Numerical and experimental effect of heating and cooling cycles on the skin friction of energy piles in soft clays -

Abstract

Because of the current environmental problems, our planet is poised at the brink of a severe environmental crisis. This deviated the attention towards renewable energy, in particular, geothermal energy. In addition, with the increase of the use of deep foundation, integrating piles with geothermal systems became a trend. Although energy pile systems have been successfully used in the world, there are no clear design guides providing how thermal actions are considered in terms of safety and serviceability of energy piles (Bourne-Webb et al. 20161). The primary function of energy piles is to safely carry loads while minimizing unacceptable movement or damage to the structure itself. A concern that arises from the use of structures with energy piles centers around the need to account for the possibility that the secondary use of the piles as heat exchangers could negatively affect the ability of the pile to carry the design load. The shear strength of the interface defines the stability of the pile and the thermo-hydro-mechanical changes, resulting from thermal cycles, affects the behavior of the interface at the saturated soil- pile level. Published work on energy piles shows that in granular and very stiff, moderately to highly overconsolidated clayey soils, thermal effects on the mechanical properties of the soils may be neglected. However, heating may induce flow of water around the pile and could affect the skin friction and the adhesion between the pile and the surrounding soil. This issue has not been fully investigated in the literature. In this research, two small-scaled models were adopted to inspect this gap. These models aimed to study the effect of the thermal loading on the frictional capacity of the energy piles in saturated slightly overconsolidated clays with and without sustained static uplift load that is roughly 30percent of the ultimate capacity. Results indicated that the ultimate capacity decreased compared to the control pile by observing a reduction in the adhesion factor in the order of 11 to