Turning the corner: How does debris flow path curvature affect the pressure distribution during impact on a rigid barrier?

The impact of debris flows against a rigid obstacle defines the critical loading scenario for structures in the track of a debris flow. The total force imparted by the debris flow on these structures can be approximated using a linear momentum approach. However, this method cannot be used to define the vertical pressure distribution, which is necessary to capture the position of the resultant force. The height of the resultant force is essential in defining the expected failure mechanism (i.e. sliding or overturning) of a structure on impact. Predicting the correct failure mechanism is critical for hazard mapping and emergency response, where estimation of phenomena like structural translation via sliding is needed for appropriate resource deployment.

Although total impact force has been widely investigated, comparatively few studies have reported spatially resolved pressure distributions for debris flow-barrier impacts. Typical empirical methods for the prediction of pressure distributions apply a constant dynamic pressure summed with a linear static pressure. This approach assumes velocity conservation and a circular flow path. However, observations from laboratory studies indicate that this may not always be true. To explore this, laboratory tests were conducted using a dense array of pressure sensors installed in a rigid barrier, impacted by varied releases of water and water-sediment mixtures. These experiments offer pressure measurements at high spatial and temporal resolution, correlated with visual high-speed camera data used to define the flow path and velocity field within the control volume.

Flow paths with variable velocity and curvature were observed for a range of material compositions. Based on these observations, a novel analytical model is proposed to predict pressure distributions using generalized approximations of the rate-of-change of flow properties and path curvature. This approach provides equivalent total force predictions to traditional linear momentum models but allows for direct determination of the position of the resultant force.