Stress Fluctuations in a Soil Element Testing

Abstract

Soil element testings on the sand grains could result in successive drops in stress-strain relationships. These successive drops and formations give a stick-slip nature to the fluctuations, which might be attributed mainly to the jamming through particles, rate of loading, effective stress, pore fluid characteristics, and the compliance in the apparatus. During the sticking phase, the sand grains are more closely packed and the sample exhibits a gradual increase in stress, however; when the soil matrix becomes relatively unstable, some grains slide out of the column resulting in the stress to sharply drop. The main reason of the jamming might lie in fact that the internal forces do not uniformly propagate through the specimen but are localized through force chains of strained grains. This motion is periodic and might be because of some periodic arrangement of the grains. Following a brief a review of the fluctuations observed during shear tests on granular materials, the GutenbergRichter law has been adapted to illustrate this relationship between the return period of fluctuations and the deviatoric stress amplitude data from a series of triaxial testing results. It has been seen that a plot of logarithm of the return period of fluctuations against deviatoric stress amplitude gives a linear relationship.