Performance of a Belled Pile Influenced by Pile Head Freedom Response to a Cooling-Heating Cycle

This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling-heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of -2.8x10(-5)/kN. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to incremental floors, and an elastic recoverable characteristic response to cooling-heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions. (C) 2022 American Society of Civil Engineers.