Geothermal structures, such as energy piles, are subjected to cyclic changes of temperature that affect the properties of soil-structure (or pile) interface and surrounding soil. To evaluate the effects of temperature changes on the shearing behaviors of soil and soil-pile interface, a series of direct shear tests with controlled temperature were conducted. To characterize the soil properties, the direct shear device was placed in a temperature controlled chamber and the temperature of the soil was monitored. The soil tests were conducted at temperatures of 4, 21, 30, and 38°C. Furthermore, the effect of cyclic temperature change was investigated using a small number of cycles (maximum of four cycles in this paper). The non-isothermal effects were also characterized using a modified direct shear test device where the bottom half of the soil box was replaced by a concrete plate. The soil-pile interface properties were measured at the same temperatures and normal stresses as the soil tests. Finally the results of the soil and soil-pile interface were compared.
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