Evaluation of soil fabric using elastic waves during load-unload

Abstract

It is essential to assess the evolution of soil fabric as it has an important role in the mechanical responses of soils during complex loading conditions. This contribution carries out the physical experiments using three granular materials in the laboratory. The variations of compression and shear wave velocities (Vp and Vs) are investigated during load-unload cycles under dry and drained conditions. Supplementary discrete element method (DEM) simulations are performed to understand the evolution of soil fabric during the equivalent load-unload cycles using spherical particles. Vp and Vs are not always reversible even though the stress state regains its isotropic condition after unload, indicating that Vp and Vs are governed by not only the stress state but also the fabric change. The variations of Vp/Vs are density- and stress-dependent; a higher level of stress ratio (σ1′/ σ3′) threshold is observed for denser packings to trigger a significant change in wave velocity ratio (Vp/Vs) for experimental results using spherical glass beads and simulation data using spherical particles. Considering the particle shape, a higher σ1′/ σ3′ threshold is found for more angular particles than rounded particles. The DEM result reveals that Vp/Vs of spherical particles can be correlated linearly with the evolution of fabric ratio (Φver/ Φhor) during load-unload in a pre-peak range under dry and drained conditions.

Keywords

• Soil fabric
• Anisotropy
• Elastic waves
• Discrete element modelling
• Laboratory tests