Impact of Drying/Wetting on Shear Stiffness and Shear-Induced Volume Change Behaviours of Unsaturated Silty Clay

To further improve the understanding of the impact of drying/wetting on mechanical behaviours of unsaturated soils, this paper presented experimental results of suction-controlled triaxial tests on a slurry-consolidated silty clay with different drying/wetting cycles, matric suctions and net confining pressures. Test results show that, even if the same net confining pressure and matric suction were followed during triaxial shearing, the specimens that experienced six drying/wetting cycles ( D – W -6) produced higher shear stiffness in the early stage of shearing and lower volumetric strain compared to those of specimens that have not been subjected to any drying/wetting history ( D – W -0) at low matric suction condition. The stress–strain relationship of soils tends to alter from strain-hardening to strain-softening after drying/wetting. This is because the maximum matric suction experienced in drying/wetting process is similar to the pre-consolidation pressure, and thus the specimens became overconsolidated. However, D – W -6 shows a similar stress–strain relationship with D – W -0 under matric suction of 200 kPa due to the shear stiffness arisen from the irreversible volume compression (overconsolidation), which is counterbalanced by that contributed by its lower degree of saturation. The impact of drying/wetting on mechanical behaviours of unsaturated soils is always affected simultaneously by irreversible volume compression and lower degree of saturation. The overall influence of drying/wetting depends on the proportional effects of the two factors.