A new pre-supporting technology named the freeze-sealing pipe roof (FSPR) method was adopted in the construction of Gongbei tunnel (Zhuhai, China), a critical part of the Hong Kong–Zhuhai–Macau bridge (HZMB) project. The method combined pipe-roofing with artificial ground freezing (AGF). The pipe roof which included a number of large-diameter steel pipes was designed to play a primary role in load bearing, while the frozen wall between pipes was designed for water sealing. The refrigeration proceeded in two stages called the active freezing period and excavation period. This paper mainly focuses on the freezing characteristics of FSPR to explore how the frozen soil wall developed and changed over time during both periods based on field temperature data. The results show that the development of the frozen wall met the design requirements in fewer than 80 days of refrigeration considering the most unfavorable situation. The distribution of frozen soil along the entire tunnel was non-uniform. Frost heave and thaw weakening problems should be taken into account, since some of the bottom section of the frozen wall was more than 3 m. The frozen soil at the excavation side was visibly influenced by the replenishment of heat due to excavation, while the frozen soil outside the excavation face was much less influenced. The thermal effects of Hurricane Nicole on the frozen soil wall was also observed. The conclusions provide experience, reference, and guidance for the development of similar projects in the future.

The pipe jacking method is gradually attracting increasing levels of attention and is becoming an important method for constructing underground engineering. However, jacking large-size concrete pipes in urban core areas subjected to complicated geological conditions is still a big problem preventing the employment of the pipe jacking method, and further studies related to pipe jacking are required. This paper presents a case study on the construction of three parallel large-size reinforced concrete circular pipes in the upper-soft and lower-hard composite formations, in which the construction work was implemented using the slurry balance pipe jacking method with the sequence of jacking the 1# and 3# pipes prior to the 2# pipe being implemented in field construction. This case study was implemented by employing numerical simulations with the aforementioned pipe jacking sequence, which focused on the stress and deformation variations of the reinforced concrete circular pipes, as well as the vertical settlement of the ground surface during the jacking processes, and considering the influences from the excavation pressure and grouting pressure of the drag-reducing thixotropic slurry. The simulation results revealed that a higher excavation pressure from the pipe jacking machine can easily induce an excessive pushing and squeezing effect of the excavated soil with the uplift phenomenon, while the increasing grouting pressure can be used to reduce the overall vertical settlement of the ground surface, whereas an excessive grouting pressure may have no effectiveness on protecting the reinforced concrete circular pipes. This work provides the numerical foundations for investigating the behavior of jacked parallel large-size reinforced concrete circular pipes.

A new presupporting technology named freeze-sealing pipe roof (FSPR) method was adopted in the construction of Gongbei tunnel (Zhuhai, P.R. China), which was a critical part of Hong Kong-Zhuhai-Macau Bridge (HZMB). The method combined the pipe-roofing with artificial ground freezing (AGF). The water resistance performance of FSPR surrounded by water-rich soils was studied based on the field temperature data. The time-dependent temperature changes of the frozen soil between two adjacent pipes were presented, and the thicknesses of the frozen soil in different freeze period were calculated. Besides, the remote temperature monitoring system used in this field research was presented systematically. The thermal effects of the Hurricane Nicole on the frozen soil wall were also observed. The results showed that the closure of frozen soil wall can be classified into two different modes. The frozen soil between the pipes before excavation had met the design requirements before excavation, and the FSPR maintained satisfied water resistance performance.