Bi-linear strength envelope of coarse- and fine-grained unsaturated soils with bimodal water-retention curve.

Many engineering practices are carried out within the unsaturated soil. Soil-water retention curves (SWRCs) of many soils exhibit bimodal characteristics that significantly affect strength behavior, this issue still remains unresolved. This work employs suction stress concept to examine the uniqueness of strength parameters for coarse- and fine-grained unsaturated soils with bimodal SWRCs. Capillary degree of saturation is used to upscale pore-scale suction to macroscopic suction stress. In the suction stress-shear strength plane, both coarse- and fine-grained soils display the bi-linear strength envelope, differing from unsaturated soils with unimodal SWRC. • The shear strength of unsaturated soils with bimodal water-retention curves are analyzed using suction stress concept. • The influences of soil type on the shear strength of soils with bimodal SWRC are discussed. • The unified strength criterion for soils with bimodal SWRC is manifested by a bi-linear relationship. [ABSTRACT FROM AUTHOR]