ABSTRACT
Although energy geostructures, and among them thermoactive piles, have been in use for almost 50 years, design offices and decision makers are still reluctant to routinely integrate this technique in the final design solutions, as some unresolved technical issues appear to remain, as well as comprehensive guidelines based on in situ tests and projects feedback. Indeed, one of the remaining issues is the potential effect of temperature and more importantly of the accumulation of heating-cooling cycles on the soil-pile interface and therefore on the long-term behaviour of a pile, as well as on its bearing capacity. With the ever increasing cost of fossil energy, and the need to propose green solutions limiting global warming and its consequences, it is of the upmost importance to address these issues. To do so, five thermoactive continuous flight auger piles were thus constructed on two different sites (one mostly sandy and the other mostly made of clay and marls). They were mechanically loaded at different levels ranging from the quasi-permanent Serviceability Limit State (SLS) to the characteristic SLS, and submitted to multiple thermal cycles. They were then loaded to the failure, to assess the impact of these cycles on the bearing capacity. The embedded instrumentation (fiber optic, strain gauges, etc.) allowed estimating the distribution of the load along the shafts, and the possible effect of the repeated thermal loadings on the shaft and base resistances. This paper shows that the bearing capacity of piles executed in fine soils does not seem to be affected by temperature cycles, while that of piles executed in sandy soils shows a noticeable increase.
