Dynamics of Debris Flow Impact on Flexible Barriers with Varying Flexibility

Flexible barriers are increasingly recognized for their efficacy in mitigating hazards posed by debris flows; however, the relationship between barrier flexibility and impact response remains poorly understood. Existing design approaches propose an impact equation for flexible barriers without considering barrier flexibility. This study aims to address this gap by investigating the response of flexible barriers with varying flexibilities subjected to debris flow impacts. Physical modeling in a 28-m-long flume facility and its numerical back-analyses were conducted, where barriers of varying flexibilities were tested against debris volumes of 2.5 and 9.0 m 3 . A new dimensionless flexibility number ( N flex ) is introduced to quantify barrier flexibility by considering component stiffness, geometry, and mesh perviousness. Back-analyzed test results reveal that as N flex increases, higher impact pressures are generated in the bottom half of the barrier due to centrifugal forces from debris runup along the deformed barrier. Results also show that the peak normalized impact force exponentially decreases by up to 50% when increasing N flex from 0.07 to 0.36. This study not only reveals that the existing design criterion can conservatively predict the peak impact force on a flexible barrier but also quantifies the degree of conservatism using N flex . Through a newly proposed design equation using N flex , a factor of safety is quantified for the first time, to the best of our knowledge, for peak impact force using an existing design criterion. This new design equation unifies the criteria for estimating impact forces on both rigid and flexible barriers by explicitly incorporating barrier flexibility.