Predicting unsaturated hydraulic conductivity of coarse unconsolidated sediment based on grain size
- Florida State Univ., Tallahassee, FL (United States). Dept. of Geology
The unsaturated hydraulic conductivity of a coarse sediment varies with capillary pressure, which in turn depends on the complex arrangement of pores within the sediment. Present theories indicate that unsaturated conductivity is systematically related to the distribution of pore sizes. In particular, the work of Brooks and Corey demonstrates that unsaturated conductivity decreases with decreasing mean pore size, and decreases with increasing variance for given mean. Using dimensional arguments, the authors have inferred that a similar relation between unsaturated conductivity and the distribution of grain sizes must exist. In particular, it is shown that the Brooks-Corey theory and the Gardner theory (based on soil texture) contain essentially the same information regarding pore sizes. The use of grain size is easier, and therefore more appealing, than pore size for developing prediction models. To test their dimensional arguments, several grain mixtures were constructed so that conditions of geometric similitude were satisfied. A constant-head permeameter that induces unsaturated flow within samples was used to obtain values of conductivity at varying pressure heads. Data indicate that unsaturated conductivity systematically increases with mean grain size and decreases with increasing variance, consistent with their hypothesis. Further, the slope of the relative conductivity characteristic increases systematically with decreasing mean, and increasing variance, of grain sizes. This relation yielded favorable fits with observed conductivities for undisturbed field samples and glass beads. The data further corroborate their dimensional argument in that bubbling pressure is inversely proportional to mean grain diameter for geometrically similar mixtures.
- OSTI ID:
- 5808958
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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