Three-dimensional numerical investigation of ground settlement caused by side-by-side twin tunnels

Abstract

A parametric study using 3D finite element analyses was conducted to investigate settlement behavior and interactions between side-by-side twin tunnels during excavation. The study considered six cover-to-diameter (C/D) ratios, ten pillar-to-diameter (P/D) ratios, and two construction sequences. The total settlement of the excavated twin tunnels and the settlement induced solely by the new second tunnel were analyzed. Validation was performed by comparing results with published case studies, showing trends consistent with existing literature. Key findings include: (1) greater cover depth produces a wider settlement trough and reduces second tunnel-induced settlement, though total settlement slightly increases; (2) cover depth significantly affects second tunnel-induced settlement, while pillar width impacts total settlement; (3) concurrent excavation causes slightly higher settlement and a deeper, wider trough compared to staggered excavation; (4) lower cover depths result in higher settlement increase rates. Finally, two design charts are proposed to estimate settlement from the second tunnel and the eccentricity of the maximum total settlement relative to the center of the new tunnel.