Rheological fingerprints of non-inertial debris flows

Climate change has exacerbated the frequency of landslide events causing huge loss to human life and infrastructure. One major challenge in predicting such events is the absence of constitutive models to explain the flow and failure properties of natural heterogeneous dense suspension mixtures. From a suspension rheology perspective, the onset of a landslide is dictated by the rearrangement dynamics of the constituent materials and the magnitude of external forcing. Here, we use a minimum ingredient complex fluid mixture - a suspension of silica sand and kaolin clay suspended in deionized water - to probe the effect of material properties on the yielding phenomena in dense suspensions. Silica sand particles primarily interact through frictional contacts, while the kaolin clay particles are attractive and form system-spanning percolated structures. We systematically vary the clay to total solids (clay ratio), and the overall suspension volume fraction to generate steady shear rheological flow curves. By re-scaling the curves using yield stress and microscopic rearrangement times, we obtain universal yielding curves that only depend on the clay ratio parameter. By estimating the strain energy required to fluidize the mixture, we show that the sand-rich suspensions are “annealed” and exhibit more “brittle-like” yielding behavior compared to the clay-rich suspensions. Here, we developed a preliminary rheological framework to explore the effects of frictional interactions in model mud mixtures using a minimum ingredient complex fluid. We believe that our work reconciles previously contradictory observations in debris flow rheology and can help modify the existing models that assess the hazard potentials of extreme environmental flows in the future.