Mitigation of boulder-laden debris flow impacts on frame structures using an EVA cushion layer: A numerical study

This study investigates the impact effect of boulder-laden debris flows on frame structures, aiming to propose an innovative protection strategy—installing an ethylene-vinyl acetate (EVA) cushion layer on the impacted surface—and verifying its disaster mitigation mechanism through numerical simulations. A coupled numerical model of 1.0‑m boulders and the frame structure were developed to compare the dynamic responses of the structure with and without the cushion layer at impact velocities of 8 m/s, 10 m/s, and 12 m/s. The results show that the EVA cushion layer reduces the peak impact force on the structure by 38%–52%, and its energy dissipation performance is more effective at higher flow velocities. Under a 12 m/s impact, the unprotected structure suffers weld fracture and beam-column buckling, whereas the system with the EVA cushion layer only undergoes local plastic deformation, with the critical displacement reduced by up to 68%. Mechanistic analysis confirms that the buffer layer suppresses stress wave propagation by extending impact duration and enhancing interfacial damping, thereby effectively converting boulder kinetic energy into elastic deformation energy. This study proposes a novel energy‑absorbing protection solution for frame structures in debris flow‑prone areas, offering significant practical value for enhancing the disaster resilience of mountainous engineering projects. Moreover, the numerical framework and quantitative findings provide a basis for optimizing cushion thickness and material properties in future engineering applications.