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 (ηampl) 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 ηampl. The effects of ηampl 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 ηampl 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. •The increase of consolidation-induced anisotropy leads to a remarkable increase of permanent axial strain.•The effects of cyclic confining pressure on permanent axial strain are related to the shakedown range of clay.•The allowable CSR separating metastable and unstable ranges is determined and it is unrelated to either K or ƞampl.•The anisotropically overconsolidated clay produces stiffness hardening in partially drained condition.