Tensile stress relaxation in unsaturated granular materials

Abstract

The mechanics of granular media at low liquid saturation levels remain poorly understood. Macroscopic mechanical properties are affected by microscale forces and processes, such as capillary forces, inter-particle friction, liquid flows, and particle movements. An improved understanding of these microscale mechanisms is important for a range of industrial applications and natural phenomena (e.g. landslides). This study focuses on the transient evolution of the tensile stress of unsaturated granular media under extension. Experimental results suggest that the stress state of the material evolves even after cessation of sample extension. Moreover, we observe that the packing density strongly affects the efficiency of different processes that result in tensile stress relaxation. By comparing the observed relaxation time scales with published data, we conclude that tensile stress relaxation is governed by particle rearrangement and fluid redistribution. An increased packing density inhibits particle rearrangement and only leaves fluid redistribution as the major process that governs tensile stress relaxation.

Extensive overview of soil constitutive relations and applications for geotechnical engineering problems

“…The macro behavior is controlled by the coupled HM mechanism owing to the interaction of the two grain-scale phenomena, (1) rearrangement and grain sliding, (2) ruptures of a liquid bridge [ 238 , 239 ]. Noticeable hydro-mechanical coupling is caused by these grain-scale phenomena at the continuum level with extensive investigations in various suction-controlled [ 240 , 241 ] as well as constant water content [ 242 , 243 ].…”

Liquid redistribution in sheared wet granular media

“…This prompts us to look for a liquid migration model in our discrete element method (DEM) simulations where liquid moves between contacts due to shear-driven liquid bridge formation and rupture. Note that liquid transport fluxes are also driven by Laplace pressure changes [24,[26][27][28], either through the vapor phase or through the wetting layers on the beads [29]. However, this mode of liquid transport is excluded from the discussion in this paper.…”