Debris Flows over Bumpy Bed: Experiments and the Constitutive Modelling

Debris flow is one of the most destructive natural hazards which is typically distinguished by high solid content and significant interactions between the particles and interstitial fluid. This study focuses on fundamental inter-particle interaction pattern and the underlying mechanism in typical debris flows over bumpy bed with varying bed inclinations. Internal dynamic parameters of the debris flows are obtained based on the refractive index matching (RIM) technique and non-invasive sensor networks. It is found that the granular interaction pattern is vertically stratified with the near-bottom particles intensely colliding with each other in a gas-like state, while the near-surface particles sliding collectively in a solid-like state. Based on the observed flow behavior and measured parameters, a multi-state constitutive model is proposed, which incorporates the kinetic theory for the collisional stress and a newly developed frictional stress model. This constitutive model improves the overall granular stress modelling accuracy for the debris flow with highly heterogeneous flow structures.