HR: 1340h
AN: H53C-1403    [Abstracts]
TI: Granular Flows: A Discrete Look at Particle-Bed Interactions
AU: * McCoy, S W
EM: scott.mccoy@colorado.edu
AF: CIRES and Dept of Geological Sciences, University of Colorado 2200 Colorado Ave UCB 399, Boulder, CO 80309, United States
AU: Tucker, G E
EM: gtucker@cires.colorado.edu
AF: CIRES and Dept of Geological Sciences, University of Colorado 2200 Colorado Ave UCB 399, Boulder, CO 80309, United States
AB: It has been argued that debris flows play a fundamental role in shaping steep topography, yet questions remain about the magnitude of debris flow induced landscape change and the processes by which they erode. If the processes that control the rate at which debris flows and related mass movements cut steep bedrock channels were better understood, prediction of their impact on steepland evolution could be possible. An important control on the erosion of steep bedrock channels is the amount of stress transferred to the bed from the overlying flow. Field evidence from many investigations indicates that impacts from discrete particles could be a major contributor to bedrock erosion, as could particle sliding. To investigate the interaction between a granular flow and the subjacent bed we focus our investigations on three characteristics of a dry granular flow: type of particle- bed interaction (i.e. purely collisional with no slip vs. collisional with slip), dominant flow regime (quasi-static to rapid), and changes in basal stress with measurable flow attributes. We explore these flow characteristics using a Lagrangian discrete element model originally developed by Cundall and Strack (1979). With this type of computer simulation, particle-particle and particle-boundary interactions are modeled explicitly for every particle and boundary in the system. The model is first validated with comparisons to: analytic solutions for single particle impacts, energy conservation for a perfectly elastic system, and documented analog experiments. The model is then used to calculate the relative importance of sliding vs. non-sliding contacts. For each sliding contact the average distance traveled while in contact with the bed is recorded. The dominant flow regime is determined by observing whether force is transferred through enduring contacts and stress chains or via short-lived particle- particle contacts. By identifying the dominant flow regime, the primary mechanism by which force is transferred is recoded as the flow progresses from initiation to deposition. We report on how different field measurable parameters, such as grain size distribution, slope of the bed, and flow thickness, influence the measured basal stress and we show how the basal stress changes as a function of the bed area over which it is measured.
DE: 1810 Debris flow and landslides
DE: 1822 Geomechanics
DE: 1824 Geomorphology: general (1625)
DE: 1826 Geomorphology: hillslope (1625)
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting