UC San Diego

© 2015 Springer International Publishing Switzerland This study presents an evaluation of yielding mechanisms for unsaturated, compacted silt using drained triaxial compression tests with control of elevated temperatures and high suction magnitudes. After anisotropic compression, some compacted silt specimens were heated by approximately 40 °C before a suction of approximately 300 MPa was applied, while others were heated after suction application. A frictional response was observed for the specimens sheared under high suction magnitudes, in the form of a consistent increase in peak shear strength with increasing net confining stress. An effective stress analysis was used to evaluate the trends in the peak shear stress and the role of stress history for the different specimens. A single peak failure envelope was observed when the shear strength data was interpreted in terms of the mean effective stress. Changes in preconsolidation stress were estimated by identifying the intersections between a thermo-elasto-plastic yield function and the experimental peak shear strength values. Soil specimens heated before application of high suction values had lower peak shear strengths than reference specimens at high suction and ambient temperature. This behaviour is consistent with thermal softening trends observed in soils heated under low suction values. However, soil specimens heated after suction application had greater peak shear strengths than the reference specimens. This indicates heating under high suction results in hardening. The impact of suction on the preconsolidation stress was found to be better represented by a power law model at high suction magnitudes than other available models. The estimated preconsolidation stress values were used to evaluate the impacts of stress history on the thermal volume change response, which matched well with data from tests on saturated specimens.