HR: 1340h
AN: H33A-1369    [Abstracts]
TI: An Air-water Interfacial Area Based Variable Tortuosity Model for Unsaturated Sands
AU: * Khaleel, R
EM: raziuddin_khaleel@rl.gov
AF: Fluor Government Group, P.O. Box 1050, Richland, WA 99352 United States
AU: Saripalli, P
EM: prasad.saripalli@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99354 United States
AB: A new variable tortuosity definition is introduced that is based on the immiscible fluid (air-water) interfacial area. Unsaturated media tortuosity (τ_a) is defined as the ratio of a_aw to a_aw,o where a_aw is the estimated air-water interfacial area in a real unsaturated medium (i.e., a soil sample), and a_aw,o is the same variable for the corresponding, idealized capillary bundle. We establish equivalence between the real and the idealized media by letting the laboratory-measured retention curve calculate the distribution of capillary tubes, thereby resulting in an identical pore-size distribution but a new retention curve for the idealized medium. The air-water interfacial area for both real and idealized media is directly proportional to the area under their respective retention curves. With τ being the saturated tortuosity, we relate the variable tortuosity ratio (ττ_a) to the S_e^ε term in Mualem's (ε=0.5) and Burdine's (ε=2) pore-size distribution models. Thus, instead of using tortuosity and/or pore connectivity formulations that have empirical exponents of either 0.5 or 2, the new model depends on variable interfacial area for varying saturation and soil texture, as reflected in the measured retention data. We tested the new definition of tortuosity for 22 repacked Hanford sediments that are comprised of mostly coarse and fine sands but some also contain a sizeable fraction (as high as 27%) of fines (silt and clay). Replacing the S_e² term in van Genuchten-Mualem (VGM) model by the new interfacial area based variable tortuosity ratio, and still using saturated conductivity and retention parameters, as used in the conventional approach, we obtain interfacial area based K(θ) predictions that are nearly identical to the conventional VGM model predictions. We also compare the interfacial area based K(θ) predictions with the standard Brooks-Corey-Burdine (BCB) model predictions. Compared to the VGM model predictions, interfacial area based BCB K(θ) predictions appear to be less biased relative to the measured K for the coarse-textured samples.
DE: 1838 Infiltration
DE: 1866 Soil moisture
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005