Partially-drained deformation properties of anisotropically overconsolidated clay by triaxial tests with cyclic confining pressure

The subgrade clay in situ may be anisotropically overconsolidated, the traffic-induced dynamic stress field on the subgrade clay can be simulated more accurately by the simultaneous application of cyclic axial stress and cyclic confining pressure by the VCP test, and the partially drained condition represents a more appropriate field scenario for the cyclic response of subgrade clays under long-term traffic loading. To mimic the coupling of the above factors, this study performed a large number of cyclic triaxial tests on a overconsolidated clay in partially drained condition. The ratio of the radial consolidation stress to vertical consolidation stress (K), cyclic stress ratio (CSR) and the ratio of cyclic deviatoric stress amplitude to cyclic mean principal stress amplitude (eta ampl) are proposed, and their effects on the partially-drained permanent and resilient deformation behaviors of saturated clay are investigated. Test results show that the increase of consolidation-induced anisotropy (i.e., the decrease of K) leads to a remarkable increase of permanent axial strain, while it induces a first slight growth and then a decrease of permanent volumetric strain. Based on the shakedown theory, the allowable cyclic stress ratio separating the shakedown ranges of metastable and stable is determined, and it is unrelated to either K or eta ampl. The effects of eta ampl on the permanent axial strain are related to the shakedown range, and a uniform linear relationship is established between the permanent volumetric strain and cyclic mean principal stress amplitude. The anisotropically overconsolidated clay produces stiffness hardening in partially drained condition, in which the increase of both CSR and eta ampl promote the hardening. It is suggested the prediction and control of subgrade clay settlement in engineering practice should consider all the factors involved in this study.

Automated summary

This study investigates the effects of different factors on the permanent and resilient deformation behaviors of clay under partially drained conditions. The results show that an increase in consolidation-induced anisotropy leads to an increase in permanent axial strain. Based on the shakedown theory, an allowable cyclic stress ratio is determined, and a linear relationship is established between permanent volumetric strain and cyclic mean principal stress amplitude. It is suggested that the prediction and control of subgrade clay settlement in engineering practice should consider all the factors involved in this study.