Centrifuge modelling of inclination of 2×2 energy pile groups subjected to non-symmetrical cyclic thermal loading

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