The progressive accumulation of secondary deformation, occurring incrementally under lowamplitude, high-cycle loading in soils, can lead to significant displacement of foundations. This study has developed a novel phenomenological model to describe the shakedown accumulation behavior of secondary deformation in granular soils subjected to low-amplitude, high-cycle loading. Firstly, gradual densification of granular packing yields an average volume strain that obeys a logarithmic law as the cyclic loading persists. A log-hyperbolic function, constrained by a limit, is reasonable, considering that the strain will reach a steady state of finite value as the cycle number approaches infinity. Secondly, cyclic loadings with average stress induce the accumulation of strain in the direction of average stress as the cycle number increases. This has been incorporated into the well-known modified Cam-clay model. Lastly, the proposed model has been calibrated using data obtained from undrained and drained cyclic triaxial tests conducted on uniformly fine-grained sands. The results suggest that the model effectively exhibits important features of the accumulation of both volumetric and deviatoric deformation induced by drained cyclic loading over a large number of cycles.

Rutting is a major distress mode in flexible pavements, results from the repetitive loading caused by traffic movement. Pavement deformation consists of both recoverable (elastic) and unrecoverable (plastic) components. The continuous movement of vehicles contributes to the overall deformation in the flexible pavement system, involving all pavement components. In regions with hot climates or in the hot summer season, rutting tends to be more prominent due to the substantial reduction in the viscosity of the asphalt binder. This decrease in viscosity, which is inversely linked to rutting, occurs as temperatures rise, leading to a heightened susceptibility of the Hot Mix Asphalt (HMA) blend to rut formation. However, according to studies, a significant amount of permanent deformation takes place in the unbound layers beneath the asphalt course, it is therefore essential to prioritize attention on these layers. Temperature exerts besides viscosity a substantial impact on asphalt stiffness, leading to the transfer of higher vertical deviatoric stresses to the unbound layers beneath the asphalt course (base, subbase, subgrade). This research presents a study integrating the High Cycle Accumulation (HCA) model into a laminar model to determine permanent deformations in the unbound granular layer of flexible pavements and taking into account the temperature dependent stiffness of asphalt. Rutting depths at the end of the design lifetime were computed, accounting for seasonal stiffness variations. It was shown that the softer asphalt behavior significantly increases the development of ruts in the underlaying soil layers. The findings were compared with results obtained from mean annual temperature and the typical equivalent asphalt stiffness utilized in fatigue tests. Additionally, an analysis was conducted to assess whether the timing of road implementation influences settlements throughout the design lifetime. The results suggest that the sequence of seasons is most relevant during the first year of service, showing a distinct effect at that time. However, with a higher number of axle passes, the initial differences fade away, and the curves start to merge.