HR: 14:25h
AN: T43E-04    [Abstracts]
TI: Deformations of Sediments via Grain-Scale Simulations: A Quasi Static Approach
AU: * Holtzman, R
EM: holtzman@berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering 431 Davis Hall, Berkeley, CA 94720, United States
AU: Patzek, T
EM: patzek@patzek.CE.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering 431 Davis Hall, Berkeley, CA 94720, United States
AU: Silin, D
EM: silin@patzek.CE.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering 431 Davis Hall, Berkeley, CA 94720, United States
AB: Deformation of granular materials such as sediments is highly nonlinear. Consequently, the macroscopic elastic moduli vary with deformation. We quantify these moduli by simulating numerically the deformations of a random disordered pack of spherical grains. In particular, we seek to quantify the impact of hydrate dissociation on the moduli of hydrate-bearing sediments. Our model is discrete, accounting for the interactions between individual grains. For each contact, we calculate the loads using the contact models of Hertz, Mindlin and Deresiewicz. We use a quasi-static model, where deformation is a sequence of static equilibrium configurations of the grains. We find these equilibrium configurations by minimizing a functional which is related to the total mechanical work in the pack. Minimization is obtained using an algorithm based on the conjugate gradient method. Starting with a loose configuration, we simulate a number of loading and unloading cycles. As contact forces develop, we calculate the macroscopic stresses and find the corresponding elastic moduli. The calculated bulk modulus matches published experimental data. We emphasize that this result requires no adjustment of material parameters. The bulk modulus does not vary substantially with different contact models. In contrast, the macroscopic shear modulus is sensitive to the inter-granular microscopic shear. Our simulations allow for analysis of microscopic features such as force chains and contact force statistics, which are extremely difficult to obtain in an experiment. Our model reveals the microscopic mechanisms that lead to the nonlinear, path- dependent stress-strain relations observed in experiments.
DE: 0500 COMPUTATIONAL GEOPHYSICS (3200, 3252, 7833)
DE: 1822 Geomechanics
DE: 4255 Numerical modeling (0545, 0560)
DE: 4524 Fine structure and microstructure
DE: 8020 Mechanics, theory, and modeling
SC: Tectonophysics [T]
MN: 2007 Fall Meeting