Thermoplasticity of Saturated Clays: Experimental Constitutive Study

Experimental results obtained from thermomechanical tests on three clays are analyzed in light of the constitutive equations of soil thermoplasticity presented in a companion paper. Heating and cooling drained tests at constant isotropic stress show a strong dependence of the elastic domain on temperature. Thermal sensitivity of elastic domain was found to be different in overconsolidated and in normally consolidated clays. Thermoplastic strain hardening builds up to compensate for thermal softening in normally consolidated clays at plastic compression during drained heating, if the constant stress is imposed. Triaxial compression tests at constant elevated temperatures show an increase in ductility and a decrease in dilatativity at high temperatures. Undrained heating tests show a significant water pressure buildup. At constant principal stress difference, the water pressure growth leads to an effective stress drop and an eventual failure at the critical state line. A temperature‐rate‐dependent non‐associative plastic flow rule is deduced from the comparison between experiments with drained heating at constant stress and loading at constant elevated temperature. Strength appears to be mildly affected by temperature. It decreases with temperature in overconsolidated clays and possibly increases in some normally consolidated clays.