APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A16: From Grains to Complex Flows to Sustainable Materials: Soft Matter Meets Climate Change
8:00 AM–11:00 AM,
Monday, March 6, 2023
Room: Room 208
Sponsoring
Units:
DSOFT GSNP
Chair: Vinutha H.A., Georgetown University
Abstract: A16.00003 : Rheological state diagrams for model earth suspensions under shear flow
8:48 AM–9:00 AM
Abstract
Presenter:
Shravan Pradeep
(University of Pennsylvania (UPenn))
Authors:
Shravan Pradeep
(University of Pennsylvania (UPenn))
Paulo E Arratia
(UPenn)
Eric Sigg
(University of Pennsylvania)
Douglas J Jerolmack
(University of Pennsylvania)
Wildfire followed by intense rain on hillslopes causes debris flow. These fast-slowing, dense slurries of earth materials pose threat to human life and infrastructure. These events have been recently exacerbated due the rapidly increasing threat under climate change and associated extreme weather conditions. Recently, we have examined post-wildfire debris from 2018 Montecito mudslides and developed a simple Bingham-type viscoplastic model that could help improve debris flow prediction models in the future. These mixtures were highly heterogenous in nature and as such the interplay between various components in the the debris suspension mixture and their flow mechanics are not completely understood. In this study, we examine model earth mixtures to understand the minimum number of ingredients required to generate complex behavior observed for natural debris flows. We use model mud mixture which contains two components - silica sand and kaolinite clay. An order of magnitude difference in particle sizes coupled with particle shape effects of the constituents create complexity in interparticle interactions. Interplay between frictional (from sand) and attractive interactions (from clay) generate a rich rheological behavior in these model earth mixtures. In pure clay suspensions, yield stress values diverge as concentrations approach the respective jamming point. Increasing the sand content breaks the yield stress divergence and beyond a threshold sand concentration, the yield stress no longer changes with increasing suspension volume fraction. We believe that this non-monotonic behavior in the yield stress with increasing sand concentration is a signature of the change in interactions and associated microstructural changes in the suspension. With increasing sand content, the cohesive contacts between kaolinite particles are lubricated. This reduces the number of average stress-bearing contacts in the suspension and thereby lowering the overall yield stress. Using the steady shear flow curves, we map stress-shear rate state diagrams for suspensions with increasing solid sand content. We anticipate that the framework created for model earth suspensions can be extended to understand the flow regimes in heterogeneous real earth mixtures under steady shear flow.