Response of Cohesive-frictional Soils Under Thermo-Controlled Cyclic Simple Shear Testing: Preliminary Observations

A newly manufactured cyclic simple shear (CSS) apparatus has been upgraded to investigate the dynamic response, namely, shear modulus and damping ratio, of cohesive-frictional soils under controlled moisture, confinement, and thermal conditioning of the pore-fluids, from 23oC (room temperature) to 60oC. A digital convection heater, featuring a full set of heating elements and a thermocouple, was adapted to the main cell of the CSS apparatus for measurement and control of thermal gradients in the test samples. A thorough thermo-calibration of the upgraded CSS chamber was accomplished prior to thermo-controlled testing to ensure proper heating and heat distribution within the soil samples. Preliminary testing was aimed at investigating the effects of increased temperatures on shear modulus and damping ratio of cohesive- frictional soils for a wide range of shear strain amplitudes (0.001% to 10%). Results suggest that increased temperatures cause a decrease in peak shear stress for a fixed shear strain amplitude, therefore resulting in a decrease in shear modulus and, conversely, an increase in damping ratio. A reduction in soil stiffness was also evident at lower compaction-induced suctions (higher moistures) regardless of the thermal conditioning eventually induced on the test soil.