The (In)sensitivity of Granular Creep to Materials and Boundaries

Abstract

AbstractSoils around the planet creep, despite wide variations in particle properties and environments. This sub‐yield “flow” of soil interacts with a variety of boundaries, in terms of geometry and friction. Here we explore the veracity of recent observations of undisturbed, gravity‐driven creep, by testing a suite of materials and boundary configurations in an experimental hillslope. Using an optical interferometry technique, we demonstrate that creep is a generic relaxation process whose qualitative dynamics are insensitive to grain properties. Velocity profiles are exponential, albeit with a defect near the no‐slip boundary. Quantitative patterns such as spatial variability and magnitude of strain rates, however, are exquisitely sensitive to the details of the experiment. The emerging picture is that creep is accomplished by localized plastic failure, which induces an elastic redistribution. Similar patterns have been observed in model glasses and on earthquake faults, indicating that sub‐yield relaxation in disordered materials may share common physics.