Particle damage observed in ring shear tests on sands

In this paper, particle damage of three test sands with different mineralogical compositions is studied using stress-displacement response measured in ring shear tests, particle-size distributions of the original sand prior to shear and from the shear band after shear, and by examining particle shape changes determined by scanning electron microscope. Particle damage during shearing produced a wider particle-size distribution, and damage typically continued until the normal stress was small (about 28 kPa) in constant volume ring shear tests and the internal stresses were distributed among sufficient particle contacts such that damage practically ceased. The dominant damage mechanism (typically either particle abrasion and shearing-off asperities or particle splitting) depended strongly on the soil response (i.e., contraction or dilation), particle hardness, and particle-size distribution, but both mechanisms produced particles that were more angular and rougher than the original sand particles. The magnitude of particle damage observed in the ring shear tests was influenced by the consolidation normal stress, shear displacement, particle mineralogy, particle-size distribution, drainage conditions, and soil fabric (in constant volume tests). Lastly, the influence of particle damage on engineering properties including hydraulic conductivity, liquefaction resistance, stress-strain response, friction angle, and critical state are briefly discussed.