Experimental Study of the Dynamic Response and Energy Dissipation Characteristics of Silica Sand and Sandy Soil under Multi-impact Loading

To investigate the dynamic behavior of granular materials under repeated impact loading, repeated compression tests were conducted on sandy soil and silica sand using an improved Φ40 mm split Hopkinson pressure bar (SHPB) setup. The study systematically examined the evolution of material density, particle breakage, stress wave propagation, stress–strain response, and energy dissipation characteristics. The results indicate that the density of both materials increases gradually with the number of impacts and eventually stabilizes. The median particle size of sandy soil decreases by only approximately 25 %, whereas that of silica sand reduces by up to 65.6 %. After five impacts, the relative breakage indices of sandy soil and silica sand are 0.05 and 0.23, respectively, indicating a more pronounced particle refinement effect in silica sand. Wave velocity measurements show that both the compression wave and peak stress velocities of sandy soil are more sensitive to densification, while silica sand exhibits limited increases in wave velocity due to severe particle breakage. Regarding stress–strain behavior, both materials undergo elastic, plastic, yielding, and strain-hardening stages, with overall stress levels shifting upward as the number of impacts increases. However, due to particle breakage, silica sand exhibits greater energy dissipation, resulting in lower stress levels under the same strain compared to sandy soil. Energy analysis reveals that the energy absorption density of both materials first increases and then decreases with initial density. Notably, silica sand demonstrates more stable and progressively enhanced energy dissipation over five impacts, making it more suitable for protective applications under repeated impact loading. The findings provide experimental evidence and theoretical support for the design and application of granular materials in protective engineering and related cushioning structures.