Mechanistic prediction of corrugation in unsealed roads under climatic influence: insights and design chart guidance

Corrugation, a common failure mode in unsealed roads, emerges from repeated tyre–road interaction under variable environmental and loading conditions. This paper presents a mechanistic modelling framework to predict the onset of corrugation by incorporating climate-driven moisture variation, unsaturated shear strength degradation and friction mobilisation at the tyre interface. Laboratory tests and climatic simulations using finite element-based HYDRUS-1D software were employed to capture moisture-dependent changes in shear strength parameters for a crushed rock class IV base layer. Estimated temporal variations in bearing capacity revealed that the upper 50 mm of the pavement is highly sensitive to climatic fluctuations, with effective cohesion decreasing from about 11 kPa under dry conditions to approximately 4 kPa under extreme wet conditions. Bearing capacity frequently dropped below 300 kPa, aligning with observed corrugation during field monitoring. The dynamic friction coefficient peaked at 0.87 under dry conditions, indicating a high potential for shear stress mobilisation. Design charts were developed to assess material suitability as a function of effective cohesion, friction angle, surface saturation and dynamic friction. The proposed framework provides a predictive tool for evaluating the susceptibility of unsealed roads to corrugation, enabling informed decisions on material selection, treatment and maintenance planning.