Study of water flow under gravity and pressure through granular solids

<p> These experiments concern the movement of water through soil. The principal variable of interest is the volume of water that has passed vertically through a column of soil observed at regular time intervals. The core of the experimental apparatus is a vertical tube (the test section) that is roughly 2 m long with a 3.18 cm inner diameter. The lower portion of the test section is filled with a sample of soil (200 mL) followed by a volume of water (1200 mL). In each experiment, this water is allowed to pass downward through the soil sample and out through a 0.95 cm diameter hole. From there, expelled water passes through a short flexible tube into a collection beaker. The volume in the collection beaker is monitored by an automated system with a sampling frequency of 10 Hz. More accurately, the level of water in the beaker is monitored with a laser ranging device, the beam of which is reflected off of buoyant opaque particles -- flakes of dried parsley -- that remain on the surface as the beaker fills. The apparatus is also fitted with a system for pressurizing the test section to a constant pressure up to a maximum of around 1200 hPa (1.2 atm).</p>