Title: Soil mechanics on-a-chip: granular creep and channelization triggered py porous flow

Author (Talk): Morgane Houssais, City College of CUNY

Abstract:

We present a novel microfluidic design to visualize the dynamics of a 2D, gravity-settled bed of submerged, 400 um polymeric particles, which is subject to an upward flow. The design allows for a precise, metered, interstitial flow, and a high accuracy measurement of the individual particle displacements and the bulk deformation of the bed due to the flow. We have explored two simple configurations. In the first, a homogeneous vertical fluid flow is imposed to a flat and horizontal sediment, and criteria are established for local fluidization — and the subsequent establishment of chimney(s). These experiments allow quantification of small deformations before channelization, in the creep regime triggered by the porous flow. Surprisingly, the small particle rearrangements cause net compaction, even though the porous flow is upward. In a second configuration, we repeat the experiments on a flat bed now tilted at different angles. The system then presents sub-criterion deformation — at angles as low as 3 degrees, with the bulk deformation rate depending on both slope and porous flow strength. The fluid flow and the network of particle contacts appear to be of importance in understanding the observed creep driven by the porous flow and gravity. Future development of this method could allow, 1) similar investigation of further miniaturized systems where cohesion between particles become important, and 2) tracking of both granular deformations and weathering reactions of dissolution and precipitation.