Microstructural interpretation of effective stress equations for unsaturated sands

Abstract

Abstract It was fairly accepted to interpret soil behaviour at the microstructural level by utilising the effective degree of saturation instead of the total degree of saturation in the effective stress equation for unsaturated fine-grained soils. However, this interpretation for pure sands was under-represented in the literature. On the basis of shear strength evolution with suction, this paper reports a series of experimental tests to evaluate the use of the soil microstructural interpretation for fine sands. The tests comprised direct shear and unconfined-compression tests at different suction profiles. The analysis of the experimental test results suggested that the contribution of the effective degree of saturation was trivial and was almost equal to the total degree of saturation, therefore, shear strength evolution, owing to the suction effect, can be related to the single stress variable, Bishop’s equation. In addition, it was hypothesised that the shear strength evolution was attributed to the soil fabric changes.

Keywords

• Shear resistance
• Microstructural analysis
• Effective stress
• Effective degree of saturation