Based on the concept of "thermal equivalent stress"

a new thermo-elastoplastic constitutive model

which is different from the traditional concept of plasticity that the plastic strain occurs below the normally yield surface

was proposed. In the model

the degree of saturation and skeleton stress were used as independent state variables that could describe the saturated and unsaturated soil behavior in a unified way. In addition

the concepts of sub-loading and superloading were also adopted that the overconsolidation and structure behavior of soil can also be described. The proposed model could simulate the mechanical performance of saturated/unsaturated soil at different temperature condition in consolidation tests and triaxial shear tests quite well.Meanwhile

the model was incorporated into soil-water-air-thermal multi-phase coupling field theory and a heating test in deep soft rock layer was simulated by FE-FD method. The agreement between the results of heating test and simulation confirmed the property of the proposed thermoelastoplastic constitutive model and numerical method. Thus

it could also be used in the analysis of energy piles and surround soils in the geothermal heat exchange system.