Instability of Saturated and Unsaturated Coarse Granular Soils: Fid-Bau Portal

Instability of Saturated and Unsaturated Coarse Granular Soils

Zhao, H. F. / Zhang, L. M.

Abstract

It is well known that saturated silt and fine sand are susceptible to instability during undrained shearing. Coarse granular soils may also be unstable during undrained shearing or during rainfall infiltration starting at an unsaturated state. This paper investigates the instability of three saturated and unsaturated granular soils with different fines contents ( $f = 50, 32, and 10 %$ ). Isotropic consolidation tests and mercury intrusion porosimetry tests were first conducted to investigate the instability of the microstructures of these granular soils. Then drained and undrained triaxial tests were conducted to investigate the instability behavior under the saturated condition. Subsequently, wetting tests under the constant shear stress condition were carried out on unsaturated specimens to investigate the instability of the same soils during water infiltration. The instability in the microstructures is in accordance with the compressibility of the soils. The instability during undrained shearing under saturated conditions is described using relations between the state parameter and the peak shear strength or slope of the instability line of the soil. The instability of an unsaturated soil along a wetting path depends on the stress ratio and net confining pressure. Using the equivalent mean effective stress concept, a unified instability line is defined for both saturated and unsaturated soils.