Shear Wave Velocity Response of Compacted Kaolin during Drying-Wetting Cycles

Previous studies indicate that that post-compacted changes in moisture and suction significantly influence small strain response, often this is not routinely monitored during operation. Thus, assessing the impacts of seasonal variation on performance is critical for gauging the geomechanical behaviour of compacted soils underlying typical transport infrastructure. In this paper the influence of drying-wettingcycles on small strain stiffness is investigated on compacted kaolin specimens by measuring shear velocity using ultrasonic testing methods. The drying-wetting cycles were applied to specimens using fixed levels of gravimetric water content. This more closely mimics near surface unsaturated site conditions rather thanadopting fixed suction levels using the axis translation technique. As expected, the results show that the shear wave velocity exhibits a hysteretic response during drying-wetting cycles. However, as the cycles are controlled by gravimetric water content, higher shear wave velocity values were recorded for the dryingpaths rather than wetting paths as previously reported in suction controlled testing. Furthermore, for the subsequent drying-wetting cycle, the shear wave velocity continues to show an hysteretic response while also exhibiting increasing velocities for a given gravimetric water content level, indicating that specimensare undergoing some form of hydraulic ageing.