HR: 1330h
AN: H22A-0902 INVITED     [PDF]
TI: Centrifugally Driven Flow in Diverse Porous Media Over Wide-Ranging Moisture Conditions
AU: * Nimmo, J R
EM: jrnimmo@usgs.gov
AF: USGS, 345 Middlefield Road MS-421, Menlo Park, CA 94025 United States
AU: Caputo, M C
EM: caputo@area.ba.cnr.it
AF: Water Research Institute - IRSA - CNR, Via F. De Blasio, 5, Bari, 70123 Italy
AB: Centrifugal force has been successfully applied to measurement of saturated and unsaturated hydraulic properties of soils and rock. The basis of most methods is to apply a steady flow of water, by either a constant head or a metering pump, to a sample in a centrifuge. If the centrifugal force is great enough to constitute the dominant driving force, measurements of the steady-state flux, water content, and matric pressure can yield highly accurate values of hydraulic conductivity and water retention. The great force permits measurement of properties and conditions that are otherwise impossible or impractical. For example an experiment lasting a few days can measure unsaturated conductivity as low as 1E-9 cm/s. Our new approach expands the range of media and conditions to which centrifugal techniques are applicable, using an assessment of the deviations from steadiness that can be tolerated without appreciable loss of accuracy and a quasi-steady methodology that controls flow within acceptable limits. Secondary goals are to reduce the cost and specialized nature of the necessary equipment, and to reduce the operator time and level of training required. Recent tests demonstrate these new techniques for carbonatic rock and other porous media. Numerical simulations predict the performance of the quasi-steady approach over a wide range of speeds and radii of rotation corresponding to various configurations, including centrifuges that are mass-produced for general laboratory use and the much larger ones designed for geotechnical applications. These simulations use a solution of Darcy's law in a centrifugal field to predict moisture conditions and net driving force within a sample, in order to assess the validity of these conditions for hydraulic property measurement. The tests and simulations show the improved techniques are useful for most porous rock and sedimentary media. With its simplified apparatus, capacity for larger samples, and the adaptability to various machines and operating conditions, the method expands the potential for exploring situations that are common in nature but have been the subject of few laboratory investigations, including macropore and fracture flow, other modes of preferential flow, and transient flow.
UR: http://wwwrcamnl.wr.usgs.gov/uzf/
DE: 1829 Groundwater hydrology
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting