Experimental characterization of unbound granular materials subjected to high harmonic loads

Abstract

Unbound Granular Materials (UGM), used in base and subbase layers, play an important role in the structural performance of low volume roads with thin asphalt surface layers. They show complex stress dependent elasto-plastic behavior under cyclic loading. A proper understanding of the elastic and permanent deformation behavior of UGM is crucial to assess their suitability for the particular service. Full understanding of the material behavior is only possible by means of sophisticated test procedures such as the repeated load triaxial test. This testing method is quite complicated and the human and technological resources needed usually exceeds the budget of low volume road projects. Therefore, there is a need for simple and economical test methods to characterize the mechanical behavior of UGM under the action of high traffic loads. The paper shows the results of a test campaign using two different testing methods: a simple repeated load volumetric compression test and a more advanced repeated load triaxial test. The results of both tests showed a strong dependency of the bearing capacity and the permanent deformation behavior on the amount of water and stress level. The tests results are also used to develop a classification method for UGM.