Effect of one cycle of heating-cooling on the clay-concrete pile interface shear strength parameters

Abstract

This study investigated the effect of applying a one heating-cooling cycle on the interface strength parameters of saturated clay soil in contact with concrete, and the potential use of heating to improve/increase the pile capacity. 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 soil-concrete interface tests. A concrete block was built and placed in the bottom section of the shear device. Heating rods system were used to heat the circulating water that heated the specimens. The experimental tests were conducted on low plasticity soil with PI = 12, medium plasticity soil with PI = 29, and high plasticity soil with PI = 60. The specimens were first consolidated to a target normal stress prior to shearing. Two tests were performed for each normal stress and clay type with one test performed without heating-cooling cycle at ∼20 °C and the other test performed at ∼20 °C after a heating-cooling cycle up to 70 °C. The specimens were tested under different normal stresses ranging from 30 to 150 kPa. The specimens' temperature was increased gradually during the heating process from room temperature (∼20 °C) to ∼70 °C. The specimens were then gradually cooled back to room temperature. The test results showed significant increase in both the peak and residual interface friction angles by a percent ranges from 13.6% to 35.5%. The specimens subjected to a one heating-cooling cycle during shear experienced significant volumetric reduction by a percent ranges from 11.3% to 96%. The thermally induced “contraction” volumetric strain (TIVS) was found to increase with increasing temperature loading and the plasticity index, PI, but independent of the applied normal stress.