NOTE Estimation of unsaturated hydraulic conductivity using soil suction measurements obtained by an insertion tensiometer D.N. Singh and Sneha J. Kuriyan Abstract: To estimate the unsaturated soil hydraulic conductivity of a silty soil, an insertion tensiometer has been used for measuring its suction corresponding to different water contents. These suction values have been used for developing the soil-water characteristic curve (SWCC). The obtained SWCC has been compared with the trends predicted by vari- ous fits available in the literature. Further, with the help of the obtained SWCC, the unsaturated soil hydraulic conduc- tivity has been estimated. The study demonstrates the usefulness of insertion tensiometers for measuring soil suction and for estimating its hydraulic conductivity. Key words: silty soil, suction, insertion tensiometer, soil-water characteristic curve, unsaturated soil hydraulic conductivity. Résumé : Afin d’évaluer la conductivité hydraulique non saturée d’un sol limoneux, un tensiomètre inséré dans le sol a été utilisé pour mesurer la succion correspondant à différentes teneurs en eau. Ces valeurs de succion ont été utilisées pour développer la courbe caractéristique sol-eau (SWCC). La courbe SWCC a été comparée avec les tendances prédi- tes par différentes concordances disponibles dans la littérature. De plus, au moyen de la courbe SWCC obtenue, on a estimé la conductivité hydraulique du sol non saturé. L’étude démontre l’utilité des tensiomètres insérés dans le sol pour mesurer la succion du sol et pour estimer sa conductivité hydraulique. Mots clés : sol limoneux, succion, tensiomètre inséré dans le sol, courbe caractéristique sol-eau, conductivité hydraulique du sol non saturé. [Traduit par la Rédaction] Singh and Kuriyan 483 Introduction Contamination of ground water regime and subsurface soils is one of the major problems that have arisen as a result of rapid industrialization. The spread of contaminants in the unsaturated soil strata, mainly close to the ground surface and lying above the water table, depends on its hydraulic conductivity. As such, estimation of unsaturated soil hydrau- lic conductivity becomes very important (Mualem 1986). In this connection, researchers have mostly conducted column tests to study flow through unsaturated soils. They have re- sorted to both steady state (Uno et al. 1995; Fleureau and Taibi 1995) as well as transient methods (Youngs 1964). These studies reveal that most field and laboratory methods of determining the unsaturated soil hydraulic conductivity are either time consuming, tedious, or have other logistical difficulties (Stephens 1996). At the same time, empirical relations have been developed by a number of researchers (Rawls and Brakensiek 1985; Mualem 1986; Rawls et al. 1991, 1992) to determine soil hydraulic conductivity, assuming that the soil follows a partic- ular model or relationship between the hydraulic conductivity and the pressure-head (Gardner 1958; Brooks and Corey 1964; Leong and Rahardjo 1997a, 1997b) and (or) water content (Averyanov 1950; Burdine 1953; Mualem 1976; Klute and Dirksen 1986, Leij et al. 1997). However, the drawback of these relations is that, each one of them is soil specific and based on a limited amount of data. As such, the relation appli- cable to one type of soil cannot be applied directly to another soil without characterizing it (Zaradny 1993). In such a situation, estimation procedures are generally resorted to wherein the soil hydraulic conductivity can be estimated from the moisture retention curves or the soil-water characteristic curves (SWCCs) (Fredlund and Xing 1994; Fredlund et al. 1994). However, the efficiency of these procedures depends on the accuracy with which the suction versus volumetric water content relationship is deter- mined. Although, many sophisticated suction measurement devices (Gourley and Schreiner 1995; Lee and Wray 1995; Woodburn and Lucas 1995) have been used for measuring Can. Geotech. J. 40: 476–483 (2003) doi: 10.1139/T02-112 © 2003 NRC Canada 476 Received 7 March 2001. Accepted 2 October 2002. Published on the NRC Research Press Web site at http://cgj.nrc.ca on 1 April 2003. D.N. Singh 1 and S.J. Kuriyan. Department of Civil Engineering, Geotechnical Engineering Division, Indian Institute of Technology Bombay, Powai, Mumbai – 400 076, India. 1 Corresponding author (e-mail: dns@civil.iitb.ac.in).