Many geotechnical problems

such as development and utilization of geothermal resources and nuclear waste disposal

need to consider the effect of temperature on the stress and strain properties of saturated and unsaturated soils. To consider the effects of temperature and suction on the preconsolidation stress change for soils

expressions of preconsolidation stress for soils at different temperatures are first introduced. After that

combining the expression with the yield surface of unified state parameter model for clay and sand

considering the influence of temperature and suction on the normal consolidation line and critical state line

a unified thermo elastoplastic constitutive model describing the temperature effect of saturated and unsaturated soils is proposed. The proposed constitutive model is divided into saturated part (suction less than the air entry value or bubbling pressure at certain temperature) and unsaturated part (suction more than the air entry value or bubbling pressure at certain temperature). The comparisons between the model predictions and experimental data indicate that the proposed model can quantitatively predict the stress and strain properties of saturated and unsaturated soils at different temperatures.