Comparison of four methods for measuring total suction

This study assessed four methods for measuring soil total suction in laboratory: the noncontact filter paper method, the psychrometer technique, the relative humidity ( RH) sensor, and the chilled- mirror hygrometer technique. Our aim in this study was to compare the four total suction measurement techniques, especially the psychrometer method and the RH sensor, which may be used for field total suction measurements. While field application of the sensors is the eventual concern, no field measurements were performed in the study. Assessment was made using two bentonite - sand mixtures, which can be used as clay liner for landfills. A discussion of factors influencing measurement accuracy is also provided. The chilled- mirror hygrometer technique appears to give the most accurate results, and therefore may used as a benchmark for assessing the accuracy of the three other methods. For the bentonite - sand mixture used in this study, the total suction measured using the noncontact filter paper technique represents values at a quasi- equilibrium state after redistribution of water in the specimen, instead of the total suction at as- compacted state. The RH sensor provided a faster response than the psychrometer technique However, the RH sensor exhibited a systematic error in the small suction range.