Strain response and performance of subgrades and flexible pavements under various loading conditions

Specific fundamental loading parameters (load magnitude and number of repetitions, tire inflation pressure, and basic tire type) that influence the behavior of thin-surfaced granular pavements were examined. The pavement response and performance measurements included continuous surface deflection basins, longitudinal and transverse profiles, and vertical strains in the granular layers and subgrade. The first pavement trial considered only the elastic response of a thin-surfaced, unbound granular pavement over a weak subgrade, to varying wheel loads, tire inflation pressures, and two basic tire types (bias and radial ply). The axle load had the greatest effect on pavement response and the tire type had no apparent effect, but increases in the tire pressure resulted in slight decreases in the magnitude of the vertical compressive strain in the subgrade and unbound granular cover. Two subsequent pavements were tested to study the relationship between elastic response at different cumulative loadings and the structural capacity of each pavement. The magnitudes of the resilient strains measured are substantially greater than the levels predicted by the models on which current flexible pavement design procedures are based for the same number of loading repetitions to failure. Subgrade strain models for thin-surfaced unbound granular pavements are evaluated. The pavement construction, loading routine, analysis, and results are discussed.