Application of a dew point method to obtain the soil water characteristic

The dew point method, which determines suction by measuring sample temperature and dew point temperature of air equilibrated with the sample, provides a quick and accurate method for measuring suction in the range 1 to 400 MPa (pF 4 to pF 6.6). We present a procedure, using the dew point method, to prepare samples in the relevant suction range, measure suction and water content, and obtain an equation describing the soil water characteristic (SWC). Characteristics for four soil samples ranging in texture from sand to bentonite are presented. All show a linear relationship when water content is plotted vs. logarithm of suction. The slope of the characteristic is easily obtained for use in expansive soil identification.