Objective When a newly built metro tunnel in water-rich sand strata under-crosses an existing metro station, challenges such as obstacle removal from the existing station's retaining structure, deformation control of the existing station, and water and sand inrush during construction will be encountered. Therefore, it is necessary to study the design and construction schemes for obstacle removal.

Method Based on the project of Wuhan Metro Line 12 interval tunnel under-crossing the existing Yuanlin Road Station of Metro Line 4, the spatial crossing relationship and construction difficulties are analyzed. A retaining structure obstacle removal design and construction scheme for stations adjacent to the first Yangtze River terrace is proposed as follows: first, an obstacle removal shaft is constructed outside the existing station; next, the shaft is excavated down to the shield under-crossing elevation for horizontal freezing and obstacle clearing; then, after backfilling the obstacle removal shaft, shield under-crossing is conducted. Numerical simulation is adopted to analyze the impacts of shaft foundation pit excavation, frost heave and thaw settlement, and shield under-crossing on the existing station. Furthermore, numerical calculation results are compared with field monitoring data to verify the effectiveness of the proposed scheme.

Result & Conclusion Numerical simulation analysis shows that the maximum settlement of Yuanlin Road Station of Metro Line 4 induced by obstacle removal shaft excavation is 3.2 mm, the maximum station uplift caused by ground freezing reinforcement is 2.5 mm, and the maximum settlement induced by shield under-crossing is 1.4 mm, all lower than the allowable deformation limits. The field measured settlement deformation data of the existing station is consistent with the result from numerical simulation, with a maximum measured station settlement of 3.5 mm, meeting deformation control standards. Therefore, the proposed design and construction scheme is safe and feasible.