The effect of cyclic temperature variation on pile foundations used as heat exchangers

cyclic_tempThe incorporation of heat exchangers, for ground source heating and cooling, into pile foundations is becoming increasingly prevalent within the construction industry. Using pile foundations as heat exchangers has the ability to reduce a buildings carbon emissions produced through space heating and cooling, along with hot water production. However, there is limited work to date detailing the effects of thermal cycles on the mobilisable clay strength, with most designs opting for conservative approaches.

This project seeks to develop laboratory test apparatus for the investigation of clay strength at elevated temperatures after multiple thermal cycles, simulating ground source cooling, to determine if current design standards are appropriate.

For this study, a thermally controlled triaxial apparatus was designed and operated at the University of Sheffield. This will then used to control both stress and temperature simultaneously, in order to simulate effects similar to those in the field surrounding thermal pile foundations. Clays of different plasticities are to be tested, monitoring their volume changes throughout temperature cycles and determining the effect of temperature cycles on the ultimate shear strength and stiffness of the clay sample.