  Predicting rapid and slower soil evolution remains a scientific challenge.
This process involves poorly understood aspects of disordered granular matter
and dense suspension dynamics. This study presents a novel two-dimensional
experiment on a small-scale chip structure; this allows the observation of the
deformation at the particle scale of a large-grained sediment bed, under
conditions where friction dominate over cohesive and thermal forces, and with
an imposed fluid flow. Experiments are performed at conditions which span the
particle resuspension criterion, and particle motion is detected and analyzed.
The void size population and statistics of particle trajectories bring insight
to the sediment dynamics near fluidization conditions. Specifically, particle
rearrangement and net bed compaction are observed at flow rates significantly
below the criterion for instability growth. Above a threshold, a large vertical
channel through the bed forms. In the range of flow rates where channelization
can occur, the coexistence of compacting and dilating bed scenarios is
observed. The results of the study enhance our capacity for modeling of both
slow dynamics and eventual rapid destabilization of sediment beds.
Microfluidics channel soil-on-a-chip studies open avenues to new investigations
including dissolution-precipitation, fine particles transport, or
micro-organisms swimming and population growth, which may depend on mechanics
of the porous media itself.
