Page 13 - CEGE Spring 2023

Hill’s graduate students performing a basin- scale experiment at SAFL
Based on these and other analyses of field data, Hill and her research group develop models and perform basin- scale experiments in the St. Anthony Falls Laboratory and benchtop-scale experiments in the Civil Engineering Building. These experiments support
the importance of mineralogy and
grain size in the pattern of debris flows, which is also indicated in the field. For example, they found that the content
of clay impacts the speed of flows and the apparent avulsion frequency and larger particle size distribution on fans. Changing fine particle content (silt and/or clay) alters avulsion frequencies, erosion behavior, and size sorting behaviors
in the field and in the laboratory, providing critical predictive insights
that can be used to protect human life and infrastructure. Kimberly and her students are then able to combine the results from physical experiments and field observations with computational simulations to understand the physics at play, again, with the goal of improving predictive capability.
Hill points out the importance of cross- disciplinary collaboration with her colleagues in helping advance the field component of her research on natural hazards. “I’m not classically trained in field work and geomorphology, both critical components of this study. My group would be severely challenged
to build such a rich field study without experts in geomorphology and field methodology to lean on. I feel lucky to have colleagues who are interested in bringing together the expertise from my group in particle-fluid flows with theirs in
field data collection, geomorphology, and civil infrastructure problems.” Planned field work includes a 2024 trip with colleagues at Dartmouth to a remote
site in the Aklavik mountain range in
the northern part of the Northwest Territories where changing permafrost
is an issue. In addition, some of Hill’s Taiwanese colleagues have a specific interest in and concern over the problem of building infrastructure in a region
of their country plagued by frequent large-scale debris flows. Hill is currently collaborating with Taiwanese colleagues to develop an international course on natural hazards and civil infrastructure with a field component in Taiwan, which is particularly exciting and builds on her and her collaborators’ expertise.
Hill and her group also collaborate
with researchers in areas beyond
those focused on natural hazards
to study other types of engineered debris flows—drawing physics-based connections between the two. One
of these other areas of application involves a collaboration with structures and pavement colleagues at UMN. Computational modeling of various particle-fluid mixtures in vastly different pavement systems has helped inform the dynamics in mixtures relevant to debris flows. Specifically, hot mix asphalt is compacted with materials made of sand- to gravel-sized particles and
with binders often mixed with clays
and other fine particle materials. Hill’s group investigated the manner in which collaborators in the CEGE structures and pavement groups were able to speed
Hill doing field research.
compaction rates of hot mix asphalt by adding graphene nano-platelets. The addition of graphene nano-platelets increased effective viscosity of the fluid-like asphalt binder mix, providing a thicker, more consistent coating on the gravel sized particles to allow them to more easily rearrange and compact under pressure.
Another area of study models granular road bases, including effects of moisture, with colleagues at UMN, along with David Potyondy, Senior Geomechanics and Software Engineer at Itasca Consulting Group, and John Siekmeier, Research Engineer at the Minnesota Department of Transportation. Hill’s group proposed a way of representing soil moisture efficiently in simulations
of how these granular road bases
flow and settle, and then worked to import this framework into PFC-3D, a commercial code used by the pavement and geomechanics community. Hill
was delighted to learn that Potyondy had entitled this part of the code the
“Hill model.” By 2018, more than fifty researchers on several projects were using this computational framework,
and it was awarded a Research Partnership Award from UMN’s Center for Transportation Studies for “significant impacts on transportation involving teams of individuals.”
Other work by Hill’s group and collaborators on natural and engineered materials include environmental reclamation of oil sands tailings
ponds (funded by Canada’s Oil Sands Innovation Alliance), use of dredged material for wetland restoration (funded by Great Lakes Consortium), and sediment transport (funded by the Office of Naval Research).
Hill is now focusing her primary efforts on her long-term goal of building a deeper, physics-based understanding of complex particle-fluid systems in nature while also including considerations of the communities they affect.
Dramatic landslides can capture popular attention. Kimberly Hill’s work helps us understand the physics behind such dramatic slides and, more importantly, how we might improve prevention efforts and mitigate the consequences.
University of Minnesota College of Science and Engineering | DEPARTMENT OF CIVIL, ENVIRONMENTAL, AND GEO- ENGINEERING 13