Numerical modeling of debris flow dynamics considering boulder entrainment, transport, and impulse stress

Abstract

Designing protective structures against debris flows requires knowledge of flow velocity, bed changes, and impact forces. However, few studies focus on boulder entrainment and behavior, pointing to the need for better prediction methods. To address this, a hybrid approach combining grid-based methods (for pressure computation) and particle-based methods (for transport modeling) is proposed. This study uses a numerical model to simulate debris flow in a real scale area. A boulder dynamics module was added to model boulder entrainment triggered by an erosion depth threshold. Model validation was conducted by comparing simulation results with field investigation data, including damage assessments, and boulder entrainment analysis from photographs. The maximum potential impulse stress was calculated using various boulder profiles (diameter and quantity) to assess impulse stress in damaged areas. The developed model reproduced well the dynamic interactions of debris flow and boulders, indicating processes of entrainment, erosion, and deposition. Furthermore, findings revealed that boulder size significantly impacts impulse force, surpassing the influence of boulder quantity. Even with fewer boulders, an increased total mass intensifies debris flow hazards. This study underscores the importance of assessing both boulder size and quantity in landslide-prone areas to develop effective risk mitigation strategies.