Influence of pile head restraint on the performance of floating elevated energy pile groups in soft clay

Thermal elongation of energy piles (EPs) depends on the end restraints to displacement. The EP head is restrained by a working load and non-energy piles (NEPs) within an energy pile group, depending on the cap rigidity. The existence of both EPs and NEPs in non-symmetrical thermally loaded energy pile groups imposes different restraints on EP heads, resulting in different pile elongations. This would induce load redistribution between the piles, thereby influencing the serviceability of energy pile groups in soft soil. In this paper, a 3-D numerical parametric study was conducted after back-analysing a centrifuge test on a floating elevated energy pile group subjected to cyclic non-symmetrical thermal loading in soft clay. Effects of the number of EPs and NEPs in a 2 x 2 group, the flexural stiffness of the cap, and the factor of safety (FS; i.e., working load level) were studied. The non-symmetrical thermally loaded pile group with 3EPs and a rigid cap subjected to the lowest FS showed the maximum settlement due to the largest thermomechanical loading distributed between the piles through the rigid cap. In contrast, a flexible cap over the 2EPs group induced the maximum tilting due to a closer distance between EPs and NEPs in a side tilting. The axial load reduction was significant mainly in the 1EP group during cooling and at a higher FS, resulting in tension along the EP, which should be considered in the design.