Effects of Temperature and Thermal Cycles on Frictional Behavior of Kaolin–Concrete Interface

Abstract

Frictional energy piles have been emerging as a proenvironmental means in the industry to exploit shallow geothermal energy. A growing concern for energy piles is their bearing capacity typically subjected to temperature variations. To better understand the temperature-dependent behavior involving bearing capacity, herein a series of direct shear tests were carried out to examine the effects of temperature and thermal cycles on the frictional behavior of the pile–soil interface for energy piles. The pile–soil interface consisting of fine-aggregate concrete and kaolin clay was tested under four normal stress levels, i.e., 50, 100, 200, and 300 kPa. The results suggest that: (1) a positive correlation may exist between temperature and the shear strength of the pile–soil interface; (2) the adhesion of the interface may vary with temperature in terms of a nonmonotonic function; and (3) the shear strength of the interface appears to decrease with an increasing thermal cycle and/or an increasing fluctuation amplitude of temperature within a temperature cycle. The experimental data obtained here may help enrich the understanding of the complex behavior of the shear strength of the pile–soil interface for energy piles and related soil–structure interaction.