HR: 1330h
AN: H32A-0527    [PDF]
TI: Influence of Air Discontinuity and Wall Effects on the Measurements of Hydraulic Parameters Under Dynamic Conditions
AU: * Looms, M C
EM: mcl@geo.geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, DK-1350 Denmark
AU: Jensen, K H
EM: khj@geo.geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, DK-1350 Denmark
AU: Wildenschild, D
EM: wildend@science.oregonstate.edu
AF: Oregon State University, Department of Geosciences, 104 Wilkinson Hall, Corvallis, OR 97331-5506 United States
AU: Christensen, B S
EM: brc@er.dtu.dk
AF: Technical University of Denmark, Environment & Resources, Building 115, Kgs. Lyngby, DK-2800 Denmark
AU: Gudbjerg, J
EM: jag@er.dtu.dk
AF: Technical University of Denmark, Environment & Resources, Building 115, Kgs. Lyngby, DK-2800 Denmark
AB: Both dynamic (one-step) and semi-static (syringe pump) outflow experiments were carried out in the lab to test whether the resulting retention characteristics differed according to experiment type. Three sands of varying uniformity and coarseness were packed in a cylindrical sample holder. Compressed air was used to control the air phase pressure, while water was allowed to drain at atmospheric pressure from the outlet at the bottom of the sample. During the outflow experiments the capillary pressure was measured within the sample holder using a tensiometer connected to a pressure transducer. A medical CT-scanner was used to visualize and quantify the outflow patterns within the sand matrix during selected outflow experiments. Positive vertical shifts in capillary pressure during dynamic experiments were found in all three sand types at saturations close to porosity. The size and shape of the shifts corresponded with the dynamic effects found in previous work on the topic. Furthermore, the shifts were slightly greater in the coarsest and most uniform sand type. Numerical simulations of the one-step experiments using HYDRUS1D and T2VOC showed, however, that one of the basic assumptions when calculating the capillary pressure was most likely violated. The air phase could not be considered to be continuous at all times, and assuming this to be the case would result in positive shifts of the retention curves when running T2VOC. The results of using the CT-scanner showed the importance of achieving a homogeneous packing, since the investigated sand packing turned out to have an area at the edge of the sample holder with a higher porosity. This caused the edge to control the initial drainage. Therefore, the data collected at high saturations could not be expected to adequately describe the hydraulic properties of the inner sand. We also found that the time at which the inner sand commenced drainage coincided with a jump in capillary pressure for the resulting measured retention curve.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2003 Fall Meeting