Effects of triaxial confining pressure and strain rate on stick-slip behavior of a dry granular material

Some granular materials including spherical glass beads may suffer from stick-slip instabilities which are characterized by successive fluctuations in the stress–strain behavior. Under various loading conditions, these stick-slip failures cause a portion of the stored strain energy within the granular medium to be suddenly released. It is accompanied by a partial collapse and volumetric contraction occurring at the same time. In order to understand the factors behind the stick-slip mechanism, a series of laboratory experiments were carried out in this study. Cylindrical specimens constituted by dry loosely-packed spherical glass beads were tested in triaxial compression. The effects of confining pressure and strain rate on stick-slip behavior were investigated. The experimental results show that as the confining pressure is increased, both the deviatoric stress amplitude and the oscillation amplitude increase. On the other hand, any increase in the strain rate causes the deviatoric stress amplitude to decrease. However, the oscillation amplitude is not affected by the strain rate.