Experimental study on thermo-mechanical responses of pre-bored grouted planted piles with different restraint conditions.

Geothermal energy piles (GEPs) are an innovation technology of vertical ground heat exchangers (GHXs) which can be used for the heating and cooling of building combined with ground source heat pumps. The main barriers to adoption are the inconvenient installation and a lack of the knowledge regarding the potential effect of temperature changes on pile foundations compared to traditional GHXs. The installation process can be facilitated by using pre-bored grouted planted (PGP) GEPs, which simplify the installation of heat exchange pipes and hence reduce the installation time. It is desirable to investigate the thermo-mechanical responses of this GEP for understanding the potential effects of the temperature changes. A PGP GEP was installed in a building during construction that incorporated two heating tests with different conditions (a short-term Test 1 without building load, and a long-term Test 2 with strong structural restraints and building load) to investigate the behavior of the PGP GEP. A fiber Bragg grating (FBG) sensor system was used to evaluate temperature and strain behaviors of the test pile and two adjacent boreholes. The results show that the nonuniform spatio-temporal response of temperature induced the nonuniform thermal-induced stress along the pile depth. The end-restraints had significant effects on the thermo-mechanical response over the full pile. A comparison between the PGP GEP and other types of GEPs were conducted, and the similarities and differences between them were discussed. [ABSTRACT FROM AUTHOR]