Influence of analog barrier type and impact velocity on the energy dissipation of simulant saprolitic rock particles colliding rigid and deformable barrier systems

The analysis of the collision problem of solid objects is of interest in the fundamental study and design of barrier systems protecting infrastructures against debris flows, which can be particularly useful in the sustainable design of transportation systems in urban areas with hilly terrain or extended railway/highway lines which pose additional hazards in relation to landslide and granular flow problems. However, many times debris flows encounter weathered materials in which the formed coating of microparticles on the surfaces of sand grains and fragmented rock alter significantly their contact response. In the present study, we examined with grain-scale tests the impact problem of particle – analog barrier systems encountering natural sand particles in their original form and also in the presence of a laboratory-created soft coating of microparticles, representing simulant saprolitic rock grains. Different types of analog barriers were examined including brittle and ductile rigid blocks and also analog deformable buffering and the data were analyzed in terms of the coefficient of restitution and percentage energy loss expressing the energy dissipation during collision. For impacts on analog rigid barriers, brittle to elastoplastic deformation of micro-asperities comprised a major influencing factor for uncoated sand particles on the energy dissipation during collision, however, additional (and somehow competitive) mechanisms were introduced when coated particles were encountered in the collision tests. Due to the highly hysteretic behavior of the analog deformable barrier, the results converged between uncoated and coated particles in terms of coefficient of restitution and percentage energy loss during collision. For all the combinations of particles and analog barriers, transformation of the translational (input) kinetic energy into different forms also contributed to the dissipation of energy, more prominently for the analog deformable buffering as the deviating angles from the experiments suggested. Additional comparisons were made between 2-dimensional and 3-dimensional analyses of the experiments using one and two high speed cameras, respectively, revealing small differences in the resultant energy dissipation from the two approaches. The results from the present study offer some fundamental insights into the impact problem of particle-block systems and also input parameters which can be further utilized in discrete-based numerical simulations of debris flow – barrier interaction problems.