Abstract: During the construction of the Zhongsheng station of the Nanjing Metro Line 7 closely crossing underneath the Line 10, water and sand gushing occurred and the freezing construction affected the deformation of Line 10. Therefore, the metro jet system(MJS) and horizontal freezing method are jointly employed to reinforce the water-rich sandy layer. First, the reinforcement parameters and scope of the combined construction method are determined. Then, the variation patterns of the freezing temperature field, freezing start time, and active freezing time are predicted using numerical simulations. Finally, the soil temperature during the freezing process and the displacement of the existing station floor during freezing and excavation are monitored to provide guidance for optimizing the excavation scheme. The application of the proposed method shows optimal results, and the following results are obtained: (1) During the freezing process, the temperature in the middle is higher than that at the end. (2) The range of the frozen soil wall should be controlled within the MJS reinforcement soil; otherwise, the frozen soil will considerably affect the frost heave deformation. Therefore, a scheme of upper soil sampling and gap freezing could reduce frost heave to some extent. (3) The deformation during the freezing and excavation stages is minimal, thus minimizing the impact on the adjacent existing station structure. (4) The optimized scheme reduces the excavation period from 80 to 66 days.

Key words: metro station, waterrich sandy stratum, metro jet system, horizontal freezing, frost heave deformation