Thermo-mechanics behaviour of energy pile subjected by monotonic thermal loading

Cet article passe en revue le développement des pieux géothermiques intégrés dans la conception de bâtiments. Il présente le processus physique de transfert de chaleur et l'observation du comportement mécanique des pieux à l'aide de modèles numériques basés sur la méthode des différences finies (FLAC3D). Un modèle préliminaire a été étudié, portant sur la diffusion de la chaleur en régime permanent dans un pieu isolé. Il est constaté que le pieu est en contraction pendant le mode de réchauffement (en hiver) et en dilatation pendant le mode de refroidissement (en été)

Thermal Behaviour under Service Loads of a Thermo-Active Precast Pile

[EN] A research project was developed in Spain to undertake some studies on the geothermal use of pile foundations (PITERM PROJECT). The experiment consists of a specifically designed, constructed and fully monitored geothermal precast pile driven at Polytechnic University of Valencia. An important distinctive feature of the developed pile was the fact that it was assembled from two identical sections connected with a specific joint, developed by Rodio-Kronsa. This allows the installation of much longer precast piles into the ground. The pile is under two types of loads: mechanical and thermal. The mechanical load was applied by means of a mechanical frame anchored to the ground and three additional anchors used to induce an active compressive force. The thermal load was produced by means of a thermal rig able to inject heat or extract heat from the pile at any desired programable heat injection/extraction rate. One of the features of this precast pile is its geometry, similar to a single U borehole heat exchanger (BHE) which is not common in thermoactive piles, usually equipped with probes attached to the armatures. In our study, we have characterized the thermal behaviour of the precast pile experimentally and simulated its temperature response by means of a TRNSYS model. This article describes part of a test series carried out where the mechanical and thermal behaviour of a pile subjected to thermal and mechanical loads simulating a real pile in a building was studied. Therefore, this publication has only focused on the thermal performance of the pile and its thermal modelling by computer. From this model, the thermal parameters of the soil¿pile system have been extracted and compared with those of a single standard single U BHE. In essence, our assessment points to a quite similar thermal behaviour of the studied precast pile compared to a conventional single U borehole heat exchanger of the same length and equivalent diameter, while the installation costs of such elements would be substantially lower due to its double, structural and thermal, function.We thank the Spanish Ministry of Economy and Competitiveness for its financial support, through the program INNPACTO 2011 (IPT-2011-1214-380000), for the design, installation and instrumentation of the geothermal pile in Valencia. We thank Rodio Kronsa, CEDEX and Energesis for their dedication and participation in the project.Badenes Badenes, B.; Magraner Benedicto, MT.; De Santiago, C.; Pardo, F.; Urchueguía Schölzel, JF. (2017). Thermal Behaviour under Service Loads of a Thermo-Active Precast Pile. Energies. 10(9). https://doi.org/10.3390/en10091315S109Olgun, C. G., Ozudogru, T. Y., Abdelaziz, S. L., & Senol, A. (2014). Long-term performance of heat exchanger piles. Acta Geotechnica, 10(5), 553-569. doi:10.1007/s11440-014-0334-zMurphy, K. D., McCartney, J. S., & Henry, K. S. (2014). Evaluation of thermo-mechanical and thermal behavior of full-scale energy foundations. Acta Geotechnica, 10(2), 179-195. doi:10.1007/s11440-013-0298-4Abdelaziz, S. L., & Ozudogru, T. Y. (2016). Selection of the design temperature change for energy piles. Applied Thermal Engineering, 107, 1036-1045. doi:10.1016/j.applthermaleng.2016.07.067Magraner, T., Montero, Á., Quilis, S., & Urchueguía, J. F. (2010). Comparison between design and actual energy performance of a HVAC-ground coupled heat pump system in cooling and heating operation. Energy and Buildings, 42(9), 1394-1401. doi:10.1016/j.enbuild.2010.03.00

