Undrained cyclic behavior of soft marine clay involved combined principal stress rotation

In real-life costal engineering problems, the foundations are subjected to complex loads as increase in both deviator stress and major principal stress direction simultaneously. To investigate undrained deformation behavior and pore pressure accumulation of soft clay under different initial major principal stress directions, hollow cylinder apparatus (HCA) tests were carried out. The influence of intermediate principal stress coefficient was also considered. Combined principal stress rotation means that deviator stress and major principal stress direction simultaneously increase during shearing. It can be obtained that the deformation behavior and pore water pressure accumulation of tested samples are significantly influenced by intermediate principal stress coefficient b. Furthermore, the undrained behavior of tested natural soft clay samples is affected by the initial major principal stress direction. Moreover, the variation of stress and strain components is not synchronous with the increase of deviator stress and principal stress direction. The failures of soft clay specimens are controlled by strain other than pore water pressure involved combined principal stress rotation. The non-coaxiality of natural soft clay is influenced by different initial major principal stress direction significantly rather than b values.