Factors affecting sand behavior in constant deviatoric stress loading

A rise in pore water pressure within a soil mass leads to a decrease in the mean normal stress, while the vertical load due to soil weight remains unchanged. Such loading may be represented in the triaxial apparatus by a test in which a constant weight is applied to the top of the soil sample, while the confining stress is gradually reduced, and may be referred to as a Constant Deviatoric Stress (CDS) loading. Under such loading, loose dry sand initially experience small volume increase, and then start to contract substantially until failure is reached. In saturated sand, such contractions can lead to the generation of pore water pressure and substantial loss of strength, which can in turn result in catastrophic flow-type failures. This study examines factors that affect the volume contractions in CDS loading. Tests were carried out on dry and saturated samples of a local sand in order to determine the effects of the various factors on the sand behavior in CDS loading. The study showed that void ratio, confining pressure, applied deviatoric stress, anisotropic consolidation, and method of sample preparation affect the volume contractions of dry samples. Two other sands were also tested in order to examine the effects of sand type and angularity.