Hydro-mechanical behavior of unsaturated unbound pavement materials under repeated and static loading

Climatic events such as precipitation result in unbound structural layers of pavements being in a partially saturated condition during their service life. With unsaturated testing being relatively complex and costly, the presence of relatively low matric suction in granular geomaterials, practitioners have been reluctant to explore the utilization of unsaturated geomechanics in the analysis and design of the mechanical behavior of pavement structural layers. In this research, unsaturated mechanical characteristics of three types of recycled geomaterials were firstly investigated using repeated load triaxial testing and the incorporation of their soil–water characteristics in the analysis of their resilient moduli response. This was to demonstrate the importance of understanding the unsaturated mechanical behavior of compacted granular material. Next, a virgin compaction surface (VCS) was developed within a moisture content-based framework to interpret the loading, unloading and wetting-induced volume change of the compacted materials. Outcomes of this research, for the first time, extend the application of the well-established Monash Peradeniya Kodikara (MPK) framework, originally developed for fine cohesive soils, to granular materials. A distinctive attribute of the proposed approach is the relative simplicity in the testing methodology by utilizing the conventional geotechnical testing equipment. The findings of this research can be used for estimation of the settlement of a granular structural layer that is compacted, loaded and then wetted through precipitation or flooding.