HR: 0800h
AN: T21B-0473    [Abstracts]
TI: Micro-structure evolution in sheared granular material
AU: Sakaguchi, H
EM: sakaguchih@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: * Hori, T
EM: horit@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Yoshioka, N
EM: yoshi@yokohama-cu.ac.jp
AF: Yokohama City University, Seto 22-2, Kanazawa-ku, Yokohama, 236-0027 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AB: In order to study the relationship between microstructure evolutions and shear resisting mechanisms in granular materials, computer simulations of a gouge layer under shearing condition were performed using the three dimensional Discrete Element Method (DEM). The details of the simulation conditions follow the laboratory experiment presented by Yoshioka and Sakaguchi in this meeting. Monitoring inter particles forces for all contacts indicates that there is a significant increase in heterogeneity in contact force distribution_@with increase in shear loading. Large compression forces make contacts more rigid, and rigid contacts can resist to larger forces. As a result, rigid column-like microstructures are formed in the direction of the major principal stress which is the direction of superimpose of the normal force and the shear force on the upper block. Those columnar structures resist to shearing locally. However, we found that there is a life-time limitation in such columnar structures formed in sheared granular materials. When a rigid columnar structure rotates or deflects due to couple stress induced from shear load, it loses the resistant strength to shearing, because its direction is no longer equal to the direction of the major principal stress. Consequently, the columnar structure starts to collapse. The rigid columnar structure rotation is accompanied by two cases. One is the case when a larger number of particles are involved in one columnar structure. In this case, larger moment acts on a constant couple force due to shearing. The other case is that a purely larger couple force acts on a columnar structure. From this microstructural analysis, we can conclude that the behavior of sheared granular materials is profoundly controlled by the evolution in forming and collapsing of the columnar structures. In addition, the thickness of shearing layer is also controlled by the length of the columnar structures which have a certain upper limit.
DE: 8010 Fractures and faults
DE: 8034 Rheology and friction of fault zones (8163)
SC: Tectonophysics [T]
MN: Fall Meeting 2005