Effect of Pore-Water Surface Tension on Tensile Strength of Unsaturated Sand

A custom-built direct tension apparatus was employed to perform direct tension tests on unsaturated silica sand specimens at different saturations levels and packing dry densities. Attempt was made to understand the effect of surface tension of pore-liquid. It was found that the tensile strength decreases, as the surface tension of the pore-liquid decreases. However, tensile strength does not decrease as a simple multiple of ratio of surface tension of pore-liquid. The experimental results were also compared with the predicted results from two theoretical tensile strength models. Results predicted using the micro-mechanical model agreed well with the experimental results, but only for specimens containing distilled water within the pendular regime. On the other hand, the macro-mechanical model followed the experimental trend across pendular and funicular regimes for specimens containing distilled water reasonably well. However, at reduced surface tension of pore-liquid, both models significantly under-predicted the experimental results