Field tests on thermal response characteristics of micro steel pile group under multiple temperature cycles in winter conditions

The energy pile technology has dual functions of supporting superstructure and acting as shallow geothermal heat exchanger. As an energy-saving and emission-reduction technology, it has obtained certain development in recent years. Relying on the micro steel piles to reinforce the existing foundation underpinning project, the field tests on thermal response of the micro steel group piles under multiple temperature cycles are carried out. The variation of pile temperature and pile stress under different intermittent time is measured. The coefficients of performance (C_OP) of piles are discussed and analyzed. It is shown that the additional thermal stress of piles increases with the increasing cycling times, and the increase ratio decreases with the interval time; the C_OP of piles decreases with the increasing cycling times, and the decrease ratio decreases with the interval time. The values of the additional tensile stress does not exceed the design control range, which will not cause the damage of the pile.