Unpaved roads generally undergo heavy loads. In that context, a rigorous design method for that kind of roads is desirable, based on mechanistic-empirical principles and on subgrades mechanical behaviors. A mechanistic design approach, combined with empirical damage laws, allows to optimize unpaved roads structures and to reduce maintenance and construction costs.
Therefore, the goal of this project is to elaborate a mechanistic-empirical method for design of unpaved roads. First, a calculation model was developed in order to determine the stress and strain level in the pavement structure This model consists of an elastic multilayer road modeling, using Odemark’s transformation and Boussinesq’s equations. Then, empirical damage curves for unpaved roads were developed. Finally, this work has allowed to create design charts.
A two-step approach was adopted for the development of the transfer functions. The first one was, to establish rutting threshold values according to suitable functional and structural road conditions. Then, the development of allowable strain criteria that combines the calculated theoretical strains with the observed strains on real roads was performed.
Laboratory testing was performed on typical road samples using an accelerated load simulator. The instrumentation of the structures was designed to measure the resilient and permanent vertical deformation at the top of the subgrade. The rutting rate was also measured during the tests.
