The Suction Pressure, Yield Strength and Effective Stress of Partially Saturated Unbound Granular Pavement Layers

The predominant mode of distress for unbound pavement layers is the permanent deformation of the layer either through gradual deformation or rapid shear failure of the layer. Several researchers have related both these forms of permanent deformation to the ratio of the imposed stress over the shear strength of the material. Conventionally, the shear strength of the material was characterised with the Mohr-Coulomb shear strength parameters. This paper further develops a recent yield strength model that includes an approximation of the suction pressure in the formulation of the model. The suction pressure approximation is extended to include the effect of density on the suction pressure. The calibration of the suction pressure approximation and yield strength model using conventional tri-axial test results are presented for a sand and calcrete mixture. The soil-water characteristic curve derived from the suction pressure approximations is validated using actual matric suction measurements. The effects of suction pressure and effective stress on pavement design calculations are also illustrated.