The normal impact stiffness of a debris-flow flexible barrier

This paper proposes a normal oriented impact stiffness of a three-supporting cable flexible barrier under a small pretension stress to estimate the structural load behaviour, and employs two categories of small-scale debris flows (coarse and fine) to explore the stiffness evolution through physical model experiments with high-speed photography and load sensing. Results suggest that the particle-structure contact is essential to the normal load effect. Coarse debris flow performs more frequent particle-structure contact and exerts evident momentum flux, while fine debris flows with few physical collisions impart much smaller one. The middle-sited cable that receives only tensile force from vertical equivalent cable-net joint system exhibits indirect load behaviour. The bottom-sited cable shows high load feedback due to the sum of direct contact of debris flow and tensile forces. The relationship between impact loads and maximum cable deflections can be explained by power functions according to quasi-static theory. The impact stiffness is not just affected by the particle-structure contact but by the flow inertia and particle collision effect. Savage number N_sav and Bagnold number N_bag manage to depict the dynamical effects on the normal stiffness D_i. Experiments indicate that N_sav has positive linear correlation with the nondimensionalization of D_i, whilst N_bag has positive power correlation with the nondimensionalization of D_i. This idea is an alternative scope for the study on flow-structure interaction and may contribute to the parameter identification in numerical simulation of the debris flow-structure interaction and the optimization of the design standardization.