On the Influencing Factors of Non-asphalt Originated Rutting in Flexible Pavements

Rutting can substantially impact pavement serviceability and driving safety. Since most of the permanent deformation develops in the unbound layers beneath the asphalt course, the focus should be on these layers. In this research, rut depths were calculated and analyzed using the high-cycle accumulation model, where the resilient response and cyclic strain amplitude were determined through finite element analysis. Consequently, settlement depression curves were described for various subgrades and cross-sections. It was observed that grain size distribution, particularly the uniformity coefficient, plays a decisive role in rutting depth. Analysis of the relationship between settlements and axle loads indicates that the calculated settlements demonstrate a linear increase relative to the axle load. For various axle loads, the number of axle passes required to induce an equivalent settlement to the standard axle was established. The possibility to reduce the depth of ruts by increasing the thickness of the subbase was also investigated. It was found that the predicted rutting is highly influenced by the particle shape (angular, rounded, or mixed material) of the subbase. It was found that the primary portion of permanent deformations occurs within the subgrade.