Unsaturated shear strength of soil with bimodal soil-water characteristic curve

Many research works have been carried out to develop equations for shear strength of unsaturated soil. However, most of the equations are limited to soils with unimodal soil-water characteristic curves (SWCC). The objective of this study is to propose an equation for estimating the unsaturated shear strength of soils with bimodal SWCCs. Several series of unsaturated consolidated drained triaxial tests were carried out on statically compacted sand–kaolin specimens to evaluate the proposed equation. The experimental results indicated that the ϕ b angle of the soil with bimodal SWCC at suctions between the first air-entry value (AEV1) and the second air-entry value (AEV2) was less than the ϕ b angle at suctions below AEV1. However, the relationships between shear strength and suction at suctions between AEV1 and AEV2 were still linear. At suctions beyond AEV2, the ϕ b angle of the soil with bimodal SWCC started to decrease non-linearly. The evaluation results showed that the estimated bimodal shear strength using the proposed equation in this study had good agreement with the shear strength data from the experimental works.