Continuum Analytical Models for the Ultimate Limit State Design of Energy Piles

Energy piles are foundation elements having the double role of transferring structural loads and exchanging heat with the surrounding soil for heating and cooling of buildings. Because of the restraining action exerted by the soil, the temperature variation of piles leads to stresses that combine with those resulting from mechanical loads. The proposed work presents a continuum analytical model for the evaluation of the thermally induced axial force developing as a consequence of the thermal interaction between the pile and the surrounding soil. Solutions are derived for end-bearing piles installed in a homogeneous soil and in a soil deposit with linearly increasing stiffness with depth. The results obtained with the proposed formulae are compared with exact Winkler-based analytical solutions already available in literature as well as with more complex numerical analyses, proving to be a simple and effective tool for the ultimate limit state design of energy piles.