A constitutive model for soft rock with both strain softening and negative dilatancy

It is well known that soft rocks exhibit strain-hardening and strain-softening during the shearing process. Under the confining pressure near the consolidation yield stress, it has been reported that soft; rocks exhibit both strain softening and negative dilatancy. In this paper, we have extended the constitutive model proposed by Adachi and Oka in order to describe the negative dilatancy with strain softening behavior by considering the change in the initial volumetric component of stress history tensor and shrinkage of the overconsolidated boundary surface due to deterioration of the internal structure. The application of the extended model for sedimentary soft rocks is shown with good agreement to the experimental results.