General Model for the Uniaxial Tensile Strength Characteristic Curve of Unsaturated Soils

Characterization of tensile strength is critical to investigate the influence of desiccation and tensile cracks on the structural integrity of natural and artificial earthen structures and slopes. Although several models for the prediction of tensile strength of unsaturated soils have been proposed in the literature, critical gaps remain regarding a comprehensive model describing the tensile behavior of all soil types over a wide range of suction. This paper presents a general model for the tensile strength characteristic curve (TSCC) which establishes a relationship between the tensile strength versus water content in unsaturated soils. The proposed model is applicable to various soil types ranging from clean sands to silty and clayey soils. Tensile strength is characterized using the suction stress concept, and the TSCC model is built upon the concept that changes in tensile strength with water content (or degree of saturation) are primarily dominated by two distinct water retention mechanisms of capillarity and adsorption. Differences in the characteristics of capillary and adsorptive mechanisms and interparticle forces cause dissimilarities in the resultant TSCC in different soil types. Thus, a two-part suction stress characteristic curve (SSCC) was incorporated into the development of the TSCC to separately account for and distinguish interparticle forces and the resultant tensile strength under capillary and adsorptive mechanisms. The model was validated against laboratory-measured tensile strength reported in the literature for 10 soils, and was found to capture the tensile behavior of sandy, silty, and clayey soils well. Compared with several alternative models, the predictive accuracy of the proposed model was greater, particularly for clayey soils at low water contents (high suction). This superior performance can be attributed to properly accounting for the effect of adsorption mechanism, which is significant in clays.