Reliability of Soil Water Content Measurements by Calcium Carbide Gas Pressure Method for Small Specimens

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 the water in soil pores. Currently، the method is limited to soil samples of 20 g or larger. However، test equipment for much smaller sample size does exist، and there is a need in quantifying the reliability of SWC measurements of small samples. The research involved a total of 232 tests that were carried out on 22 different soil types containing particles no larger than No. 4 sieve size. Water contents of the soil specimens with varying wetness were measured with both the conventional oven-drying and the 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 around 0. 3% and 0. 2% with general and soil specific calibrations، respectively. It was found that CCGP method is reliable for SWC determination of small specimens up to 20% of SWC if the manufacturer’s instructions are followed.