A Thermo-Hydro-Mechanical True Triaxial Cell for Evaluation of the Impact of Anisotropy on Thermally Induced Volume Changes in Soils

This paper describes a new thermo-hydro-mechanical true triaxial cell used for the evaluation of the impact of stress-induced anisotropy on thermally induced volume changes in saturated soils. Specifically, details of the experimental setup, instrumentation, thermal calibration of the device, experimental procedures, and typical measurements are presented in this paper. Principal stresses were applied to the sides of a cubical specimen with a side length of 178 mm independently using flexible bladders, while the pore water pressure and temperature were controlled at the top and bottom of the specimen using rigid plates with embedded heaters and fluid control ports. In the testing program, temperatures between 25 and 65 °C were applied in stages to four different specimens of compacted bonny silt which had been consolidated to different initial anisotropic stress states under quasi-plane strain conditions. Consistent volumetric contraction was measured in each of the specimens during heating, regardless of the initial stress state. However, for specimens with a greater initial principal stress difference, the soil was observed to expand in the direction of the minor principal axis and contract in the direction of the major principal stress during heating. Relatively consistent elastic volumetric and axial contraction was noted during cooling regardless of initial stress state. The results from this preliminary investigation indicate the importance of measuring the impact of temperature changes in the directions of anisotropic stresses as part of the design of thermally active geotechnical systems.

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