Abstract
Energy piles are foundation elements having the double scope of transferring structural loads from the structure to the ground and of exchanging heat with the surrounding soil. It follows that pile state of stress and settlement are altered by the time-dependent temperature change in both pile and soil. This work is aimed at investigating the effect of thermal cycles on the behaviour of a single energy pile. To this end, fully coupled thermo-hydro-mechanical analyses have been carried out using the Finite Element code ABAQUS. The single pile is installed in a normally consolidated clay behaving according to different constitutive models involving Mohr-Coulomb, Modified Cam Clay and Hypoplastic. The latter is employed with and without the thermal formulation capable of accounting for the thermal collapse of NC clays during heating. A single free-head pile is considered and the results are presented in terms of pile axial force and settlement developed cycle by cycle.
Highlights
Results of laboratory tests on soil specimens have proven that normally consolidated and slightly overconsolidated clays experience volumetric contraction when heated in drained conditions [1,2,3,4,5,6,7], and this certainly affects the behaviour of a pile embedded in this soil
In the FE analyses, the soil behaviour is modelled employing different constitutive models, i.e. the MohrCoulomb (MC), the Modified Cam-Clay (MCC), and the Hypoplastic model with and without the thermal formulation (Hypo and Hypo-T, respectively) The classical elasto-plastic models are developed in the framework of the perfect or hardening plasticity theory and are not capable of properly describing the accumulation of irreversible strain and pore water pressures caused by the cyclic thermal loading
The scope of the study presented is to investigate the cyclic performance of a single energy pile embedded in NC clay
Summary
Results of laboratory tests on soil specimens have proven that normally consolidated and slightly overconsolidated clays experience volumetric contraction when heated in drained conditions [1,2,3,4,5,6,7], and this certainly affects the behaviour of a pile embedded in this soil. To investigate the effects of the thermal cycles on the global performance of a single energy pile embedded in NC clay and subjected to mechanical and cyclic thermal loads, fully coupled thermo-hydro-mechanical analyses have been carried out. In the FE analyses, the soil behaviour is modelled employing different constitutive models, i.e. the MohrCoulomb (MC), the Modified Cam-Clay (MCC), and the Hypoplastic model with and without the thermal formulation (Hypo and Hypo-T, respectively) The classical elasto-plastic models are developed in the framework of the perfect or hardening plasticity theory and are not capable of properly describing the accumulation of irreversible strain and pore water pressures caused by the cyclic thermal loading. Hypoplastic model may include the thermal formulation capable of reproducing the thermal collapse of the NC clay [12, 13]
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