HR: 08:15h
AN: H21L-02    [Abstracts]
TI: Air entry-based characteristic length improves permeability estimates for compacted earth materials
AU: * ASSOULINE, S
EM: vwshmuel@agri.gov.il
AF: Department of Environmental Physics and Irrigation, Institute of Soil, Water and Environmental Sciences, Volcani Center, A.R.O., P.O.B. 6, Bet Dagan, 50250, Israel
AU: OR, D
EM: dani.or@epfl.ch
AF: School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Federale de Lausanne (EPFL), ENAC/LASEP, Batiment GR 2 (room 399), Lausanne, 1015, Switzerland
AB: The permeability, k, of porous media is required for quantifying flow and transport processes in hydrology, civil, agriculture and petroleum engineering and is often estimated from medium porosity and additional constraints. Changes in porosity of earth materials due to compaction by anthropogenic activities or overburden result in a reduction in mean pore sizes and a decrease of k. Permeability is often expressed as proportional to a characteristic length squared and inversely proportional to a porosity factor, pore shape, and tortuosity of the material. Various characteristic lengths for the porous medium were proposed such as the hydraulic radius of Kozeny-Carman, or limiting pore size derived from critical path analysis. We introduce a characteristic length related to the air entry value compatible with Aissen formula that accommodates complex pore shapes. The proposed model includes a geometrical (tortuosity) factor and links relative changes in porosity to concurrent changes in k. The model was evaluated for three different groups of natural porous media: sands, sandstones with different cementing agents, and unconsolidated soils. For clay-free sands and unconsolidated soils, the model provides reasonable predictions for the entire range of porosities found in laboratory or field experiments. However, for sandstones with cementing agents, the model is valid up to a critical porosity where pore structure seems to collapse and k reduces drastically. The geometrical factor for soils was influenced by silt-to-clay ratio, while for granular media, it was correlated with mean grain diameter. The model offers improvement in predicting k and provides a means for incorporating critical pore size (air entry) information in addition to porosity.
DE: 1816 Estimation and forecasting
DE: 1847 Modeling
DE: 1859 Rocks: physical properties
DE: 1865 Soils (0486)
SC: Hydrology [H]
MN: 2007 Fall Meeting