A Double Volume Expansion Thermal-Mechanical Coupling Constitutive Model Considering Anisotropy

Volume expansion can occur in overconsolidated clay during shear loading and heating. However, the volume expansion mechanisms driving these two phenomena are different from each other, and it is important to propose a model that can be adopted to describe these two volume expansion phenomena. A new model is proposed to describe the two aforementioned volume expansion phenomena. Specifically, the following three innovative points are made: (1) The thermal-mechanical coupling yield surface is proposed in the p-q-T space, and the overconsolidation stress R can be used to reflect the loss effect of overconsolidation degree during the heating process. The modified unified hardening parameter is used to reflect the shear shrinkage of normal consolidated clay and the shear dilatancy of overconsolidated clay. (2) The nonassociative flow law is used to express the direction of plastic strain increment. The phase transformation stress ratio is expressed as an exponential function of the overconsolidated stress ratio, which can be used to reflect three typical volume deformation modes of overconsolidated clay: full shrinkage deformation, dilatancy deformation after contraction, and full dilatancy deformation. (3) A rotational hardening rule that reflects the anisotropic properties of initial partial consolidation of clay is introduced so that the proposed model can be adapted to reflect the increase of soil stiffness caused by K0 consolidation, as well as the hysteresis loop phenomenon for deviatoric strain and stress relationship curve caused by cyclic loading. The comparison results between prediction and test data show that the proposed new thermal-mechanical coupling model can be easily and conveniently applied to describe the deformation and failure behavior of overconsolidated clay relevant to thermal effects.