Calibrations of a high-suction tensiometer

Abstract

Citation for published item:vouren oD F hF xF nd qllipoliD hF nd ollD hF qF nd eugrdeD gF iF nd ivnsD pF hF nd wederoD qF wF @PHHVA 9glirtions of high sution tensiometerF9D q¡ eotehniqueFD SV @VAF ppF TSWETTVF Further information on publisher's website: httpXGGdxFdoiForgGIHFITVHGgeotFPHHVFSVFVFTSW Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. , et al. (2008). Géotechnique 58, No. 8, 659-668 [doi: 10.1680/geot.2008 659Calibrations of a high-suction tensiometerHigh-suction tensiometers are able to measure suctions up to 2 MPa. Direct calibration at such high suctions requires the imposition of negative water pressures, which are difficult to achieve using facilities commonly available in soil mechanics laboratories. For this reason, tensiometers are usually calibrated in the positive pressure range, and such calibration is subsequently extrapolated to negative pressures. This paper examines different experimental techniques to assess the accuracy of such extrapolation. Any error in the calibration process would be directly reflected in the measured values of suction, and might be particularly significant (in relative terms) for the measurement of low suctions. In addition, the results of this study show that calibration in the positive range is affected both by the physical configuration of the tensiometer during calibration and by aspects of its design. The paper concludes that linear extrapolation of the calibration from the positive to the negative range is sufficiently accurate provided that calibration is done under conditions that closely match the conditions in which the tensiometer will be used. Owing to structural differences between tensiometers, and also to suctioninduced 'calibration hysteresis', at least one check on the accuracy of the extrapolated calibration equation over a range of negative pressure should be performed, even if at low values of suction.

Advances in suction measurements using high suction tensiometers

“…The cavitation limit of the device imposes an upper limit on the suction that can be measured. The maximum suctions that have been directly measured by high suction tensiometers are those reported by Tarantino and Mongiovì (2001) who achieved 2.6 MPa and Lourenço et al (2008) who achieved 2.1 MPa (Figure 2). As tensiometers measure pore water pressure directly, errors related to indirect calibration curves are avoided, such as those used for electrical or thermal conductivity sensors or for filter paper techniques.…”

“…Ridley and Burland (1993), Guan and Fredlund (1997) and Lourenço et al, (2008) have used the axis translation method and the isotropic unloading method to investigate this. Both techniques impose a known suction on an instrumented soil sample.…”

A new technique for deep in situ measurements of soil water retention behaviour

“…less than −100 kPa). Since the pioneering work by Ridley and Burland (1996), know-how regarding high-capacity tensiometers (HTCs), capable of measuring in excess of 1 MPa, has advanced considerably (Lourenço et al, 2008), but only recently have designs specific to field applications been developed (e.g. Toll et al, 2011).…”

Building the UPPA high capacity tensiometer

“…This HCT, whose design is shown in Figure 1, was able to measure values of suction greater than 1500 kPa. Since then, other HCTs with similar design have emerged, such as those described in [2][3][4][5][6][7][8][9] among others. Ridley and Burland in 1993 [1].…”