Abstract
The undrained strength su of saturated soil is related to the void ratio or equivalently to Hvorslev's equivalent pressure. In the transition zone of unsaturation the pore air pressure may be assumed atmospheric, airphase being continuous.
The effective stress parameter χ can be adopted, and if the critical state strength is relevant a simple linear strength envelope is applicable. From known water content and void ratio the horizontal shift of the failure envelope by the suction stress may be computed, and the resulting capillary cohesion can be used in stability analyses using the conventional solutions for saturated soils.
Laboratory tests confirmed the applicability of the simple concept for compacted silty clay for water contents at or above optimum. The texture of the soil compacted dry of optimum seemed to influence the properties strongly, and the simple concept was not found applicable.