Objective During the construction of ultra-close overlapping metro tunnels, the small clearance between tunnels often leads to uneven settlement deformation. Therefore, it is necessary to investigate the mutual disturbance patterns and relevant control measures for the construction of such tunnels.

Method Taking the project of the overlapping section from Guangfudadao Station to Chongqing East Station of Chongqing Metro Line 27 under-passing the East Extension of Chongqing Metro Line 6 as a case study, the full-process construction excavation is simulated. The mutual influence patterns during construction and the deformation characteristics between the tunnels are analyzed. Based on this, a section with the minimum clearance between the tunnels is selected as the research object to study the optimal grouting reinforcement measures, which are then applied to the actual engineering project.

Result & Conclusion After the under-passing construction is completed, the settlement deformation of the existing tunnel increases with the decrease of the clearance between the overlapping tunnels. After the over-passing and under-passing constructions, an interactive superposition effect occurs on vertical displacement between the tunnels. After implementing the segment backfill grouting reinforcement measure for the shield tunnel, the settlement values of both the mined tunnel and the shield tunnel are effectively controlled. The vault settlement values of the segments for Chongqing Metro Line 27 and Line 6 are reduced by 37.7% and 56.0%, respectively. Analysis results of the on-site monitoring data show that after implementing reasonable construction control measures, the overall deformation of the tunnel structures is effectively controlled, ensuring the structural safety of the tunnels.