Abstract: Compared to conventionalconnecting galleries, overlappingconnecting galleries present unique challenges. These include larger frozen volumes, longer excavation and construction times, and more complex freezing hole layouts. To safely and efficiently construct overlappingconnecting galleries in waterrich sandy strata, a freezing scheme is designed based on their structural forms. First, soil samples are collected from the Hesongjie station site of phase II of the Harbin metro line 3. Physicomechanical tests are then conducted at the temperature of －10 ℃. The results reveal a uniaxial compressive strength of 3.53 MPa for silty clay. Then, the thickness of the frozen walls at an average temperature of －10 ℃ is determined. The top and sidewalls are found to be 3.0 m thick, while the collecting well is estimated to be 4.0 m thick. Numerical calculation results illustrate that both the strength and displacement indicators of the frozen walls meet the safety requirements. Moreover, freezing holes are arranged according to the thickness of the frozen walls. A reinforcement method of "vertical freezing on ground and horizontal freezing in the tunnel" is also proposed. The implementation of pressurerelief holes on the ground and horizontal pressurerelief holes in the tunnel effectively control frost heave, limiting it to a maximum of 8.59 mm. This reduces the impact on the surrounding environment. In conclusion, the proposed method ensures the stability of the excavation face and controls frost heave within the allowable range.

Key words: freezingdesign scheme, waterrich sandy stratum, overlappingconnecting galleries, frozen wall thickness, frozen construction