NOTE / NOTE Measurements of suction versus water content for bentonite–sand mixtures Setianto Samingan Agus, Tom Schanz, and Delwyn G. Fredlund Abstract: Compacted soils have been widely used as landfill barriers because of favorable characteristics such as low co- efficient of permeability and high swelling. Compacted bentonite–sand mixtures are normally unsaturated and therefore suction can be used as a behavioral indicator in addition to generally used factors such as water content and dry density (or void ratio). This study focused on investigating suction characteristics of bentonite–sand mixtures. Suction was meas- ured using various techniques for compacted bentonite–sand mixtures. The laboratory results were analyzed to provide an understanding of the suction concept in expansive soils. It was found that suction depends primarily on the water content and the bentonite content of the mixture, and suction in expansive soils changes with the time of hydration. Key words: suction, suction components, suction measurements, bentonite–sand mixture, compaction, bentonite water con- tent. Re ´sume ´: Les sols compacte ´s sont utilise ´s fre ´quemment comme barrie `re pour des de ´potoirs en raison de leurs caracte ´risti- ques favorables, comme leur faible coefficient de perme ´abilite ´ et de leur capacite ´ de gonflement e ´leve ´. Les me ´langes ben- tonite–sable sont normalement non sature ´s, et ainsi la succion peut servir d’indicateur du comportement, en plus des facteurs usuels comme la teneur en eau et la densite ´ se `che (ou indice des vides). Cette e ´tude vise a ` investiguer les caracte ´- ristiques de succion des me ´langes bentonite–sable, a ` partir de mesures de succion faites avec diffe ´rentes techniques. Les re ´sultats de laboratoire ont e ´te ´ analyse ´s dans le but de fournir une meilleure compre ´hension du concept de succion dans les sols expansifs. Il a e ´te ´ de ´termine ´ que la succion de ´pend principalement de la teneur en eau et du contenu en bentonite du me ´lange. L’e ´tude a aussi permis de de ´terminer que la succion dans les sols expansifs varie selon le temps d’hydra- tation. Mots-cle ´s : succion, composantes de la succion, mesures de succion, me ´lange bentonite–sable, compaction, teneur en eau de la bentonite. [Traduit par la Re ´daction] Introduction In landfill applications of compacted clay, one of the cri- teria commonly used for the performance of a landfill liner is the coefficient of permeability of the liner. The presence of clay material is therefore important. The addition of ben- tonite to granular material can change the performance of a highly permeable material and transform it to a material suitable for use as an engineered barrier for landfills. This type of mixture is often referred to as a bentonite-enhanced sand mixture with a low percentage of bentonite. Stewart et al. (1999) indicated that an addition of 10% sodium-type bentonite (dry mass basis) is sufficient to reduce the coeffi- cient of permeability of sand up to several of magnitudes. A further increase in the percentage of bentonite may not lead to a decrease in the coefficient of permeability of the mix- ture (Studds et al. 1998). For a less active bentonite such as a calcium-type bentonite, a higher percentage of bentonite, possibly with higher field compaction density, is required to achieve the same performance as a sodium-type bentonite – sand compacted mixtures. Compacted bentonite–sand mixtures are normally unsatu- rated (Fig. 1) and therefore suction can be used as a behav- ioral indicator in addition to generally used factors such as water content and dry density (or void ratio). The presence of suction in compacted bentonite–sand mixtures is often as- sociated with the collapse behavior of compacted mixtures. However, there are also correlations between suction, col- lapse behavior, and the coefficient of permeability of the mixtures. A mixture that is compacted dry of optimum to an intermediate dry density has a relatively ‘‘low’’ degree of saturation and a high suction and tends to exhibit collapse under specific overburden pressures because of its meta- Received 4 September 2007. Accepted 28 August 2009. Published on the NRC Research Press Web site at cgj.nrc.ca on 4 May 2010. S.S. Agus. Mott MacDonald Pte Ltd., Singapore. T. Schanz. 1 Laboratory of Foundation Engineering, Soil and Rock Mechanics, Faculty of Civil Engineering, Ruhr-University Bochum, Universita ¨tsstrasse 150, 44780 Bochum, Germany. D.G. Fredlund. Golder Associates Ltd., 145 – 1st Avenue N, Saskatoon, SK S7K 1W6, Canada. 1 Corresponding author (e-mail: tom.schanz@rub.de). 583 Can. Geotech. J. 47: 583–594 (2010) doi:10.1139/T09-120 Published by NRC Research Press