Behaviours of a belled energy pile under heating-cooling cycles

This paper presents a field test investigation on the behaviours of a belled energy pile after three heating-cooling cycles (3-35 degrees C). The belled energy pile (D = 1.2 m, L = 14.0 m) was under an 8-story building with a one-floor basement, and the expanded foot at the pile toe was 2.0 m in height and 1.2-3.2 m in diameter. Residual strains, stresses and settlements developed during the thermal cycles, even when the temperature was fully recovered. The decrease in shaft friction at the lower part of the belled energy pile was higher than that of the straight pile, and near-zero shaft friction at the lower part of the pile was observed at the end of the second and third thermal cycles. The expanded foot was also found to enhance the end restraint condition of the belled pile. The degrees of freedom near the bottom of the belled energy pile were 0.11 and 0.32 during pile heating and cooling, respectively; these were lower than those of the straight pile. The settlement of the belled energy pile after three cycles was 0.17 parts per thousand D (0.21 mm) and was lower than that of the straight energy pile.