Stress Fluctuations in Triaxial Testing Of Angular Grains

Stress fluctuations caused by stick-slip instabilities are frequently encountered in laboratory shear testings of granular materials. It is not common to observe stick-slips in angular-shaped granular assemblies, although rounded particles are more prone to this type of behaviour. This paper specifically concerns the deviatoric stress fluctuations in the shearing of coarse angular glass granules. A systematic experimental program comprising triaxial compression tests was realized to investigate the effects of particle size, confining pressure, and strain rate on the stick-slip mechanism. Particle size effect was examined by adopting three separate size distributions. In order to understand the influences of testing conditions on the stress fluctuations, the specimens were tested under four different confining pressures and by applying two distinct strain rates. The results showed that both the particle size and confining pressure greatly affected the stress fluctuations whereas the influence of strain rate was unclear.