Mechanical behaviour and loading rate dependency of gypsum-mixed fine-grained soils

Gypsum is regarded as an environmentally friendly binding material and is widely used to enhance the engineering properties of soft fine-grained soils. However, the time-dependent strength and deformation characteristics of fine-grained soils stabilised with gypsum have not yet been thoroughly investigated and rational evaluation of these characteristics will assist in the formulation of cost-effective and reliable design approaches. In this study, the time-dependent mechanical behaviours of gypsum-mixed fine-grained soil (GMFS) specimens were investigated under unconfined monotonic loading conditions, considering ageing periods of 3–90 days and five different loading rates (LR = 0.0005–1.0%/min). The results revealed that the unconfined compressive strength and stiffness of the GMFS specimens initially decreased with ageing and finally became stable after 14 days and 28 days of ageing for water/gypsum ratios of 1.30 and 1.60, respectively. Furthermore, the strength and stiffness of the GMFS specimens increased with an increase in LR.