Experimental study on structural response of CFG energy piles

Abstract Energy piles have gradually emerged as a new application of ground source heat pump systems due to the heat exchange efficiency per unit length, excellent heat conductivity and low construction cost. Full-scale field tests are carried out to study the thermo-mechanical behavior of “Cement Fly-ash Gravel (CFG) piles”, a popular ground improvement technology in China. These piles are actually constructed by continuous flight auger (CFA) with the cement, fly ash, gravel, etc., being the constituents of the concrete used to form the pile shaft. The displacement of the pile head is measured, thermal stress due to temperature change of the pile is calculated and the changing laws of the stress/strain and temperature profiles along the depth of the pile under thermal loads and constant mechanical loads applied on pile head are analyzed. An ultimate bearing capacity test of a single CFG pile/soil composite foundation is carried out to investigate the effects of the heating–cooling exchange process on the bearing capacity of CFG energy piles. Systematic tests are implemented to study the mechanical responses of CFG energy piles and the effects of thermal stress on the mechanical behavior of the piles, which will benefit the design and application of CFG energy piles.

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