Effect of one cycle of heating-cooling on the clay-concrete pile interface behavior

This study investigated the effect of applying one heating-cooling cycle on the interface strength parameters of saturated clay soil-concrete, and the potential use of the heating process to improve the side capacity of piles driven in clayey soil. A large direct shear test device with inner dimensions of 300 mm, 300 mm, and 200 mm for width, length, and height, respectively was modified to perform the interface soil-concrete tests. A concrete block (300 mm × 300 mm × 100 mm) was built and placed at the bottom section of the shear device. Watlaw heating fire rods system was used to heat the circulating water that heat the specimens. The experimental tests were conducted on Low Plasticity Index soil with PI=12. The specimens were first consolidated to a target normal stress prior to shearing. Two specimens at different testing temperature (room temperature = 20 °C, 70 °C) were tested for each of the four different normal stresses (30, 69, 110, and 150 kPa). The temperature for the heated specimens was increased gradually during the heating process from the room temperature (20 °C ± 2 °C) to 70 °C ± 2 °C in 3 hours. The specimens were then cooled back to room temperature. The test results showed significant increase in both peak and residual interface shear strength parameters by 13.6% and 15.6% increase in friction angle, respectively. Also, volumetric strain under shearing decreased after the heating and cooling cycle by 30.0%, 24.4%, 11.3%, and 24.2% under 30 kPa, 69 kPa, 110 kPa, and 150 kPa, respectively.