Velocity Attenuation of Granular Debris Flows During Impact on Rigid Barriers

Abstract

Effective design of rigid debris-resisting barriers remains a challenging problem for practitioners. At present, a pseudo-static approach is commonly used for the estimation of debris impact loads acting on barriers. In this approach, the dynamic impact pressure is estimated using the hydrodynamic equation and an assumed value of the dynamic pressure coefficient. The bulk density and travel velocity of the landslide debris are also required for the calculations. To this end, the debris velocity under free-field conditions can be obtained from a conventional debris mobility assessment. A limitation of this approach is that it ignores the attenuation of the debris’ velocity during the deposition process behind the barrier. To provide a scientific basis for assessing the velocity of granular debris flows during impact on rigid barriers, this paper presents results of debris velocity from a laboratory study of debris-barrier interaction using physical flume modelling. High-speed cameras were used to capture the dynamic motion of the flowing debris. The images obtained were analysed using the particle image velocimetry (PIV) technique to estimate the velocity of the debris. The results show that, following the first stage of impact, the accumulated debris behind the model barrier formed a stationary zone and caused the remaining debris to slow down in a run-up process. As a result, the peak debris momentum was 30% lower compared to that observed under free-field conditions. The findings of this study will allow practitioners to optimise the design of debris-resisting barriers in the future.