Reliability of soil water content measurements by the calcium carbide gas pressure method for small specimens

The Calcium Carbide Gas Pressure (CCGP) method is a rapid measurement procedure for obtaining Soil Water Content (SWC), which relies on the chemical reaction of the calcium carbide reagent with water in soil pores. Currently, the method is limited to soil samples of 20 g or larger. However, test equipment for much smaller sample sizes does exist, and there is a need for quantifying the reliability of SWC measurements of small samples. The research involved a total of 232 tests carried out on 22 different soil types containing particles no larger than No. 4 sieve size. The water content of soil specimens with varying wetness was measured using both conventional oven-drying and CCGP methods. The error distribution analysis indicated that the CCGP method, as used in this study, estimates the SWC for all soil types with a mean absolute discrepancy of around 0.3% and 0.2%, with general and soil specific calibrations, respectively. It was found that the CCGP method is reliable for SWC determination of small specimens up to 20% of SWC if the manufacturer's instructions are followed. (C) 2014 Sharif University of Technology. All rights reserved.