Analysis and design methods for energy geostructures

Based on discussions at the international workshop on “Thermoactive geotechnical systems for near-surface geothermal energy”, hosted at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland (http://www.olgun.cee.vt.edu/workshop/), this article attempts to provide a broad overview of the analysis methods used for evaluation of systems that use either boreholes or geo-structures for heat exchange. It identifies commonalities where knowledge transfer from the former to the latter can be made, and highlights where there are significant differences that may limit this cross-fertilisation. The article then focusses on recent developments and current understanding pertaining to the analysis of the thermo-mechanical interaction between a geostructure and the ground, and how this may be incorporated into the geotechnical design of energy geostructures

3D transient heat transfer numerical analysis of multiple energy piles

This paper presents a three-dimensional (3D) transient heat transfer numerical model for multiple energy piles based on the finite volume method (FVM). The initial and boundary conditions are established and the effects of “thermal short-circulating” between two pipes of a U-tube in energy pile are investigated. Thermal partial differential equations are discretized at the spatial nodal points and solved by linear approximation method. Temperature variations of working fluid, energy pile and its surrounding soil from simulation program are compared with experimental data to validate the developed model. In addition, the influences of fluid flow rate and U-tube shank spacing are analysed. It is established that the shank spacing should be set in a range of 0.06m to 0.10m to reduce heat transfer between the two pipes and meet the structural requirement. Meanwhile, the flow rate should be controlled in a range of 0.5m3/h to 0.7m3/h to avoid the low outlet fluid temperature and decrease the influence of “thermal short-circuiting”

Étude numérique du comportement des pieux énergétiques dans les sols granulaires

Les pieux énergétiques constituent une technique récente permettant d’une part le chauffage et la climatisation de bâtiments et assurant d’autre part le rôle de fondations profondes. Cette technique consiste à mettre en place dans des fondations profondes classiques un système échangeur de chaleur. Le principe de transfert de chaleur est similaire à celui utilisé pour des systèmes échangeurs de chaleur conventionnels : un fluide caloporteur permet d’extraire de l’énergie thermique du sol durant l'hiver et d’en injecter durant l’été. Dans le cas de pieux énergétiques, l’interaction entre le sol, le pieu et la structure ne fait pas seulement appel à des considérations mécaniques mais exigent de tenir compte d’aspects thermiques et hydrauliques, ce qui rend relativement complexe la compréhension globale du comportement d’un pieu énergétique. Actuellement, en France, la réalisation effective de pieux énergétiques rencontre un certain nombre de difficultés qui sont en partie liées à une connaissance insuffisante des effets des cycles de température sur la pérennité d’un système de fondations constitué de pieux échangeurs de chaleur. L’objectif de ce mémoire est d’apporter quelques éclairages sur ce sujet, notamment dans le but de contribuer, à terme, à l’élaboration de règles de calcul simples de la portance des fondations profondes énergétiques. Tout d’abord, une synthèse des phénomènes physiques régissant l’interaction thermo-hydro-mécaniques mis en jeu est présentée. Ensuite, considérant le rapport entre le diamètre d’un pieu et sa longueur suffisamment faible, les travaux réalisés se focalisent essentiellement sur les problématiques liées à l’allongement et au raccourcissement du pieu dans sa direction axiale. Différentes modélisation