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 measurementprocedure for obtaining soil water content (swc), which relies on the chemical reaction ofthe calcium carbide reagent with water in soil pores. currently, the method is limited to soilsamples 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 dierent soil types containingparticles no larger than no. 4 sieve size. the water content of soil specimens with varyingwetness was measured using both conventional oven-drying and ccgp methods. the errordistribution analysis indicated that the ccgp method, as used in this study, estimates theswc for all soil types with a mean absolute discrepancy of around 0.3% and 0.2%, withgeneral and soil specic calibrations, respectively. it was found that the ccgp method isreliable for swc determination of small specimens up to 20% of swc if the manufacturer'sinstructions are followed.