Comparison of Measured and Predicted Suction Stress in Partially Saturated Compacted Mixtures of Sand and Clay

Abstract

We conducted conventional triaxial and uniaxial tensile tests using partially saturated samples of an artiicial compacted mixture of kaolin and sand. Test results were analyzed by applying the effective stress principle in partially saturated soils. The results showed that suction stresses derived by triaxial and tensile tests were consistent at saturations >0.1, while the prediction of suction stress from the drying and wetting soil water characteristic curves of the mixture failed. Experimental results indicated that soil structure effects result in differences in upscaling the microscopic interaction effects to macroscopic strength at different suction levels. These soil structure effects seem to differ for shear strength and tensile strength..Abbreviations: SWCC, soil water characteristic curve.To date there is an ongoing discussion about how to describe the efect of soil-water interaction (in terms of suction) when dealing with the mechanical behavior, especially the shear strength, of partially saturated soils (e.g., Nuth and Laloui, 2008;Gens, 2010). Generally, two stress state variables, the net stress (mechanical stress) and the suction (suction stress) are considered in constitutive partially saturated soil modeling (Sheng 2011). he approaches difer, among other things, in treating these stress variables as independent variables (Fredlund et al., 1996;Sheng et al., 2008) or lumping both components to a single stress variable (Lu and Likos, 2006;Rojas et al., 2008;Lu et al., 2010). he latter approach has the fundamental advantage that classical soil mechanic principles can be applied to partially saturated soils. In addition, if the friction angle of the soil is independent of suction, all shear strength descriptions can be formulated either in the form of the independent or single variable approach. he growing number of laboratory tests indicates that the efective stress concept is suficient to describe macroscopic efects from soil-water interaction when dealing with shear-strength-related problems (Geiser et al.a unique closed-form equation to predict suction stress is still missing.We compared "measured" (derived by experimental data) and predicted (based on theory) shear strength of a partially saturated artiicial sand-clay mixture using the efective stress concept proposed by Lu and Likos (2006) and the closed-form equation for this stress from Lu et al. (2010). Conventional triaxial tests and uniaxial tensile strength tests were performed. he tests allowed us to measure failure under tensile to high compression stress conditions for air-dry to saturated conditions. Measured soil water characteristic curves (SWCCs) were used to predict suction stress and therefore the shear strength of the partially saturated soil.We irst introduce the efective stress concept and the methods used to derive and predict stresses resulting from the interaction of soil and water. his is not intended to be a Triaxial and uniaxial tensile tests were conducted using an artiicial mixture of kaolin and sand. Test results are...

Principle of Effective Stress in Variably Saturated Porous Media

“…The validity of the SSCC‐based effective stress principle representation is further demonstrated in “Comparison of Measured and Predicted Suction Stress in Partially Saturated Compacted Mixtures of Sand and Clay,” by Pourzargar et al (2014) through unsaturated triaxial shear strength tests and unsaturated tensile strength tests for kaolinite–sand mixtures. The work shows that the closed form equation for the SSCC proposed by Lu et al (2010) can represent both shear strength and tensile strength behavior for soils with non‐monotonic behavior in the SSCC.…”