numériques sont effectuées par la méthode des différences finies pour étudier la réponse de pieux énergétiques dans des terrains sans cohésion en tenant compte de différentes conditions aux limites. Le premier modèle est relatif à un pieu énergétique isolé soumis à une seule charge thermique. Le second traite d’un pieu énergétique isolé soumis à une charge axiale mécanique et des variations de température. Le troisième porte sur le comportement des pieux énergétiques appartenant à un groupe de pieux. L’analyse porte en particulier sur l'interaction entre ces pieux et les autres pieux classiques. Dans tous les cas, afin de rendre compte correctement des effets cycliques, l’interface sol-pieu est modélisée par la loi ‘Modjoin’ développée au LGCgE. Enfin, un modèle unidimensionnel basé sur la méthode de courbes de transfert de type t–z est mis en oeuvre. Une loi t–z prenant en compte les effets de chargements cycliques est mise au point. Elle permet notamment de gérer la non-linéarité des phénomènes cycliques et de rendre compte de différents types d’écrouissage.The recent technology for the heating/cooling building system, known as thermo-active piles, has effectively reduced the land use area and drilling cost by incorporating the vertical closed-loop heat exchanger pipes into the pile foundations. The heat transfer principle remains the same with the conventional ground heat exchanger system: an extraction of the steady ground temperature during winter and a recharge of the ground thermal energy during summer. Indeed, the energy transfer in the thermo-active pile system is becoming more complex owing to the thermo-hydro-mechanical interaction between the ground, the aquifer, the concrete pile, and the overlying building. Recently in France, the implementation of this novelty faces some difficulties due to the lack of understanding about the potential impact of seasonal temperature cycles on the environmental sustainability and the structural safety. Considering those concerns, this thesis conducts the study of the thermo-active piles behavior and their interaction with the structure and the environment in the intention to optimize the geotechnical design of such piles according to the French design standard for the deep foundations. First of all, a study of the physical phenomena occurring in the entire system under the thermo-hydro-mechanical interactions is conducted. Since the ratio of the pile diameter and the pile length is very small, the temperature variations in the pile affect mainly the pile axial response. Thus, the study interest is narrowed to the impact of temperature cycles on the pile bearing capacity by paying a particular attention on modeling the soil–structure interaction with finite difference method. A set of three-dimensional numerical models is performed to understand the thermo-active piles response located in cohesionless soil with consideration of several loading stages and various restraint conditions. The first model concerns a single thermo-active pile subjected to a single thermal load, the second deals with a single thermo-active pile under combined axial mechanical and cyclic thermal loads, and the third one is related to the thermo-active piles located in a group of piles to observe the influence on the other classical bearing piles. The need to properly render the cyclic plasticity behavior in such piles is provided by modeling the interface elements at the soil–pile contact zone using the laboratory-developed law named ‘Modjoin’ law. Otherwise, the load transfer t–z method in one-dimensional model can be an alternative solution in the practical geotechnical design, but no t–z law that takes into account the cyclic fatigue effects exists yet. This study carries out a development of the existing t–z law by integrating the nonlinearity condition and cyclic hardening rules

