Differences in granular materials for analogue modelling: Insights from repeated compression tests analyzed with X-ray Computed Tomography and image analysis software
Abstract
Six different granular materials for analogue modelling have been investigated using a sandbox with a compressional set-up and X-ray computed tomography (XRCT). The evolving structures were evaluated with image analysis software. The sandbox has one movable sidewall that is driven by a computer-controlled servomotor at 20 cm/h. A 12 cm wide and 20 cm long sheet of hard cardboard was placed on the base of the sandbox and attached to the moving sidewall creating a velocity discontinuity. The whole sandbox was covered on the inside with Alkor foil to reduce sidewall friction. Computed Tomography was used to scan the whole volume in 3 mm increments of shortening until 15 mm maximum deformation was reached. The second approach was a scanning procedure to a maximum deformation of 80 mm in 2 mm increments of shortening for the first 10 mm and in 5 mm increments for the last 70 mm. The short deformation scans were repeated three times to investigate reproducibility. The long deformation scans were performed twice. The physical properties of the materials (table 1) have been described in a previous material benchmark. Four natural quartz sands and two artificial granular materials, corundum brown sand and glass beads, have been used. The two artificial materials were used for this experimental series as examples for very angular and very rounded sands in contrast to the sub-rounded to angular natural quartz sands. The short deformation experiments show partly large differences in thrust angles of both front and back-thrust, in timing of thrust initiation, and in the degree of undulation of thrusts. The coarse-grained sands show smooth and low undulating thrusts that are only affected by the sidewall friction whereas the thrusts in fine-grained sands undulate significantly and partly divide and merge in an anastomosing fashion. The coarse-grained sand thrusts are clearer visualized by XRCT, which indicates a wider shear zone where the material dilates. Furthermore, the reproducibility of the structures in coarse-grained sands is higher compared to the fine-grained sands. The large deformation experiments show similar differences between fine-grained and coarse-grained sands. Reproducibility is better for coarse-grained sands and the thrust spacing and thrust geometry are clearer visible compared to the fine-grained samples. Table 1: Physical properties of analyzed natural quartz sands and artificial sands. Basal friction angles are measured on Alkor foil.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T14B..06K
- Keywords:
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- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting