and flexible ground freezing in tunnel construction under challenging hydrogeological conditions. Also, it provides an alternative to conventional AGF systems that generally employ external freezing tubes and involve a complex and time-consuming on-site construction process.