High Capacity Tensiometers: performance and behaviours

High capacity tensiometers (HCT) allow the direct measurement of soil matric suction, and their major limitation is the occurrence of cavitation. In this paper HCT designs using different ceramic filters with varied air entry values (AEV), varied reservoir sizes, and different pressure transducers are assessed as to determine the impact that each component may have in the HCT performance. Moreover, the effectiveness of first saturation and resaturation processes is discussed in relation to the time required to prepare/recover HCTs. The results obtained with the different designs show that the measuring range is directly linked to the AEV of the ceramic filter and that the choice of materials used for the various components may affect the reliability of measurements in field installations if the thermal performance is not accounted for in the calibration procedure. The use of a 1hr high vacuum pre-stage followed by overnight water pressurisation at pressures equal or above the AEV of the ceramic filter was found to be the quickest process to fully saturate an HCT for the first time. While resaturation time for an HCT can be reduced to as little as a few minutes if the HCT is resaturated immediately after cavitation has occurred.