The amplifying effect of wood on debris-flow induced impact forces on bridge superstructures

This study examines the impact of wood-laden debris flows on bridge superstructures, focusing on the influence of different bridge profiles (full slab and trough) and log lengths. Using a small-scale physical model, experiments were conducted to measure the horizontal and vertical forces exerted by debris flows with and without wood. The results indicate that the presence of wood significantly increases both horizontal and vertical impact forces on bridge superstructures. The shape of the bridge profile did not significantly affect horizontal and positive vertical impact forces but did influence the magnitude of negative vertical forces. For the full slab profile, however, a measurable influence of the log length on the measured forces cannot be ruled out. The findings underscore the critical role of wood in amplifying impact forces on bridge superstructures, suggesting that bridge designs in debris flow-prone areas should account for the presence of wood to enhance structural resilience and stability. Further experimental studies are recommended to fully understand the interactions between wood-laden debris flows and bridge impact dynamics, and to develop more effective mitigation strategies. • Wood in debris flows doubles horizontal impact forces on bridges compared to flows without wood. • Alignment of wood creates a ‘battering ram’ effect, amplifying localized impact forces. • Log length moderately to largely affects forces, with middle lengths causing higher forces on full slab profiles. • Bridge profile shape impacts negative vertical forces; full slab profiles experience higher values. • Findings stress designing bridges to account for wood's role in amplifying debris flow forces. • Future research should include structural elements like abutments and wing walls for better insights.