Étude numérique du comportement des pieux énergétiques dans les sols granulaires

Les pieux énergétiques constituent une technique récente permettant d une part le chauffage et la climatisation de bâtiments et assurant d autre part le rôle de fondations profondes. Cette technique consiste à mettre en place dans des fondations profondes classiques un système échangeur de chaleur. Le principe de transfert de chaleur est similaire à celui utilisé pour des systèmes échangeurs de chaleur conventionnels : un fluide caloporteur permet d extraire de l énergie thermique du sol durant l'hiver et d en injecter durant l été. Dans le cas de pieux énergétiques, l interaction entre le sol, le pieu et la structure ne fait pas seulement appel à des considérations mécaniques mais exigent de tenir compte d aspects thermiques et hydrauliques, ce qui rend relativement complexe la compréhension globale du comportement d un pieu énergétique. Actuellement, en France, la réalisation effective de pieux énergétiques rencontre un certain nombre de difficultés qui sont en partie liées à une connaissance insuffisante des effets des cycles de température sur la pérennité d un système de fondations constitué de pieux échangeurs de chaleur. L objectif de ce mémoire est d apporter quelques éclairages sur ce sujet, notamment dans le but de contribuer, à terme, à l élaboration de règles de calcul simples de la portance des fondations profondes énergétiques. Tout d abord, une synthèse des phénomènes physiques régissant l interaction thermo-hydro-mécaniques mis en jeu est présentée. Ensuite, considérant le rapport entre le diamètre d un pieu et sa longueur suffisamment faible, les travaux réalisés se focalisent essentiellement sur les problématiques liées à l allongement et au raccourcissement du pieu dans sa direction axiale. Différentes modélisation numériques sont effectuées par la méthode des différences finies pour étudier la réponse de pieux énergétiques dans des terrains sans cohésion en tenant compte de différentes conditions aux limites. Le premier modèle est relatif à un pieu énergétique isolé soumis à une seule charge thermique. Le second traite d un pieu énergétique isolé soumis à une charge axiale mécanique et des variations de température. Le troisième porte sur le comportement des pieux énergétiques appartenant à un groupe de pieux. L analyse porte en particulier sur l'interaction entre ces pieux et les autres pieux classiques. Dans tous les cas, afin de rendre compte correctement des effets cycliques, l interface sol-pieu est modélisée par la loi Modjoin développée au LGCgE. Enfin, un modèle unidimensionnel basé sur la méthode de courbes de transfert de type t z est mis en oeuvre. Une loi t z prenant en compte les effets de chargements cycliques est mise au point. Elle permet notamment de gérer la non-linéarité des phénomènes cycliques et de rendre compte de différents types d écrouissage.The recent technology for the heating/cooling building system, known as thermo-active piles, has effectively reduced the land use area and drilling cost by incorporating the vertical closed-loop heat exchanger pipes into the pile foundations. The heat transfer principle remains the same with the conventional ground heat exchanger system: an extraction of the steady ground temperature during winter and a recharge of the ground thermal energy during summer. Indeed, the energy transfer in the thermo-active pile system is becoming more complex owing to the thermo-hydro-mechanical interaction between the ground, the aquifer, the concrete pile, and the overlying building. Recently in France, the implementation of this novelty faces some difficulties due to the lack of understanding about the potential impact of seasonal temperature cycles on the environmental sustainability and the structural safety. Considering those concerns, this thesis conducts the study of the thermo-active piles behavior and their interaction with the structure and the environment in the intention to optimize the geotechnical design of such piles according to the French design standard for the deep foundations. First of all, a study of the physical phenomena occurring in the entire system under the thermo-hydro-mechanical interactions is conducted. Since the ratio of the pile diameter and the pile length is very small, the temperature variations in the pile affect mainly the pile axial response. Thus, the study interest is narrowed to the impact of temperature cycles on the pile bearing capacity by paying a particular attention on modeling the soil structure interaction with finite difference method. A set of three-dimensional numerical models is performed to understand the thermo-active piles response located in cohesionless soil with consideration of several loading stages and various restraint conditions. The first model concerns a single thermo-active pile subjected to a single thermal load, the second deals with a single thermo-active pile under combined axial mechanical and cyclic thermal loads, and the third one is related to the thermo-active piles located in a group of piles to observe the influence on the other classical bearing piles. The need to properly render the cyclic plasticity behavior in such piles is provided by modeling the interface elements at the soil pile contact zone using the laboratory-developed law named Modjoin law. Otherwise, the load transfer t z method in one-dimensional model can be an alternative solution in the practical geotechnical design, but no t z law that takes into account the cyclic fatigue effects exists yet. This study carries out a development of the existing t z law by integrating the nonlinearity condition and cyclic hardening rules.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Numerical analysis of energy piles under different boundary conditions and thermal loading cycles

The thermo- mechanical behavior of energy piles has been studied extensively in recent years. In the present study, a numerical model was adapted to study the effect of various parameters (e.g. heating/cooling temperature, head loading condition and soil stiffness) on the thermo-mechanical behavior of an energy pile installed in unsaturated sandstone. The results from the simulations were compared with measurements from a thermal response test on a prototype energy pile installed beneath a 1-story building at the US Air Force Academy (USAFA) in Colorado Springs, CO. A good agreement was achieved between the results obtained from the prototype and the numerical models. A parametric evaluation were also carried out which indicated the significance of the stiffness of the unsaturated sandstone and pile’s head loading condition on stress-strain response of the energy pile during heating/cooling cycles