Abstract: Energy pile is a new technology which supports the upper building load and extracts geothermal energy from its surrounding simultaneously. However, there is only little research available on the thermal-mechanical behavior of the piles subject to heating-cooling cycles and particularly repeated cycles. Model tests are carried out to examine the heat transfer performance and bearing characteristics of energy pile with embedded steel tube under working loading conditions over repeated temperature cycling, and especially the law of pile head displacement. Moreover, the displacement is also observed and analyzed under no load over one cycle of heating and cooling for comparative analysis. The results show that the heating-cooling cycles produce thermal strain in the pile shaft, heating generates compressive stress and cooling induces the tensile stress. Meanwhile, the positive and negative frictions are yielded in different parts of the pile side due to temperature. The upward displacement magnitude of pile top under no working load is 41% greater than that under working load, but the final displacement of pile top is approximately 10% of that under working load after one heating-cooling cycle. The repeated temperature cycling can lead to continuous accumulation of settlement.

Key words: pile foundation, energy pile, embedded steel tube, thermal mechanical behavior, model test