Implications of Thermal Cyclic Loading on Pile Group Behavior

This study investigated the thermomechanical behavior of thermal pile groups in sand. To analyze the influence of cyclic thermal loading on the stress–strain behavior of piles in a group, pile groups containing four thermal piles installed in dense Toyoura sand were numerically investigated. A concrete pile cap was considered on the piles. Axial mechanical load was applied instantaneously on the pile cap and thermal load was applied along the pile length for six thermal cycles consisting of alternate heating and cooling of the piles. The concrete piles and pile cap were considered to behave in a linear-elastic manner under the mechanical load and thermal load. The soil was assumed to possess elastoplastic behavior and was simulated using the Mohr–Coulomb plasticity model. The effect of mechanical and cyclic thermal load on the pile groups was studied by varying the pile group parameters such as pile spacing ($s_p$), pile diameter ($D_p$), and thickness of the pile cap ($t_{\mathit{pc}}$). In all the analyses, the effect of cyclic thermal load was compared in terms of development of axial displacement, axial strains, and axial stresses in the piles. Thermomechanically loaded piles exhibited higher displacements, strains and stresses than did mechanically loaded piles. The results also indicate that the axial load on the piles under cyclic thermal loading was larger for the piles with higher aspect ratio than for the piles with lower aspect ratio. The effect of pile spacing was more pronounced in case of piles with higher aspect ratio. An increased thickness of the pile cap resulted in higher axial load and displacement in the piles. The cyclic thermal load resulted in residual or plastic strains in the piles. The thermomechanical behavior of a pile group is influenced by parameters such as pile spacing, aspect ratio, and pile cap thickness, which should be considered in thermal pile group design for structural stability performance of the pile group.