CORRELATION OF DESICCATION FRACTURE CHARACTERISTICS TO MOISTURE CONTENTS AND GRAIN SIZE DISTRIBUTIONS IN CENTRAL TEXAS SMECTITE CLAY SOILS

Soils and sediments with high smectite clay contents are generally treated as barriers to infiltration and subsurface fluid flow. However, these clays have a high shrink-swell potential and are subject to extensive cracking when they dehydrate. These desiccation fractures can act as conduits for infiltration and can increase the potential risk of contamination of potable water supplies from surface releases. An understanding of infiltration and flow through high-smectite clay soils requires a quantitative understanding of the development of these fractures and their relationship to properties of the soil, such as moisture content and grain-size distribution.

Desiccation fracture networks in clay soils at ten sites on a central Texas property were measured and monitored between March 2004 and September 2004. Samples from each site were analyzed for grain-size distributions. Digital photos of exposed fractures at each site were taken approximately once per week. The fracture networks in the photos were manually traced using a standard vector graphics program (Macromedia Freehand 10). Each digitized fracture network was then exported into a spreadsheet file using the Encapsulated Post Script file format, and the networks were analyzed to determine fracture densities, anisotropy, and aperture distributions. Field measurements of fracture depth were also taken and correlated to fracture apertures. Soil gravimetric moisture contents were also measured at each site during each fracture measurement event. These moisture contents were then correlated to the fracture measurements. These correlations are used to quantify the mathematical relationship between moisture content and fracture development in shrink-swell clay soils.