Thermomechanical Triaxial Cell for Rate-Controlled Heating-Cooling Cycles

Abstract

This article presents the development, calibration, and performance of a triaxial cell developed to study the thermomechanical behavior of soils under controlled heating and cooling rates and sinusoidal temperature changes mimicking real field conditions. This cell uses bipolar thermo-electrical devices to fully control the applied thermal loads. The cell can accommodate specimens up to 75 mm in diameter with a height-to-diameter ratio of 2 to 2.5. Tested soil specimens can be subjected to temperatures ranging from −5°C to 70°C with the specimen temperature change rate ranging from ±0.001°C/min and ±0.4°C/min. First, the modifications implemented on a conventional triaxial cell are presented to facilitate controlling of the boundary temperature applied to the specimen and the applied heating/cooling rates. Then, the thermal calibrations of the modified triaxial cell under different isotropic stresses and temperatures in drained and undrained conditions are presented. Finally, the capabilities of the modified triaxial cell are demonstrated using a thermomechanical test on a remolded kaolinite clay subjected to a drained heating-cooling cycle. The specimen was saturated and consolidated under 500 kPa confining stress at 20°C; then it was subjected to a drained thermal cycle (20 – 70 – 10 – 20°C) using a temperature change rate of ±0.1°C/min. Upon completing the thermal cycle, the specimen was sheared under undrained conditions at 20°C. The results of this test show a thermally induced contractive plastic volume change agreeing with the thermomechanical behavior of saturated normally consolidated clays in the literature. Furthermore, the drained heating-cooling cycle caused a dramatic increase in the undrained shear strength compared to the value measured at 20°C.