Behavior of a dual-purpose pile as foundation and heat exchanger [Comportement d'un pieu bi-fonction, fondation et échangeur de chaleur]

The behaviour of a pile subjected to thermo-mechanical loads was studied in situ with the aim of quantifying the thermal influence on the bearing capacity of heat exchanger piles. To accomplish this, a pile situated in a building under construction was equipped with a pipe system to inject heat into it using a special heat pump. Load cells, deformation gauges, and thermometers were installed to evaluate the behaviour of the pile during seven tests with coupled thermo-mechanical loads. The temperature variations applied to the pile were of the order of 15degreesC and the mechanical load reached 1300 kN. The results permitted the quantification of three significant effects brought about by the temperature increase: (i) pile uplift, (ii) mobilization of skin friction due to the relative displacement of the pile with respect to the ground, (iii) additional load generated in the pile by constrained dilation.