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School of Engineering and Computing Sciences (ECS)

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Publication details for Dr Charles Augarde

Lourenço, S.D.N., Gallipoli, D., Toll, D.G., Augarde, C.E., Evans, F.D. & Medero, G.M. (2008). Calibrations of a high suction tensiometer. Géotechnique 58(8): 659-668.

Author(s) from Durham

Abstract

High-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 suction induced
‘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.