Strain evolution of saturated clays under cyclic loadings in three-dimensional stress condition

The strain evolution of saturated clays under cyclic loadings has been studied by means of various laboratory testing methods, aiming for the accurate simulation of engineering conditions such as the consolidation states of clays, cyclic stress paths of external loadings and boundary conditions in situ. Considering that the subgrade clays are usually overconsolidated rather than normally consolidated, the drainage condition is normally partially drained instead of undrained under long-term cyclic loadings, and the cyclic stress paths are in three-dimensional stress state, this study explores the three-dimensional strain characteristics of both normally and overconsolidated clays in partially drained condition based on a true triaxial apparatus. Emphasis are put on the effects of cyclic stress ratio (CSR), overconsolidation ratio (OCR) and coefficient of cyclic intermediate principal stress (b(cyc)) on the accumulation of permanent strain components including major, intermediate, minor principal strains, and volumetric strain. Test results show that the relative magnitudes of strain components are strongly influenced by both b(cy)(c), and OCR, while the accumulated directions of strain paths tend to be identical for various b(cy)(c), values. The increase of b(cyc) leads to a linear growth of permanent volumetric strain for both normally and overconsolidated clays, while the permanent major principal strain shows a firstly increasing and then decreasing trend versus the increase of b(cyc). For the normally consolidated and overconsolidated clays, the largest permanent major principal strains are achieved at around b(cyc) = 0.4 and 0.2, respectively. The accumulation of permanent intermediate principal strain is always promoted by the increase of b(cyc). In addition, the development of permanent major principal and volumetric strains with cycle number is analyzed in the double logarithmic plane, which are found to be combined by two linear parts.