Increase of Resilient Modulus of Unsaturated Granular Materials During Drying After Compaction

Abstract

The stiffness of a graded aggregate base (GAB) layer is stress- and moisture-dependent and changes throughout the depth of the layer due to different induced stresses at different depths and over time as the moisture content of the GAB changes. The lightweight deflectometer (LWD), a common in-situ stiffness test device- measures the surface deflection induced by an impulse on the soil and reports the overall stiffness assuming the section as an elastic homogeneous half-space. Consequently, there is a discrepancy between the true modulus of the finite-thickness GAB material (E GAB-EQV ) and the modulus reported by LWD (E LWD ). This paper simulates an LWD loading on a 200 mm GAB layer at 91% initial saturation on an infinite subgrade and compares E GAB-EQV to E LWD . The evaporative flux corresponded to a climatic condition having an average temperature of 24°C and average relative humidity of 60% with no precipitation. The simulation results showed that the stiffness of the newly installed GAB layer increased by nearly 100% during the first 10 days after placement. The stiffness increase predicted by the LWD measurements was significantly less, suggesting that modulus values measured by LWD should be interpreted with caution. E GAB-EQV can be predicted using the initial E GAB-EQV of the layer and the average degree of saturation of the layer in the subsequent days with less than 10% error.