Experimental and numerical investigations of thermo-mechanical behaviour of energy pile under cyclic temperature loads

Thermo-mechanical behaviour of energy pile under cyclic temperature load is vital for its safe and efficient operation. In this work, a model test device with reduced size was established to find the thermo-mechanical behaviour of energy pile subjected to different cyclic temperature loads. The test results suggest that the thermo-mechanical performance of energy pile operated in the winter and summer modes is greatly affected by the cycle days.The temperature change of pile and soil will gradually accumulate with the increase of circle days, the daily heat exchange amount of energy pile and soil temperature recovery rate will decrease, and the changes of pile mechanical properties such as pile top displacement, pile thermal strain, and soil pressure will also increase. A 3-D mathematical model of energy pile is established to further obtain the effects of various factors on the thermo-mechanical behaviour of energy pile with cyclic temperature loads. It can be found that the cooling and heating cycles of energy pile with different pile top building loads will lead to additional pile top settlement, and the larger the pile top building load, the larger the additional pile top settlement. Under the same operating time, the more the continuous heat release or heat absorption, the larger the fluctuation range of pile body temperature, the larger the residual temperature of pile body, which will result in a larger pile top and radial displacement. As for the soil type, the heat exchange rate per unit pile depth in summer mode is the largest in the rock, followed by the sand and clay, and the corresponding values in winter mode is the smallest in the rock, followed by the sand and clay. At the same time, the pile top displacement in rock is the smallest, followed by clay and sand. The fluctuation range of pile radial displacement is the largest in clay, followed by sand and rock.