A thermo-elastic-plastic model for unsaturated soils has been presented based on theeffective stress principle considering the thermo-mechanical and suction couplingeffects. The thermo-elastic-plastic constitutive equations for stress-strain relations of thesolid skeleton and changes in fluid content and entropy for unsaturated soils have beenestablished. A plasticity model is derived from energy considerations. The modelderived covers both associative and non-associative flow behaviours and the modifiedCam-Clay is considered as a special case. All model coefficients are identified in termsof measurable parameters.To verify the proposed model, an experimental program has been developed. A series ofcontrolled laboratory tests were carried out on a compacted silt sample using a triaxialequipment modified for testing unsaturated soils at elevated temperatures. Imageprocessingtechnique was used for measuring the volume change of the samplessubjected to mechanical, thermal and hydric loading.It is shown that the effective critical state parameters M, κ and λ are independent oftemperature and matric suction. Nevertheless, the shape of loading collapse (LC) curvewas affected by temperature and suction. Furthermore, the temperature change affectedthe soil water characteristic curve and an increase in temperature caused a decrease inthe air entry suction.The simulations from the proposed model are compared with the experimental results.The model calibration was performed to extract the model parameters from theexperimental results. Good agreement between the results predicted using the proposedmodel and the experimental results was obtained in all cases.
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