Abstract：Contrary to hard rocks, the plastic deformation of soft rocks during the initial creep stage occurs more obviously. The traditional component models can be used to describe the visco-plastic behaviour of the geomaterials, but only when the stress value is beyond the yield point. This paper proposes the plastic deformation as a variable in the disturbance function, in the framework of the Disturbed State Concept, to describe the evolution characteristics of elastic-plastic states during loading and unloading. In addition, the evolution of the disturbance equation in time is further investigated and analyzed according to the relationship between plastic deformation and time. The Burgers model is applied to the relative intact state, while the Bingham model is employed to describe the fully adjusted state. The disturbance function is utilized to combine the two states. Following this approach, the creep constitutive model for soft rocks are presented. Comparison with the creep test results of argillaceous shale indicates that the proposed disturbance state constitutive model accurately captures the temporal evolution of the transformation process from relative intact state up to fully adjusted state. Furthermore, the proposed model can better handle both nonlinearity and stage coordination, while it provides a more profound description of the initial, stable and accelerating creep stage of soft rock
2017, Vol. 38 
