Experimental study of stress-strain properties of intact soft clay considering the change of principal stress direction

Experimental study of stress-strain relationship of normally consolidated intact soft clay in Hangzhou under undrained fixed shear of principal stress direction and monotonic rotation of principal stress axis had been done,which was used to reflect the soil properties response to the monotonic rotation of principal stress axis under real engineering conditions.It was found that under the fixed principal stress direction shear,strain components at different principal stress direction had quite different development levels,but the values of most samples' critical octahedral strain were comparatively close.Meanwhile,when the octahedral strain reached 5%,the development level of most samples' shear strengths had been closed to,even exceeded 90%.When additional stress path of monotonic rotation of principal stress axis was added to fixed shear of principal stress direction,samples critical strain components would not change obviously as long as the final failure principal stress directions were similar.But the direction of principal stress increment and the principal strain increment showed non-coaxiality during the rotation of principal stress axis;and with the development of shear stress level till critical state,such non-coaxiality became more obvious.The experimental results showed that due to the existence of initial anisotropy and viscoplasticity,it was not proper to describe the stress-strain relationship during and after rotation of principal stress with associated flow rule.