Conditions for Compaction Band Formation in Porous Rock Using a Two-Yield Surface Model

by Vennela Challa, Graduate Research Assistant; Dept. of Mechanical and Aeronautical Engineering, Clarkson Univ., Potsdam, NY 13699-5725.,,
Kathleen A. Issen, Assistant Professor; Dept. of Mechanical and Aeronautical Engineering, Clarkson Univ., Potsdam, NY 13699-5725.,,

Serial Information: Issue 9, Pg. 1089-1097

Document Type: Journal Paper

Abstract: (Presented under the title Conditions for Localized Compaction of Porous Granular Materials at the 15th ASCE Engineering Mechanics Division Conference at Columbia University, New York, N.Y., June 2-5, 2002) Compaction bands, a form of localized deformation found in field and laboratory specimens of high porosity rock, consist of planar zones of pure compressional deformation that form perpendicular to maximum compression. Experimentalists report compaction bands and/or shear bands (angled to maximum compression) in high porosity sandstone during a transitional loading regime with multiple active deformation mechanisms. Conditions for localized deformation are determined using a two-yield surface constitutive model and bifurcation theory. The shear yield surface corresponds to a dilatant, frictional mechanism while the cap corresponds to a compactant mechanism. Unlike a single yield surface model, the two-yield surface model predicts both experimentally observed band types for reported values of key material parameters. Observed and predicted shear band angles generally agree. Theory suggests that shear band formation may coincide with activation of the shear yield surface by a previously active cap. If the bulk hardening modulus, k, equals zero (corresponding to localization on the peak or plateau of the mean stress-volume strain curve) compaction band conditions are more favorable than for small positive values of k.

Subject Headings: Terrain models | Porous media | Rocks | Deformation (mechanics) | Compaction (material) | Porosity | Granular materials | Compression | Stress strain relations |

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