The application of environmentally friendly technologies that exploit renewable energy sources is key to follow international agreements and directives for the development of carbon neutral buildings and infrastractures. Energy geostructures are an innovative, multifunctionaltechnology that can be used to address the aforementioned challenge. By coupling the role of the ground structures with that of the geothermal heat exchangers, energy geostructures such as so-called energy piles, energy walls and energy tunnels can serve as structural supports as well as heating and cooling elements for buildings and infrastructures.
The analysis and design of energy geostructures requires the integrated knowledge of various, multidisciplinary aspects in the broad field of engineering. The reason for this is because energy geostructures are subjected to the unprecedented combined action of both thermal and mechanical loads, which govern their energy, geotechnical and structural response via multiphysical interaction with the subsurface.
Typical questions that arise in this framework are as follows: What multiphysical phenomena are associated with the geothermal and structural support operations of energy geostructures? How should energy geostructures be analysed and designed from an energy, geotechnical and structural point of view? What will be the behaviour and performance of energy geostructures over time?
The research we perform at the LMS is centred on, without being limited to, the understanding and solution of these questions and problems. The basis of our work consists of observing, measuring, understanding and predicting how energy geostructures behave from a multiphysical perspective. Our goal is to ensure an optimal energy, geotechnical and structural performance of this technology. As a practical application, our work provides answers to actual questions of practitioners and contributes to the dissemination of the energy geostructure technology
Research Group for Energy Geostructures:
Current Research Projects:
Cyclic Thermo-Mechanical Behaviour of Energy Piles
Involved persons: Prof. Dr. Lyesse Laloui, Dr. Melis Sutman, Elena Ravera
Energy piles are an innovative and environmental friendly way of using renewable energy by combining geothermal heat exchange and structural foundation support. As a result of their unique roles, they are exposed to daily and seasonal temperature variations during their lifetime. Temperatures in the pile and in the surrounding soil fluctuate during the day in between operation and stoppage times resulting in short term temperature changes. Furthermore, there is a seasonal increase in temperatures after episodes of heat injection during summer followed by seasonal temperature reductions during heat extraction in winter. These temperature changes may cause axial displacements, additional axial stresses and changes in the shaft resistance with a daily and seasonal cyclic nature along their lengths. Yet, the primary role of energy piles which is the structural support, should not be jeopardized by the effects of these cyclic temperature changes. The main objectives of this work are from a fundamental perspective to understand the long-term behaviour of energy pile groups subjected to cyclic thermo-mechanical load, for which very limited knowledge remains available to date. The response of soils and soil-concrete interfaces to extensive applied thermal cycles still remains a major challenge and may contribute to the development of reliable, long-term predictions of the behaviour and performance of energy pile groups. From a practical perspective, the current interest in the energy geostructure technology requires the development of simplified, yet reliable analysis and design tools.
Figure 1: a) Plan view of the part of the foundation supporting the water retention tank; (b) cross-sections schematically representing the available instrumentation for thermo-mechanical testing; (c) local stratigraphy.
Thermo-Mechanical Performance of Energy Piles Group
Energy piles are one of the innovative and environmental-friendly technologies where piles that are already required for structural support are used for exploiting the near surface geothermal energy for efficient heating and cooling of buildings, with the inclusion of circulation pipes. The dual nature of energy piles eliminates the additional drilling costs compared to traditional boreholes. However, it also leads to unprecedented challenges related to thermally induced effects on pile and soil behaviour, as well as structure-pile-soil interaction. Up to date, the extent of these effects has not been fully understood to this date, which results in uneconomical design of such foundations, preventing their wider use. Currently, there is a lack of rational and practical tools for evaluating the interactions and couplings that occur in a group of energy piles with a slab lying on the soil, which contribute to the response of the foundation.
