Theoretical modelling of the washboard phenomenon on unpaved roads

Washboard, or corrugation, is a common phenomenon of soil deformation on unpaved roads. Undulations appear on granular material roads due to the velocity and mass of the vehicles. This work proposes a theoretical model for analysing the washboard phenomenon on unpaved roads that allows computing the soil's permanent displacements and the forces produced by the passage of a wheel. The model uses the dynamic equilibrium, soil-bearing capacity, and macro element models based on the theory proposed by Wolf. This model was validated by comparing experimentally measured deformations and forces on a circular sandy path with an instrumented rotating wheel. A parametrical analysis was also conducted to understand the variables strongly related to the washboard phenomenon. This analysis focuses on the effect of the mechanical soil properties and the wheel velocity on the soil's permanent displacement and contact forces. The results suggest that undulations start to form at a certain critical speed. The analysis also shows that cohesion, more than friction angle, could be important in reducing road corrugation.