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Numerical study of the response of a group of energy piles under different combinations of thermo-mechanical loads
No full textEnergy piles are rapidly gaining acceptance around the world because they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings, and the de-icing of infrastructures. This technology couples the structural role of pile foundations with an energy supply using the principle of shallow geothermal energy. The exploitation of geothermal energy represents an additional thermal load that is imposed to the foundation and the surrounding soil. Because the primary role of energy piles is the stability of the overlying structure, this aspect must be ensured even in the presence of the additional thermal load. This study summarises the results of 3-D thermo-hydro-mechanical finite element analyses that investigated the behaviour of a group of energy piles for which field data were available. This allowed the nearly unique validation of the numerical approach with experimental data and a confirmation of the reliability of the results. The work provides a summary of the foundation behaviour under both conventional and extreme thermal loading conditions with reference to a geothermal operation of the piles for cooling and/or thermal energy storage applications within one season. The interaction between the piles is studied and the thermally induced group effects analysed. Attention is dedicated to the vertical stress and displacement developments in the piles. The results presented in this study outline crucial aspects that may be considered by engineers for the geotechnical and structural designs of such geostructure
Energy and geotechnical behaviour of energy piles for different design solutions
Get PDFEnergy piles are heat capacity systems that have been increasingly exploited to provide both supplies of energy and structural support to civil structures. The energy and geotechnical behaviours of such foundations, which are governed by their response to thermo-mechanical loads, is currently not fully understood, especially considering the different design solutions for ground-coupled heat exchangers. This paper summarises the results of numerical sensitivity analyses that were performed to investigate the thermo-mechanical response of a full-scale energy pile for different (i) pipe configurations, (ii) foundation aspect ratios, (iii) mass flow rates of the fluid circulating in the pipes and (iv) fluid mixture compositions. This study outlines the impacts of the different solutions on the energy and geotechnical behaviour of the energy piles along with important forethoughts that engineers might consider in the design of such foundations. It was observed that the pipe configuration strongly influenced both the energy and the geotechnical performance of the energy piles. The foundation aspect ratio also played an important role in this context. The mass flow rate of the fluid circulating in the pipes remarkably influenced only the energy performance of the foundation. Usual mixtures of a water-antifreeze liquid circulating in the pipes did not markedly affect both the energy and the geotechnical performance of the pile
Group action effects caused by various operating energy piles
No full textTo date, no field data referring to various operating energy piles over time-scales of practical applications had been made available to investigate the thermally induced “group action”. This paper presents the results of a full-scale field test and a three-dimensional thermo-mechanical finite element analysis of four operating energy piles over 12 months. When the number of operating energy piles increases, greater thermally induced vertical strain and lower stress develop along the piles for the same average temperature change. Opposite stress variations to those that may be expected based on the type of applied thermal load can develop in piles.LM
Analysis of thermally induced mechanical interactions in energy pile groups
No full textThis study investigates the thermally induced mechanical interactions among closely spaced energy piles that partially operate as geothermal heat exchangers over a time-scale that is typical of practical applications. The analysis is based on the results of a full-scale in-situ test of a group of energy piles and a coupled 3-D thermo-mechanical finite element analysis. The work highlights two types of thermally induced mechanical interactions in energy pile groups, i.e., first- and second-kind interactions. The former interactions develop during early stages of geothermal operations of energy piles. The latter interactions develop during successive stages of geothermal operations of energy piles. The impact of these interactions on the variation of the mechanical behaviour of energy pile groups varies with time. Attention must be devoted to these interactions throughout the design process (e.g., geotechnical and structural) of energy piles because they play an important role in the serviceability performance of these foundations.LM
Geotechnical analysis of energy piles
No full textThis study proposes an analysis of the multiphysical phenomena and mechanisms governing the thermo-mechanical behaviour of energy piles. The analysis is based on the results of a series of full-scale in-situ tests, laboratory experiments and numerical analyses. First, the thermo-mechanical behaviour of energy piles is considered. Attention is given to both single and groups of energy piles. Next, the response of soils and concrete-soil interfaces subjected to temperature changes is reviewed. The behaviours of clayey soils in different overconsolidation states as well as of both concrete-sand and concrete-clay interfaces are analysed. Finally, aspects considered of paramount importance for the analysis and design (e.g., geotechnical and structural) of energy piles are presented. Both floating and end-bearing energy piles are investigated. The goal of this paper is to increase the confidence of civil engineers on the performance of energy piles.LM
The interaction factor method for energy pile groups
Get PDFPrior to this study, no simplified yet rational methods were available for estimating the vertical displacements of energy pile groups subjected to thermal loads. Observing such a challenge, the goal of this study has been threefold: (i) to extend the interaction factor concept from the framework of conventional pile groups to that of energy pile groups, (ii) to present charts for the analysis of the displacement interaction between two identical energy piles over a broad range of design conditions, and (iii) to propose, apply and validate the interaction factor method for the displacement analysis of energy pile groups.LM
Recent development in the multiphysical analysis and design of energy piles
No full textThis study proposes an analysis of the multiphysical phenomena governing the thermo-mechanical behaviour of energy piles. The analysis is based on the results of a series of full-scale in-situ tests, laboratory experiments and numerical analyses. First, the thermo-mechanical behaviour of energy piles is considered. Attention is given to both single and groups of energy piles. Next, the response of soils and concrete-soil interfaces subjected to temperature changes is reviewed. The behaviours of clayey soils in different overconsolidation states as well as of both concrete-sand and concrete-clay interfaces are analysed. Finally, aspects considered of paramount importance for the analysis and design (e.g., geotechnical and structural) of energy piles are presented. Both floating and end-bearing energy piles are investigated. The goal of this paper is to increase the confidence of civil engineers on the performance of energy piles.LM
The role of thermally induced soil deformation on the serviceability of energy piles
No full textThis paper investigates the impact of the thermally induced deformation of soil on the serviceability mechanical performance (i.e., deformation-related) of energy pile groups. The work is based on the results of a full-scale in-situ test that was performed over a typical time-scale of practical applications on a group of energy piles at the Swiss Tech Convention Centre, Lausanne, Switzerland, and on a series of 3-D thermo-mechanical finite element analyses that were carried out to predict the considered experiment. This study proves that the serviceability mechanical performance of energy pile groups crucially depends on the thermally induced deformation of soil. Considering this aspect in the analysis and design of energy piles is important because it profoundly characterizes the deformation of such foundations.LM
Numerical study on the thermo-mechanical interactions of a group of energy piles under cooling loads
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