Analysis and Design of Thermo-Active Diaphragm
Walls from a Holistic Perspective
Thermo-active diaphragm walls, also known as energy walls (EWs), are geotechnical structures typically used for multi-floored basements, shallow train tunnels and underground car parks. Diaphragm walls are composed by reinforced concrete panels and are constructed using a top-down technique. Depending on the depth of the excavation, props or anchors may be needed in order to satisfy the structural and geotechnical safety requirements. The thermal activation of diaphragm walls is made by inserting pipes (usually high density polyethylene (HDPE) pipes) attached to the reinforcing cage. Such civil structures present the top part of the wall exposed to the soil on one side and to the air void on the other side, while the bottom part is embedded in the soil on both sides. Due to the large surface exposed to the soil, these structures show a great potential for geothermal activation. EWs represent a modern and innovative solution to provide heating/cooling to buildings. The thermo-mechanical behaviour of EWs is still poorly understood and represents a hot topic in the development of energy geostructures. A number of challenges have still to be faced by researchers and practitioners either on the thermal behaviour and on the mechanical characterization of such geostructures. During the development of this project various topics will be tackled: from the analysis and optimization of the heat exchangers design to the study of the thermal behaviour, the definition of the roles of geotechnical and structural conditions for the limit state analyses and design. The overall goal of this project is to use an innovative, holistic approach to analyze and design EWs taking into account thermal, geotechnical and structural requirements as well as economic and environmental constraints from a lifecycle perspective. This project is developed in the framework of the Marie-Curie Innovative Training Network project TERRE and accounts for the collaboration between EPFL (Lausanne, Switzerland) and the industrial partner Nobatek (Bordeaux, France).
Sutman, M., Olgun, G. and Laloui, L, Journal of Geotechnical and Geoenvironmental Engineering, DOI: 10.1061/(ASCE)GT.1943-5606.0001992, 2018
Rotta Loria, A.F., Laloui, L, Géotechnique, DOI: 10.1680/jgeot.17.P.213, 2018
Rotta Loria, A.F., Vadrot, A. and Laloui, L,Geomechanics for Energy and the Environment, DOI: 10.1016/j.gete.2018.04.001, 2018
Rotta Loria, A.F., Vadrot, A. and Laloui, L, Computers and Geotechnics. DOI: 10.1016/j.compgeo.2016.12.015, 2017
Rotta Loria, A.F., and Laloui, L, Géotechnique, DOI: 10.1680/jgeot.16.P.139, 2017
Rotta Loria, A.F., and Laloui, L, Géotechnique, DOI: 10.1680/jgeot.16.P.039, 2017
Rotta Loria, A.F., and Laloui, L, Computers and Geotechnics, 2016
Di Donna, A., Rotta Loria, A.F., and Laloui, L., Computers and Geotechnics, 2016
Di Donna, A., Ferrari, A., and Laloui, L., Canadian Geotechnical Journal, 2015
Geoestructuras energéticas: curso intensivo en Lausana. Published in Madrid Subterra on 07 Novemeber 2018
Les géostructures énergétiques: une énergie renouvelable sous nos pieds. Published in TRACES 21 / 2018: Géothermie on 07 November 2018.
Chauffer les bâtiments grâce à leurs fondations en béton. Published in the ‘’24 heures’’ on 10 January 2018.
Stocker la chaleur de l’été en sous-sol. Published in “Terre&Nature” on 21 May 2015.
Thermal Piles under the SwissTech Convention Center. Published in the ”24 heures” on 29 March 2014.
International cooperation Expands Energy Foundation Technology. Published in Deep Foundations on March/April 2013 issue.
Extacting the heat from the ground. Published in La Regione Ticino on 02 February 2012.
Quand les fondations captent la chaleur du sol. Published in Le Moniteur du BTP on 16 December 2011.
Geostrukturen: Mit thermischer Belastung konfrontiert. Published in the Ee-news on 1 July 2011.
The EPFL Congress Center will have energy-efficient foundations. Published in the EPFL news on 25 May 2011.