The loading thermal (LT) yield curve is first introduced to consider the effects of temperature on the preconsolidation pressure change for unsaturated clays. Based on the concept of true strength and the calculation method of the potential failure stress ratio

the equation of the critical state stress ratio for unsaturated clays under different temperatures is deduced. The LT yield curve is then combined with the loading collapse (LC) yield curve which is used to consider the effects of suction on the preconsolidation pressure change for unsaturated clays

by which the loading thermal collapse (LTC) yield surface is presented. Therefore

the effects of both temperature and suction on the preconsolidation pressure change are considered by the LTC yield surface. After that

a constitutive model for normally consolidated unsaturated clays considering temperature effects is proposed based on the framework of the critical state soil mechanics; and it is extended to consider the properties of overconsolidated unsaturated clays. Compared with the Barcelona basic model

the proposed model requires only one additional parameter to consider the behavior of the decrease of preconsolidation pressure with an increase of temperature. The proposed model can describe the effects of temperature

suction and OCRs(overconsolidation ratios) on the stress-strain behavior for clays. Model predictions and test results show that heating will cause an increase of the strength for normally consolidated unsaturated clays at a given suction. The overconsolidation behavior decays or even disappears by either heating or wetting for overconsolidated unsaturated clays

consequently

the behavior of softening and shear dilatancy will be decayed