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DEM Simulation of Direct Shear: 2. Grain Boundary and Mineral Grain Strength Component Influence on Shear Rupture

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Abstract

The influence of mineral grain and grain boundary strength is investigated using a calibrated intact (non-jointed) brittle rock specimen subjected to direct shear with a particle-based distinct element method and its embedded grain-based method. The adopted numerical approach allows one to independently control the grain boundary and mineral grain strength. The investigation reveals that, in direct shear, the normal stress (σ n) applied to a rock specimen relative to its uniaxial compressive strength (UCS) determines the resulting rupture mechanism, the ultimate rupture zone geometry, and thus its shear stress versus horizontal displacement response. This allows one to develop a rupture matrix based on this controlling parameter (i.e., σ n/UCS). Mineral grain strength reductions result in the lowering of the apparent cohesion intercept of the peak linear Coulomb strength envelope, while grain boundary strength reductions change the peak linear Coulomb strength envelope to a bi-linear or curved shape. The impact of grain boundary strength is only relevant at σ n/UCS ratios <0.17 where tensile and dilatant rupture mechanisms dominate. Once shear rupture begins to be the dominant rupture mechanism in a brittle rock (i.e., at σ n/UCS ratios >0.17), the influence of weakened grain boundaries is minimized and strength is controlled by that of the mineral grains.

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Acknowledgments

This research was supported by the Centre for Excellence in Mining Innovation (CEMI) and the Natural Sciences and Engineering Research Council of Canada (NSERC). Constructive and helpful comments by the reviewers, which improved the manuscript, are also acknowledged.

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Authors and Affiliations

  1. Department of Civil Engineering, University of Toronto, 35 St. George, Rm 105, Toronto, ON, M5S 1A4, Canada

    R. P. Bewick & W. F. Bawden

  2. Centre for Excellence in Mining Innovation (CEMI), 935 Ramsey Lake Road, Willet Green Miller Centre, Sudbury, ON, P3E 2C6, Canada

    R. P. Bewick & P. K. Kaiser

  3. Mirarco Mining Innovation, Laurentian University, 935 Ramsey Lake Road, Sudbury, ON, P3E 2C6, Canada

    R. P. Bewick

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  1. R. P. Bewick
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  2. P. K. Kaiser
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  3. W. F. Bawden
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Correspondence to R. P. Bewick.

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Bewick, R.P., Kaiser, P.K. & Bawden, W.F. DEM Simulation of Direct Shear: 2. Grain Boundary and Mineral Grain Strength Component Influence on Shear Rupture. Rock Mech Rock Eng 47, 1673–1692 (2014). https://doi.org/10.1007/s00603-013-0494-4

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  • DOI: https://doi.org/10.1007/s00603-013-0494-4

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