Effect of drainage states on dynamic behaviours of Ningbo clay under uniform cyclic loading

In this study, the actual drainage condition of in situ soft clay is partially drained and the natural soft soil was subjected to long-term uniform cyclic loading. Cyclic triaxial tests were conducted on remoulded samples to analyse the effect of drainage condition on the dynamic behaviour of Ningbo clay. The results showed that when the cyclic stress ratio (CSR) was small, the accumulated axial strain under undrained conditions was larger than that under partially drained conditions; however, when the CSR was high, the accumulated axial strain in the undrained condition reduced. The resilient strain gradually decreased after a large number of cycles under partially drained conditions, while it increased more significantly with an increase in CSR during the experiments under undrained conditions. With increasing cycle numbers, the pore pressure initially increased and then decreased with a peak value under partially drained conditions, while the pore pressure tended to become stable under undrained conditions. On the basis of the test results, equations for permanent axial strain and pore pressure considering the effect of drainage conditions are proposed, which can predict the dynamic responses of in situ subsoils under long-term uniform cyclic loading.