Volume 30, Issue 6 (November 2007)
A Numerical View into Direct Shear Specimen Size Effects
The ASTM D 3080-04 standard, Standard Test Method for Direct Shear Test of Soils under Consolidated Drained Conditions, indicates that the direct shear test specimen width L must be at least ten times larger than the largest particle in the specimen, L/d ≥ 10. The results documented in this note provide visual insight into specimen size and boundary effects through discrete element simulations conducted with numerical specimens ranging in size from L/d = 6.5 to L/d = 177. Particle translation data indicate that in the tested configuration, localized shear zones located far from the specimen boundaries develop only when the specimen size is L/d > 58. The results provide a description of the microstructure evolution during shearing and suggest that the ASTM specimen size criterion may be inappropriate when localized shear banding in uniform granular materials is sought.