Creep behavior of oil sand and its constitutive model

Oil sand is a kind of sedimentary sands, whose pores are mostly filled with natural bitumen. As a strain softening material, the oil sand exhibits more complex creep behavior than the strain hardening materials, such as loose sand and normal consolidated clay. A series of triaxial creep tests are performed on the oil sand to obtain its creep behavior under different stress and strain states. The potential for creep is compared to that for plastic deformation. The concept of equivalent deformation processes is proposed and its microscopic mechanics is presented. The relation between creep rate and time, and that between creep rate and irreversible strain are discussed. An internal-variable creep model for the oil sand is proposed. In the model, the irreversible strain is considered as the internal variable for the description of oil sand creep. The creep behavior of both strain hardening and softening soils is postulated according to the critical state theory. The influence of shear band on the creep behavior of the oil sand is also investigated.