An investigation of the effects of thermal gradients on the attenuating creep behaviour of model piles in frozen sand

There is a concern that when heated basements are thermally insulated, they will experience frost-heave problems due to adfreezing. The writer's earlier work provided an explanation for the apparent lack of adfreezing problems. It was reasoned that heat flowing away from a basement wall and the resulting moisture movement sufficiently reduced the adfreezing bond strength to prevent the transfer of damaging displacements. In this study, model piles embedded in a frozen sand are used to investigate this hypothesis. Recognizing that frost-heave is a time-dependent process, this study begins by examining the attenuating creep behaviour of the model piles when sample conditions are isothermal. Analysis of isothermal test results using the power-law model reveals that sample behaviour varies. To avoid problems inherent with sample variability, methods of step-load testing are refined and the application of the power-law model to step-load test results is developed. Using these developments, and the isothermal test results as a reference, this study proceeds to examine the influence of thermal gradients on the creep behaviour of the model piles. Changes in the resistance of the frozen sand to time-dependent displacements are shown to be directly related to the magnitude and direction of the thermal gradients in the soil surrounding the model piles. The loss of resistance, which occurs when heat flows away from the pile, is shown to be related to the movement of moisture in the frozen soil. Such findings offer support for the validity of the original hypothesis. While the investigations presented here represent an initial step toward verifying this hypothesis, it is hoped that future investigators will carry on the research efforts, and that they will be guided by the methods used here.