Classic, modern, and physics-based rheological laws for geophysical granular flows in a landslide hazard chain

Abstract

Geophysical granular and particle-laden flows, in a typical landslide hazard chain, pose significant risks to human life and infrastructure. The governing rheological constitutive law of the flowing mixture plays a crucial role in assessing their mobility and consequences. Developing a generic constitutive law, capable of capturing the evolving nature of mixture properties across different flow regimes in a landslide hazard chain, requires the incorporation of several physical concepts and is an active research question. This technical review presents a comprehensive review of existing rheological laws by classifying them into classic, modern, and physics-based mixture laws. Firstly, a preliminary classification of particle-fluid mixtures is proposed, encompassing dilute, moderate, and high ranges of solid concentrations. Next, following the continuum mechanics, the various types of particle-fluid mixture representations, from single-phase to multi-phase conceptualizations are presented. With a focus on flow index classification, the classic laws that assume a fixed relation over a single flow regime are explored. By switching to different flow regimes, rather than flow indexes, the modern laws that aim to capture the rheological behavior of flowing mixtures across different flow regimes are reviewed. Finally, the physics-based mixture rheological laws which combine the existing classic and modern rheological laws for fluid and solid phases, and further include additional novel rheological laws for interphase interaction forces, are reviewed. This review enlightens the existing research trends on classic and modern rheological laws, describes their capabilities, and highlights missed concepts that are required for the development of a generic rheological law for landslide hazard chains. Enhanced understanding of the evolution of rheological behavior of flowing mixtures over various flow regimes in a landslide hazard chain improves further studies on hazard simulation and prediction, risk mitigation, and land use planning.