Centrifuge Modeling of Cyclic Nonsymmetrical Thermally Loaded Energy Pile Groups in Clay

Heat transfer from/to energy piles can cause plastic contraction of soft clay with a low overconsolidation ratio (OCR) during heating and cooling. This can lead to thermally induced excess pore water pressure and changes in the lateral stress acting on a pile. These thermally induced phenomena cause additional plastic settlement of the soil and pile. Irreversible settlement may cause serviceability or ultimate limit state problems for floating energy piles whose capacity is mainly derived from shaft resistance. Due to intended operational needs or by accident, cyclic nonsymmetrical thermal loads may be applied to floating energy pile groups and piled rafts. The thermomechanical interaction among nonsymmetrical loaded piles is not well understood. In this study, a series of cyclic nonsymmetrical thermally loaded centrifuge model tests were conducted on floating pile groups and piled rafts in soft kaolin clay with an OCR of 1.7 at the pile toe. The performance of floating 2x2 elevated energy pile groups and energy piled rafts was investigated. Three piles in each group were subjected to 15 cycles of +/- 14 degrees C in temperature change. The thermally induced irreversible settlement and tilting of the elevated pile groups exceeded serviceability and ultimate criteria. The piled rafts similarly settled but to a smaller extent than the elevated group. Their tilting, however, did not exceed the serviceability criterion. It is recommended that energy piled rafts be used in soft clay instead of elevated energy piles. (c) 2021 American Society of Civil Engineers.

Automated summary

The study found that thermally induced irreversible settlement and tilting of floating energy piles in soft clay may exceed serviceability and ultimate criteria, recommending the use of energy piled rafts instead of elevated piles in soft clay.