A review and analysis of granular shear experiments under low effective stress conditions

Abstract

The constitutive law for granular materials is governed mainly by the intergranular friction, which depends strongly on the gravitational force or effective isotropic stress. Such experiments are mostly performed with relatively high effective isotropic stress. This fact poses serious limitations on the formulation of a materially objective constitutive model based on experiments performed on earth. This paper analyzes the limited experimental data of shear strength and rheology of granular materials, subject to low effective stress conditions obtained in microgravity μg as well as in 1 g conditions. Results from these experiments show that granular materials may have an extremely high macroscopic peak friction angle and clear nonlinear S-shape non-Bingham fluidity in low effective stress conditions. In this paper, the classical limit equilibrium method is employed, and a rheological constitutive model is used to study experimental data. The limit equilibrium method enables the authors to correlate the bearing capacity of sand foundation with high peak friction angles under varying effective stress conditions. The calibrated analytical solution for the rheological constitutive model under low effective stress conditions, predicts a clear S-shape correlation of the viscous shear stress and shear strain rate. The mutation or inflection point takes place around the in-situ Niigata earthquake shear strain rate. The results of this paper are of great relevance to the assessment of seismic liquefaction hazards of infrastructure on earth.