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Rechenmacher, Amy1, Nidal Abi Saab1
(1) The Johns Hopkins University, Baltimore, MD

ABSTRACT: Localized Observations of Deformation Band Formation and Behavior in Sands

Shear bands are a ubiquitous deformation feature in dense (dilative) sands in the post-peak regime. Since the post-peak behavior in these materials is strongly influenced by these localized deformation zones, a precise, quantitative understanding of the processes of formation and the behavior within and around persistent shear bands is essential. Recently, an experimental imaging-based technique, Digital Image Correlation (DIC), has yielded highly accurate, local measurements of the deformation fields associated with the onset, growth, and progression of persistent shear bands in sands undergoing plane strain compression. A summary of the observed behaviors will be presented, both for dense as well loose sands. The data suggest that the displacement fields within fully formed shear bands are characterized by coherent, periodic, rotational deformational structures. Such structures may be associated with “force chain” formation and collapse, and also have been evidenced in other geologic materials and numerical- and DEM-based particulate simulations. Acquisition of more detailed experimental evidence of these structures, and development of associated mathematical descriptions, are currently underway, and the results to date also will be presented. Additionally, the DIC technique currently is being extended to local deformation measurement in three dimensions, and preliminary observations of deformation band patterns in loose and dense axisymmetric sand specimens will be offered.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.