Blast Wave Transmission in Full-Scale Multi-Node Tunnel Networks: Interaction Regimes, Wave Recompression, and Scaling Deviation

Blast-wave transmission in underground tunnel systems is strongly affected by sequential geometric discontinuities, yet most previous studies have focused on isolated tunnel components or short-distance propagation. This study investigates pressure transmission behavior in a 100 m full-scale multi-node tunnel network subjected to near-field external detonation. The network contains elbows, branching junctions, and cross-sectional transitions, representing a realistic underground protective access system. Numerical simulations were conducted using a validated arbitrary Lagrangian–Eulerian blast-analysis framework for 10 kg, 100 kg, and 500 kg C-4 charges. The validation lineage of the numerical framework, together with the mesh-sensitivity basis adopted in the present model, is summarized explicitly in the Methods section. To distinguish local geometric interaction from quasi-independent propagation, two spacing regimes were defined according to the hydraulic diameter of the tunnel. A Node Interaction Index (NII) was introduced to quantify the deviation between coupled multi-node transmission and independent attenuation prediction. The results show that closely spaced discontinuities produce wave recompression, extended positive-phase duration, and locally amplified peak pressure, whereas larger spacing leads to near-independent attenuation behavior. Comparison with conventional cube-root scaling further reveals a sustained deviation range in the full-scale tunnel network, indicating that classical similarity relations are conditionally valid in confined long-distance propagation. Across the three charge weights, the spatial pattern of interaction remains similar, while the persistence of impulse-related deviation becomes more pronounced as charge weight increases. The proposed interaction-aware framework provides a practical basis for blast-resistant assessment and design of underground protective tunnel systems.