HR: 0800h
AN: T21B-0481    [Abstracts]
TI: How do Material Properties and Sediment Composition Control Shear Strength of Clayey Sediments
AU: * Kock, I
EM: ikock@uni-bremen.de
AF: Research Center Ocean Margins, Leobener Str., Bremen, 28359 Germany
AU: Huhn, K
T21B-0481 AF: Research Center Ocean Margins, Leobener Str., Bremen, 28359 Germany
AB: Mostly unknown during slope destabilisation are deformational processes occurring during the initial phase of failure along a basal shear plane. Major aim of our studies is to analyze mechanical behaviour of a sediment package under low stress conditions. We focus on identification and quantification of influences of sediment composition, material properties, e.g. coefficient of friction, and pore pressure distribution on material strength. We developed a 2D numerical shear box experiment using the Discrete Element Method which is based on a granular model approach. Materials are built up of spherical particles which can be combined to simulate complex grain geometries, e.g. elliptically shaped `clay` minerals. Force distribution is calculated at each particle contact according to simple physical laws. This enables detailed information about local and global stress fields. In addition, particle paths and rotations can be traced at each time step allowing determination of coefficient of friction and porosity as well as identification of spatial and temporal development of localized shear zones. The micro-scaled shear box consists of a fixed bottom wall and an adjustable upper wall to reproduce loads. The model extends over 0.002 x 0.0012m. Particle distribution ranges from `silt` to `clay` fraction. We are using two general model setups. In model (A), `silt` and `clay` particles create a single, heterogeneous layer varying the clay content from 0% - 100%. A three-layered `cake` model (B) consists of a single `clay` layer embedded in a `silt` matrix. Model (A): an increase of` `clay` concentration leads to localization of distinct shear planes. Simultaneously, fluctuations of the coefficient of friction decrease immediately after implementation of `clay`. Shear zones extend along the entire model and are stable over several time steps. Dip angles of shear planes vary between 0°, 25°, and 30°. `Clay` particles rotate into a preferred orientation of 0° to 45° during shear deformation. Model (B): deformation is localized in between the embedded `clay` layer. Shear planes evolve preferred inside the `clay'. However, an intermixing between `clay` and `silt` particles can be monitored along the upper boundary to a certain extent. The lower `silt` displays no movement at all as it is completely decoupled from the `clay` layer.
DE: 3022 Marine sediments: processes and transport
DE: 3070 Submarine landslides
DE: 8000 STRUCTURAL GEOLOGY
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
SC: Tectonophysics [T]
MN: Fall Meeting 2005