Dynamic response and energy dissipation of different soil media under touchdown impact of collapsed bodies: Field experiments and numerical simulations

Ground deformation induced by the touchdown impact of collapsed bodies can adversely affect critical structures and facilities, including adjacent buildings, underground pipelines, and metro tunnels. This study investigates the soil deformation induced by collapsed body impact in two typical strata, namely homogeneous soil and stiff-over-soft strata. We conducted model tests for both strata, and established an experimentally validated numerical model using the LS-DYNA finite element analysis software. We analysed the dynamic response characteristics and energy dissipation patterns of both homogeneous soil and stiff-over-soft strata models under the most unfavorable working conditions of touchdown impact loading. Two methods, namely the force–displacement curve method and the Winkler foundation model, were adopted to predict the energy dissipation during the touchdown impact process. Research findings indicated that the dynamic response characteristics of homogeneous soil models under touchdown impact loading were significantly influenced by distance and depth. The majority (approximately 83.37%) is of the impact energy dissipated through plastic deformation of the soil. In stiff-over-soft strata, due to the confinement effect and ’shell effect’ of the concrete slab, localised failure and crack propagation within the slab dominate system energy dissipation, accounting for approximately 61.63% of the total impact energy. When employing force–displacement curves to predict energy dissipation in models directly subjected to impact, both models demonstrated good agreement with simulation results. However, when using the Winkler foundation model to predict energy dissipation in directly impacted models, the homogeneous soil model showed superior agreement. These findings can provide a valuable reference for the safety assessment and the formulation of protective measures for engineering structures affected by the touchdown impact loading of collapsed bodies.