University of California Pavement Research Center

One of the important components of a flexible pavement structure are granular material layers. The unsaturated granular pavement materials (UGPMs) in these layers influence stresses and strains throughout the pavement structure, and can have a large effect on asphalt concrete fatigue and pavement rutting, which are two of the primary failure mechanisms for flexible pavements. The behavior of UGPMs is highly dependent on water content, but this effect has been traditionally difficult to quantify using either empirical or mechanistic methods.This report presents a mechanistic framework for normalizing the behavior of UGPMs within the range of water contents, densities, and stress states likely to be encountered under field conditions. Both soil suction and generated pore pressures are calculated and compared to applied confinement under typical field loading conditions. The framework utilizes a new soil suction model that has three density-independent parameters, and can be determined using conventional triaxial equipment that is available in many pavement engineering laboratories. The suction model can be included with an effective stress constitutive model to determine the response of UGPMs under different loading conditions.