Comparison of Cushioning Mechanisms between Cellular Glass and Gabions Subjected to Successive Boulder Impacts

Gabions are the most commonly adopted cushion layer for shielding rigid debris-resisting barriers against boulder impact. Despite the prevalent use of gabions, they comprise heavy rock fragments that are not easily transported up steep natural terrain. The advent of using light-weight cellular glass as an alternative cushion layer provides an innovative approach for absorbing impact energy. However, a lack of insight on their load attenuation characteristics has hindered its potential implementation. In this study, cellular glass was subjected to successive impacts to replicate the dynamic loading of boulders by using a large-scale pendulum setup. Results reveal that for a single impact at 70kJ, crushing exhibited by cellular glass leads to 25% lower impact force compared to gabions, which rely predominantly on rock fragment rearrangement to absorb energy. However, gabions exhibit more effective load spreading, with a diffusion angle three times greater than cellular glass. To ensure robust designs for cellular glass, the Johnson's damage number is proposed to quantify the plastic deformation and to improve estimates of the cushioning efficiency represented by the load-reduction factor (Kc) used in current design.