Abstract: During shield tunneling process of a metro tunnel in water-rich sandy layer,  rotating body of the shield central body mechanically malfunctioned, thus a safe operating environment should be provided for shield chamber opening and repairing. Herein, a combined vertical excavation face freezing and in-tunnel horizontal freezing method is proposed. Additionally, the design and strength recalculation of freezing curtain, layout of freezing and temperature holes, and freezing construction are elaborated. Finally, based on field tests, the development processes of the temperature field and the frost heave force in soil chamber are discussed in detail. The results illustrate the following: (1) Temperature drop trend of each vertical temperature hole is almost the same during active freezing, whereas the freezing temperature drop rates in different areas vary obviously. The freezing development rate of frozen soil in the freezing pipe rows is 2.8 times higher than that outside the rows due to the influence of superimposed cooling effect. (2) The heat dissipation of the shield machine reduces the temperature of surrounding soil body significantly, thus heat preservation measures should be strengthened. (3) Development rate of horizontal freezing wall is slower than that of vertical freezing wall due to less horizontal freezing pipes and large space restricted by the shield structure. (4) The temperature of the measurement point in the soil chamber is linearly related to depth of hole in soil. The larger the depth of hole in soil of the measurement point, the smaller the effect of heat dissipation of the soil chamber panel, and the faster the cooling rate.

Key words: combined vertical and horizontal freezing, water-rich sandy stratum, frozen wall, shield chamber opening, temperature field, frost heave force