Effects of principal stress rotation on deformation behaviour of clay under partially drained and undrained conditions

Subgrade clay in regions with busy roads is more likely to exhibit partially drained than undrained cyclic behaviour considering the long duration of traffic loads. To study the deformation response of soft clay under the two drainage conditions, cyclic tests were conducted on a dynamic hollow cylinder apparatus with and without principal stress rotation. The concept of transitional cyclic stress ratio (CSR) was proposed. When the CSR is lower than the transitional CSR, the partially drained condition causes permanent axial strain enlargement when compared with the undrained conditions; Once the CSR exceeds the transitional CSR, the partially drained condition markedly restricts the development of the permanent axial strain. Moreover, both critical and allowable CSR in the partially drained tests are higher than in the undrained ones, and the allowable CSR under different drainage conditions is smaller than the transitional CSR. Therefore, the influence of the partially drained condition on the cyclic deformation of clay must be considered in practice. Two empirical models were proposed to predict the permanent volumetric strain and permanent axial strain under the partially drained condition