Tensile Strength of Unsaturated Soils

Abstract

Abstract A better understanding of the nature of tensile failure in unsaturated soils is important if adequate theories explaining the behavior of soils under tillage or during processes such as frost heaving are to be developed. In this paper, the problem of tensile failure of uncemented soils is formulated by combining Aitchison's extension of the classic Haines‐Fisher model of capillary cohesion with Griffith's theory of the fracture of cracked elastic solids. Results suggest that once air intrusion has initiated desaturation, the maximum tensile strength which can be expected is about half the gauge pressure of the pore water. Effects of grain size on tensile strengths of moist soils are actually manifested through their effects on drying characteristic curves as demonstrated by similitude analysis. A parameter, χ, used to estimate tensil strength as a function of pore water pressure, is a function of the degree of pore saturation hardly influenced by the actual shapes of the drying characteristic curves. Results are presumably applicable to various analogues, including the initiation of ice‐filled cracks (ice‐lenses) in air‐free soils during the process of frost heaving.