Effect of Fines Content on Cyclic Strength Development of Sand–Clay Mixtures under Cyclic Loading: A Process Evaluation Using Energy Methods

Abstract

Evaluating the cyclic strength development using energy-based methods is a novel concept in studying the dynamic properties of sand–clay mixtures under cyclic loading. In this study, a series of undrained cyclic triaxial tests were conducted on sand–clay mixtures, and the performance of different fine-grain contents on the dynamic properties and the energy dissipation of sand–clay mixtures was investigated based on the energy-based methods. The results demonstrated a gradual increase in the cyclic strain amplitude and the residual axial strain with increasing fines content (FC) under cyclic loading with a controlled cyclic stress ratio; in contrast, the accumulation of pore-water pressure slowed down. An initial decrease in the cyclic strength of the mixtures was observed with an increase in their fines contents; however, further increasing the FC enlarged the cyclic strength of the sand–clay mixtures. This transition was observed when the threshold fines content reached about 30%. The viscous energy dissipation ratio (VEDR), which is a nondimensional energy ratio based on the relationship between cyclic stress and strain and reflects the characteristics of dynamic properties, was utilized to compare three critical phase transition points, namely, VEDRvalley, VEDRpeak, and VEDR5%strain, in the energy dissipation of the sand–clay mixtures. Based on the VEDR results, the cyclic strength development indexes were established. Furthermore, low-vacuum environmental scanning electron microscopy revealed that as the FC increased, the particle composition of the sand–clay mixtures transitioned from predominantly coarse-grained to fine-grained, resulting in a change in the cyclic behavior of the mixtures from sandlike to claylike. The cyclic strength development indices provided further insights into and quantified the effect of fines contents of the sand–clay mixtures on their cyclic strength development process.