LAW OF THERMODYNAMIC BEHAVIOR FOR UNSATUR ATED SOILS - IDENTIFICATIONIN-SITU OF THERMAL COMPRESSION INDEXES

This paper deals with the thermo-hydromechanical behaviour of nonsatur ated soils. The constitutive relationship presented herein allows for the prediction of the settlement or swell of an unsaturated soil under nonisothermal oedometric conditions. Mechanical, hydraulic, and therm al compression indexes are considered for stress, capillary pressure, and temperature variables, respectively. The implementation of the rel ationship in a prediction scheme requires preliminary characterization of these indexes. The stress-strain and water volume change relations hips are first presented from a semiempirical point of view for a nons aturated soil element under nonisothermal conditions. These relationsh ips allow for the expression of a thermo-hydromechanical constitutive law for nonsaturated soils and propose a relationship for the change i n the soil water content. The thermal compression indexes are then det ermined for a clayey silty sand, first using a reverse method and then a direct method. This determination is made from experimental data re corded on a prototype involving heat storage in an aquifer. The values of these thermal compression indexes are finally compared with the la boratory values obtained in a thermal triaxial cell on samples of the same soil.