title: Flow-induced compaction of a deformable porous medium.
abstract: Fluid flowing through a deformable porous medium imparts viscous drag on the solid matrix, causing it to deform. This effect is investigated theoretically and experimentally in a one-dimensional configuration. The experiments consist of the downwards flow of water through a saturated pack of small, soft, hydrogel spheres, driven by a pressure head that can be increased or decreased. As the pressure head is increased, the effective permeability of the medium decreases and, in contrast to flow through a rigid medium, the flux of water is found to increase towards a finite upper bound such that it becomes insensitive to changes in the pressure head. Measurements of the internal deformation, extracted by particle tracking, show that the medium compacts differentially, with the porosity being lower at the base than at the upper free surface. A general theoretical model is derived, and the predictions of the model give good agreement with experimental measurements from a series of experiments in which the applied pressure head is sequentially increased. However, contrary to theory, all the experimental results display a distinct and repeatable hysteresis: the flux through the material for a particular applied pressure drop is appreciably lower when the pressure has been decreased to that value compared to when it has been increased to the same value.
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.|Department of Mathematics, University of British Columbia, Vancouver, V6T 1Z2, Canada.
authors.forename: Duncan R
authors.initials: DR
authors.lastname: Hewitt
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.|Department of Engineering Science, University of Toronto, Toronto, M5S 2E4, Canada.
authors.forename: Japinder S
authors.initials: JS
authors.lastname: Nijjer
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.
authors.forename: M Grae
authors.initials: MG
authors.lastname: Worster
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.|Department of Earth Sciences, University of Cambridge, Cambridge CB3 0EZ, United Kingdom.|BP Institute, University of Cambridge, Cambridge CB3 0EZ, United Kingdom.
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Neufeld