Effective stress concept for the effect of hydraulic hysteresis on the resilient behaviour of low traffic pavements

This paper presents the influence of the unsaturated state and especially the different hydraulic behaviours during the wetting and drying cycles (hysteresis phenomenon) on the resilient behaviour of unbound granular materials for roads. In this context, the soil water retention curve (SWRC) of a compacted clayey sand was initially obtained for both wetting and drying paths. These experimental results were then complemented by a series of direct shear tests. Finally, repeated load triaxial tests (RLTTs) were also performed at the same water contents on both wetting and drying paths. It can be stated that the samples prepared on the wetting path showed higher resilient volumetric strains compared to those prepared on the drying path, especially at low water content. However, the influence of the hysteresis phenomenon is less evident for the resilient shear strains. Different effective stress concepts based on the SWRC and shear test results were also added to the classical Boyce model generally used to estimate the resilient behaviour based on the total stress concept. The estimated effective stresses of the RLTT give the best correlation coefficient for all water contents of the wetting and drying paths. Finally, finite element calculations, carried out with CAST3M, were performed to compare the deflection of a low traffic pavement at saturated/dry conditions for the subgrade soil. The asphalt concrete layer and the base layer were taken the same for both conditions. The influence of the hysteresis phenomenon on the deflections is more pronounced at the dry condition.