Seismic Stability of Dual Tunnels in Cohesive–Frictional Soil Subjected to Surcharge Loading

In this study, a self-developed adaptive finite element limit analysis (AFELA) code was adopted to explore the stability of dual tunnels in cohesive–frictional soil subjected surcharge loading and seismic action. Parametric studies different influential factors, including depth tunnels, horizontal distance between acceleration coefficient, unit weight, cohesion internal friction angle soils, were conducted using AFELA code. An meshing technique for optimal accuracy efficiency, pseudostatic method used simulate Strict upper bound (UB) lower (LB) results with relative errors less than 7% acquired. Detailed design tables presented facilitate engineering design, three typical failure patterns, single side-wall failure, half-cross-shaped cross-shaped corresponding stable levels, summarized deeper insight into how mechanism evolved under conditions. The indicated that variations weight void affected bearing capacity almost linearly. Furthermore, tunnel system is vulnerable actions, further undermined by adverse effects additional seismic-caused interactions two adjacent tunnels.