EXPERIMENTAL STUDY ON THERMO-MECHANICAL PROPERTIES OF ENERGY PILES UNDER ACTION OF CYCLIC TEMPERATURE

Energy piles are combinations of pile foundations and ground source heat pumps. They not only bear the upper building load but also act as media for heat exchange with the shallow geothermal energy, which are of advantage on energy-saving and pollution reduction. Based on indoor model tests, the displacement of pile tops, pile bottom pressure, temperature stress and side friction resistance of energy piles in clay foundation under the action of cyclic temperature were experimentally studied. It was concluded that the rise or fall in temperature could also cause tensile and compressive stress in piles, stress increased first and then decreased in pile shafts from tops to bottoms of piles, and the maximum stress was close to the lower middle parts of piles. The compressive stress of pile bottoms increased with the increase of temperature, and the maximum compressive stress decreased with the increase of temperature cycles. Friction resistance of pile sides increased with the increase of temperature. During the period of being heated and cooled, and the negative friction resistance would be generated on upper parts and lower parts of piles respectively.