Identifying Shallow Expansive Clays Prior To Site Development Using Capacitively Coupled Resist

Capacitively coupled resistivity (CCR) has proven useful for mapping shallow soil conditions<br>over large sites prior to development. Because the CCR unit can be towed at a rate 1 to 5 kilometers per<br>hour, it allows large sites to be surveyed quickly. The availability of a multi-channel CCR instrument<br>allows resistivity profiles to be generated from a single pass along a transect line. The CCR profiles<br>provide useful information to the geotechnical engineers evaluating the site, in particular:<br>1. The ability to delineate areas with shallow expansive clays, which are a concern for shrinking<br>and swelling beneath a foundation; and<br>2. The ability to delineate areas of deeper surficial sands, which are suitable for fill.<br>As part of a recent study, resistivity values were compared to the plasticity index and grain-size<br>analyses of the soils. The CCR data were then used to delineate areas of high plasticity clay, low<br>plasticity clay and clean sands.