Progressive soil collapse and tunnel-system response in an underground complex under varying excavation configurations

Excavation-face instability during deep tunnelling can trigger progressive soil collapse and induce simultaneous deformation of adjacent structures. Existing studies have mainly focused on face stability or the response of individual tunnels. However, it remains unclear how excavation configuration alters soil-collapse propagation and influences the deformation of multiple tunnels within a dense underground complex. To address this gap, a series of full-scale three-dimensional coupled finite element method–smoothed particle hydrodynamics models are established based on a previously validated numerical framework. Excavation-face instability is represented by instantaneous complete loss of face support. The excavation configuration is varied by changing the depth, diameter, and horizontal offset of the excavation face one at a time to examine the resulting changes in soil-collapse propagation, tunnel deformation, soil–tunnel contact pressure, additional internal forces, and performance degradation. A deformation-based assessment framework is further employed to quantify segment-level residual performance and the overall failure degree of the evaluated tunnel system. The results show that the existing structures redirect the propagation of collapsed soil and cause localized deformation and load redistribution. Within the investigated configurations, increasing the excavation diameter is accompanied by a larger absolute disturbed soil volume, more pronounced tunnel deformation and internal-force redistribution, and greater performance degradation, while the effects of excavation depth vary among response measures and tunnels. Changing the horizontal offset primarily shifts the disturbed region and the affected segment ranges.