  Soil structure interaction in energy piles has not yet been understood
comprehensively. One of the important underlying issues is the location of a
zero-displacement point, known as the null point. This study investigates how
the location of a combined null point in fully floating energy piles is
affected by relative magnitudes of thermal and mechanical loads. Analytical
solutions are used to address four different loading scenarios including
compressive and tensile loads, and heating and cooling. It was found that the
location of the combined null point coincides with the location of the maximum
magnitude of the axial stress induced by thermo-mechanical load. Furthermore,
while a thermal null point is always present in fully floating energy piles,
the combined null point is absent in the case of a small magnitude of thermal
load as compared to the mechanical load. With increase in the relative
magnitude of thermal load as compared to the mechanical load the combined null
point emerges at different locations for different load combinations. In all
cases it subsequently moves towards the mid-length of the pile with increase in
the relative magnitude of thermal load.
