Group performance of multiple series-connected energy piles under thermal loading

Thermomechanical behaviors of energy piles in rows, which are connected by a branch or branches, are investigated through a series of in-situ field tests. Thermally induced group effect influenced by thermal interference was measured and discussed. The interaction factor was extended to reflect the group effect of the pile branches which had differential head displace-ments. Results indicated that the heat exchange efficiency and thermal expansion coefficients were reduced, while the degree of freedom and pile head displacement were enlarged with the thermal interference. The pile temperatures, thermally induced stresses, and head displacement are decreased linearly with the direction of the flowing water. The heat exchange efficiency of the thermally affected branch was 93.6% and 91.8% of that of the isolated branch (1 x 3) as the thermal interference was on one side (2 x 3) and both sides (3 x 3), respectively. Additionally, the thermal interference of one adding pile branch caused the maximum thermally induced stress of the pile in the adjacent branch to increase by 49.0%, which is-1.46 MPa. The interaction factor on the branch effected by both-side thermal interference is 52.7%, which is about five times that of the branch effected by one-side thermal interference (10.6%).