Ageing and viscous effects on the deformation and strength characteristics of cement-mixed gravelly soil in triaxial compression

To investigate ageing and viscous effects on the strength and deformation characteristics of densely compacted cement-mixed gravelly soil as well as their interactions, a series of drained triaxial compression (TC) tests were performed on moist specimens compacted at water contents close to the optimum, employing several specially designed loading histories. Ageing effects were evaluated by using specimens cured at unconfined conditions as well as different anisotropic TC stress conditions for different periods, while loading rate effects due to viscous property by changing stepwise the strain rate and applying drained sustained loading during otherwise monotonic loading (ML). The strength and pre-peak stiffness generally increased by ageing (i.e., curing in this case), like young concrete. Noticeable loading rate effects due to viscous effects were observed, of which the trend was rather independent of curing period (i.e., ageing period). When ML was restarted at the original strain rate following sustained loading at an anisotropic stress state, the material became very stiff in a relatively large stress range that developed by coupled effects of ageing and viscosity. For the same total ageing period until failure, the peak strength became larger when aged at a higher shear stress for a longer period when compared to the value predicted based on the peak strength when aged unconfined or confined without a shear stress. The viscous property was quantified. The basic features of viscosity were found to be similar to those of unbound granular materials.