Effect of Ambient Temperature on the Calibration of Thermal Conductivity Suction Sensors

R. Bashir, J.J. Stone, D.G. Fredlund

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Behaviour of Unsaturated Soils

ABSTRACT: Soil suction is one of the stress state variables for describing unsaturated soil behavior. Unsaturated soil properties are a function of soil suction and as a consequence, the measurement of soil suction becomes extremely important to the implementation of unsaturated soil mechanics into geotechnical engineering practice. Thermal conductivity (TC) suction sensors can be used for the in situ and laboratory measurement of soil suction. The indirect measurement of soil suction uses the thermal conductivity measurement on a specially designed porous ceramic to provide a measure of soil suction. Soil suction values can be obtained by calibrating the sensors in the laboratory prior to installation in the field. A question has arisen regarding the sensitivity of the calibration curves to the ambient temperature. The present research study focuses on determining a calibration procedure that compensates for ambient temperature. Experimental calibration studies were undertaken at the Golder Unsaturated Soils Laboratory in Saskatoon, using a new custom built calibration cell placed in a controlled temperature environment. Three sets of calibration curves were measured on the TC suction sensors corresponding to three different but constant temperatures. The temperatures selected for the calibration study were 10oC, 21oC and 35oC. The calibrations consisted of measuring the thermal conductivities of the sensors at 10 different applied suctions ranging from completely saturated to completely dry states. The results of the experimental measurements were analyzed to provide an improved calibration procedure that takes into account the affect of ambient temperature.

RÉSUMÉ: La succion des sols est l'une des variables de l'état de stress servant à décrire le comportement des sols non saturés. Les propriétés des sols non saturés sont une des fonctions de la succion du sol. Par conséquent, la mesure de la de la géotechnique. Les capteurs de la succion de la conductivité thermique (CT) laboratoire afin de mesurer la succion du sol. La mesure indirecte de la succion du sol utilise la mesure de la uccion du sol. Les valeurs de succion du sol peuvent être obtenues en effectuant un étalonnage des capteurs en laboratoire avant l'installation sur le terrain. Une interrogation a surgi concernant la sensibilité des courbes de calibration de la température ambiante. de Golder, Saskatoon, en utilisant une nouvelle cellule de mesure d'étalonnage crée sur mesure et placé dans un environnement à température contrôlée. Trois séries de courbes d'étalonnage ont été mesurées sur les capteurs de succion TC correspondants à trois températures différentes, mais constantes. Les températures sélectionnées pour l'étude d'étalonnage ont été 10°C, 21°C, et 35°C. Les étalonnages consistaient à mesurer la conductivité thermique des capteurs à 10 différentes succions appliquées, allant de complètement saturé à complètement sec. Les résultats des mesures expérimentales ont été analysés afin de fournir une procédure de calibration améliorée qui tient compte de l'effet de la température ambiante.

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Cite this article:
R. Bashir; J.J. Stone; D.G. Fredlund (2011) Effect of Ambient Temperature on the Calibration of Thermal Conductivity Suction Sensors in GEO2011. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GEO11Paper618,author = R. Bashir; J.J. Stone; D.G. Fredlund ,title = Effect of Ambient Temperature on the Calibration of Thermal Conductivity Suction Sensors,year = 2011}