Effect of surface tension on tensile strength of moist uniform fine sand

Rashid Bashir, Prateek Jindal, Jitendra S. Sharma

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Soil Mechanics

ABSTRACT: surface tension on tensile strength of moist uniform fine sand Rashid Bashir, Prateek Jindal & Jitendra S. Sharma Department of Civil Engineering Œ York University, Toronto, ON, Canada ABSTRACT In routine geotechnical engineering practice, it is generally accepted that for coarse-grained materials, such as sands, the tensile strength is negligible. This paper describes a research attempt to understand the role of surface tension of pore water on the tensile strength of a moist sand. The tensile strength measurements were made in a custom-built soil tension device. Surface tension of pore water was reduced by introducing a surface active solute in various concentrations. The results indicate that the tensile strength is a function of concentration dependent surface tension. This observation also highlights the possible effects on soil strength properties in applications where surfactants are introduced as part of remediation strategy or waste water containing large amount of surfactants is used as a water management option. RÉSUMÉ Dans la pratique de l'ingénierie géotechnique, il est généralement admis que la résistance à la traction pour les matériaux à gros grains, comme les sables, est négligeable. Cet article décrit une méthode de recherche pour comprendre le rôle de la tension de surface de l'eau interstitielle sur la résistance à la traction d'un sable humide. Les mesures de résistance à la traction ont été faites dans un dispositif de tension du sol sur mesure. La tension superficielle de l'eau a été réduite par l'introduction d'un soluté à diverses concentrations. Les résultats indiquent que la résistance à la traction est une fonction de la tension de surface dépendant de la concentration. Cette observation aussi souligne les effets possibles sur les propriétés de résistance du sol dans les applications où les tensioactifs sont introduits dans le cadre de la stratégie d'assainissement, ou d'eaux usées qui contient beaucoup d'agents tensioactifs sont utilisé comme une option de gestion de l'eau. 1 INTRODUCTION In routine geotechnical engineering practice, it is generally accepted that that coarse-grained materials, such as sands, exhibit only shear strength with negligible tensile strength. There is significant evidence that inter-particle forces arising from capillary and other pore-scale force mechanisms increase both the shear and tensile strength of soils (Fredlund et al. 1978; Kim 2001; Goulding 2006,). In a granular media, the tensile strength is a result of various inter-particle physico-chemical forces such as van der Waal's attraction, capillary stress due to negative pore water pressure, surface tension of the wetting fluid, and electric double layer. (Lu and Likos 2004; Lu et al. 2007; Kim and Sture 2008); however, for most practical design purposes, the tensile strength of the sands is not taken into account due to lack or experimental data and common perception that tensile strength is insignificant in granular materials (Kim and Hwang 2003). A variety of problems, such as shallow slope stability, lateral earth pressure, fill compaction, and shallow foundations, present situations where the soil is in an unsaturated state and its tensile strength could be of significance. There have been a few attempts to quantify the tensile strengths of moist sands (Bishop and Garga 1969; Perkins 1991; Kim 2001; Goulding 2006; Kim and Sture 2008). Major advances have been made in quantifying the capillary mechanisms in unsaturated granular materials (Rumpf 1961; Schubert 1975; Pierrat and Caram 1997; Kim 2001; Lu et al. 2007). It has been known for decades that most organic compounds decrease the surface tension of water in relation to their aqueous concentration (Smith 1995; Henry et al. 2001). Laplace equation of capillarity (Bear 1972) relates soil water pressure (negative capillary pressure or matric suction) to surface tension as: ==+ [1] where is the pressure head, is the matric suction, is the airŒwater surface tension, is the solution density, g is the gravitational acceleration, and r1 and r2 are the principal axes of curvature of the airŒwater interface. The above equation indicates that the matric suction and surface tension are proportional to each other and any reduction in surface tension will result in an equivalent reduction in the matric suction. A reduction in surface tension can additionally affect capillarity by modifying the contact angle. The apparent contact angle () can be written as the function of the affinity of different fluids for each other and for solid surface in the following form: = [2] where with L,G, and S indicate liquid, gas, and solid, respectively, and is the interfacial surface tension. For a curved interface, within a pore of equivalent spherical radius, the following equation relates the

RÉSUMÉ: t of surface tension on tensile strength of moist uniform fine sand Rashid Bashir, Prateek Jindal & Jitendra S. Sharma Department of Civil Engineering Œ York University, Toronto, ON, Canada ABSTRACT In routine geotechnical engineering practice, it is generally accepted that for coarse-grained materials, such as sands, the tensile strength is negligible. This paper describes a research attempt to understand the role of surface tension of pore water on the tensile strength of a moist sand. The tensile strength measurements were made in a

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Rashid Bashir; Prateek Jindal; Jitendra S. Sharma (2014) Effect of surface tension on tensile strength of moist uniform fine sand in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper323,author = Rashid Bashir; Prateek Jindal; Jitendra S. Sharma,title = Effect of surface tension on tensile strength of moist uniform fine sand,year = 2014}