Small-Strain Stiffness of Cohesive-Frictional Soils from Thermo-controlled Constant Water Content Resonant Column Testing

The impact of thermal gradients on the stiffness response of soil materials subjected to monotonic loading has been reasonably well documented. The combined effect of simultaneous thermal and cyclic loadings on soil stiffness, however, has not been as thoroughly investigated. In the present work, a comprehensive series of thermo-controlled constant-water content resonant column (RC) tests was carried out to experimentally assess the effect of increasingly elevated temperatures on small-strain stiffness properties, namely maximum shear modulus and minimum damping ratio, of three different types of cohesive-frictional soils. An existing RC apparatus was upgraded by the incorporation of immersion heaters and a thermocouple inside the main RC cell to control and monitor the thermal conditioning of the test samples. A thorough calibration of the upgraded RC device was first performed to determine the suitable thermal-equalization time required to reach reasonably steady heat distribution within the typical RC test samples of each type of soil. Results from the series of thermo-controlled RC tests showed a mostly detrimental effect of increasing temperature on the small-strain shear moduli of cohesive-frictional soils. The small-strain damping ratios, accordingly, either remained unchanged or experienced a gradual increase with increasing soil temperature.