Objective The dynamic excavation of ultra-deep foundation pits will impose impacts on adjacent existing metro stations, leading to structural deformation or settlement of the stations, and even endangering structural safety and disrupting normal metro operation. Accordingly, it is necessary to formulate a reasonable reinforcement scheme during excavation to mitigate the above-mentioned impacts on existing stations.

Method Based on the ultra-deep foundation pit project adjacent to an existing metro station of Chengdu Metro Line 18, three grouting reinforcement schemes targeting horizontal deformation control, vertical deformation control and overall deformation control are proposed. Numerical simulation is adopted to compare and analyze ground settlement and structural deformation responses of the existing station under different reinforcement schemes, and field monitoring data are used to verify the reinforcement effect.

Result & Conclusion  Before adopting reinforcement measures, the maximum ground settlement at the midpoint of the foundation pit long side reached 18.70 mm, and the differential settlement of the existing station standard section was 4.67 mm. With the adoption of the L-shaped grouting reinforcement scheme for overall deformation control, the maximum ground settlement decreased to 6.38 mm, a reduction of as much as 65.89%, and the differential settlement of the existing station standard section dropped to 1.57 mm, representing a 66.42% reduction. Numerical simulation results are in good agreement with field monitoring data, demonstrating that the L-shaped grouting reinforcement scheme can effectively restrain stratum deformation and structural settlement induced by the ultra-deep foundation pit projects adjacent to existing metro stations.