Providing low carbon cooling through pile foundations; the effect of thermal cycling on clay strength

Abstract

Pile foundations provide a low-intrusive mechanism for installing heat exchangers into the ground, especially if the piles are being installed to support the building. The ground temperature is relatively constant at depths >10 m, providing consistent performance of the heat exchanger to the operator. However, as these piles are also being used to support the building above, a greater understanding of clay's response to temperature must be further identified to allow confidence in their installation. A review of case studies, field tests and laboratory tests illustrates the need for further work in ths area. This paper reports initial results from a series of specialized tests on two types of clay subjected to five thermal cycles, representing the long-term operation of pile foundation heat exchangers, and shows that distinct shrink/swell cycles occur leading to ~5% reduction in volume over the five cycles for a kaolin clay and 0.5% for a glacial till..