Abstract
Gauging the mechanical effect of partial saturation in granular materials is experimentally challenging due to the very low suctions resulting from large pores. To this end, a uniaxial (zero radial stress) compression test may be preferable to a triaxial one where confining pressure and membrane effects may erase the contribution of this small suction; however, volume changes are challenging to measure. This work resolves this limitation by using X-ray imaging during in situ uniaxial compression tests on Hamburg Sand and glass beads at three different initial water contents, allowing a suction-dependent dilation to be brought to the light. The acquired tomography volumes also allow the development of air–water and solid–water interfacial areas, water clusters and local strain fields to be measured at the grain scale. These measurements are used to characterise pertinent micro-scale quantities during shearing and to relate them to the measured macroscopic response. The new and well-controlled data acquired during this experimental campaign are hopefully a useful contribution to the modelling efforts—to this end they are shared with the community.
Highlights
1.1 Partially saturated soil behaviourIt is well known that partially saturated soils behave differently to dry and water-saturated soils
This work resolves this limitation by using X-ray imaging during in situ uniaxial compression tests on Hamburg Sand and glass beads at three different initial water contents, allowing a suctiondependent dilation to be brought to the light
The acquired tomography volumes allow the development of air–water and solid–water interfacial areas, water clusters and local strain fields to be measured at the grain scale
Summary
1.1 Partially saturated soil behaviourIt is well known that partially saturated soils behave differently to dry and water-saturated soils. The distribution of the air and water phases in the pore space, governed by capillarity, changes the hydraulic (e.g. decreasing permeability) and the mechanical (e.g. increasing shear strength and stiffness) properties of the granular assembly, as a function of degree of saturation. Based on the early work of Terzaghi, the effective stress concept as a link between the hydraulic and mechanical stress state in soils was enhanced for the application to partially saturated soils by Bishop [8], adding the effect of suction. A recent overview of different CT-based techniques for the investigation of capillary-dominated fluid flow at the pore-scale is given by [33]
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