Impact of the loading rate on the unsaturated mechanical behavior of compacted red clay used as an engineered barrier

To explore the feasibility of the application of a compacted red clay as an engineered barrier in landfills, the effect of the loading rate on its unsaturated mechanical behavior has been investigated through a series of triaxial shear tests in this work. The loading rate was changed stepwise numerous times at the designed matric suction and net confining pressure. Based on the deviator stress–axial strain curves, the coefficient of rate-sensitivity (β) was obtained. A model describing the relationships among stress, strain, strain rate, time, and matric suction was also proposed. The experimental results show that the value of β is the largest at the beginning of loading, then decreases sharply. With time and strain increasing, the value of β does not change significantly. At a given value of the net confining pressure, β is larger at larger matric suctions. Moreover, under different matric suctions the respective stress–strain curves are all isotachic. The proposed model was able to describe the effect of the loading rate on the behavior of the red clay almost satisfactorily. These results might be beneficial in the design of compacted clay barriers in landfills under unsaturated conditions.