Dynamics of washboard road formation driven by a harmonic oscillator

History-dependent growth and reduction of the ripples formed on a swept granular track

When a solid object or wheel is repeatedly dragged on a dry sandy surface, ripple patterns are formed. Although the conditions to form ripple patterns have been studied well, methods to eliminate the developed ripple patterns have not been understood thus far. Therefore, history-dependent stability of the ripple patterns formed on a sandy surface is investigated in this study. First, the ripple patterns are formed by sweeping the flat sandy surface with a flexible plow at a constant speed. Then, the sweeping speed is reduced, and the variation of ripple patterns is measured. As a result, we find that the ripple patterns show hysteresis. Specifically, the increase in amplitude of ripples is observed when the reduced velocity is close to the initial velocity forming the ripple pattern. In addition, splitting of ripples is found when the reduced velocity is further decreased. From a simple analysis of the plow's motion, we discuss the physical mechanism of the ripple splitting.

Corrugation of an unpaved road surface under vehicle weight

Road corrugation refers to the formation of periodic, transverse ripples on unpaved road surfaces. It forms spontaneously on an initially flat surface under heavy traffic and can be considered to be a type of unstable growth phenomenon, possibly caused by the local volume contraction of the underlying soil due to a moving vehicle's weight. In the present work, we demonstrate a possible mechanism for road corrugation using experimental data of soil consolidation and numerical simulations. The results indicate that the vertical oscillation of moving vehicles, which is excited by the initial irregularities of the surface, plays a key role in the development of corrugation.