Centrifuge investigation on the inclination of 2×2 energy pile group subjected to non-symmetrical cyclic thermal loading

During the operation of energy pile-based ground source heat pump systems, the energy piles can experience non-symmetrical temperature changes, resulting in pile group inclination. This can affect its serviceability unfavourably. By conducting centrifuge tests, this study quantified the inclination of 2×2 energy pile groups in sand induced by non-symmetrical cyclic thermal loading. During each test, 15 two-way thermal cycles with an amplitude of 10 ?C were applied while maintaining a constant vertical load. A total of 10 tests were carried out to evaluate the effects of energy pile distribution within the group, magnitude of vertical load, and raft-soil interaction on the pile group inclination. The results showed that the pile group inclination accumulated with thermal cycles at a reducing rate. Under normal vertical load (FoS = 2.0), the accumulated inclination was about 1.8‰, less than 2.5‰ as specified by the design code. Axial load redistribution occurred with a maximum increase of about 40% of the initial value. As the vertical load increased, the accumulated inclination could exceed 2.5‰. The pile group inclination induced by non-symmetrical cyclic thermal loading should be well considered at the design stage.