Granular materials, such as sands, pharmaceutical pills, and grains in a silo, manifest quite intriguing behavior: they are comprised of solid particles and behave as solids under static loading; but upon the initiation of instability, they flow like liquids. Science magazine recently has cited the lack of a general theory for the motion of granular materials as one of the top 100 currently unanswered questions in science. This Faculty Early Career Development (CAREER) project aims to contribute to the pursuit of better understanding of granular material behavior by looking at the problem of localized, dense granular flow. The problem will be studied in three contexts: the geomechanics of shear banding in sands, the role of fault gouge in the initiation of earthquake faulting, and the quantification of thermodynamic variables for dense granular flows. Specifically, we will use experimental imaging techniques to detect and characterize micro- and meso-scale deformations that are presumed to be signatures of the buildup and collapse of grain columns, which form the basic mechanism for stress transfer in granular materials. Due to the innate opacity of granular systems (e.g. sand, corn), most previous studies have been limited to 2D realizations of idealized materials. This effort will provide a first-of-its-kind opportunity to characterize granular flow in a real material by imaging sand as it deforms along glass boundaries.
An improved understanding of granular material behavior will broadly impact a host of science and engineering problems involving granular materials, such as improved quantification of safety margins in geotechnical failures, preventing grain clogging in silo flow, and improved predictability of earthquake nucleation. The cross-disciplinary fertilization deriving from this effort will serve to heighten scientific discovery in each of geomechanics, geophysics, and granular physics. The educational component of this research effort capitalizes on the image-based nature of the proposed experiments to create avenues for visualization of failure and flow phenomena in granular materials, for use in undergraduate courses, K-12 outreach and continuing education. The research activities will directly involve undergraduates, and will particularly target women in conjunction with USC?s Women in Science and Engineering (WiSE) program.
