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CEA Saclay, Université Paris Saclay Postdoctoral position (12 months) |
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Earthquake effect on underground facilities |
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Location: CEA | Université Paris-Saclay, France
Keywords: Undergroud structures, Earthquake engineering, Soil liquefaction, Computational structural mechanics, Finite element analysis.
Starting date: anytime
Duration: 12 months
Contat: Dr. Reine Fares (reine.fares@cea.fr), Dr. Vincent Crozet (vincent.crozet@cea.fr) and Dr. Darius Seyedi (darius.seyedi@cea).
Context
The Industrial Centre for Geological Disposal (Cigeo) is a project for a deep geological disposal facility for radioactive waste to be built in France. If authorized, it will serve for disposal of highly radioactive long-lived waste produced by France’s current fleet of nuclear facilities, thereby tackling the associated problems of nuclear waste disposal (https://international.andra.fr/solutions-long-lived-waste/cigeo). The current design is based on a series of horizontal tunnels of different diameters, which will be built within a clay-rich formation (Callovo-Oxfordian Claystone) at around 500 meters depth. Once waste packages are stored in disposal cells, all the access tunnels will be backfilled and locally seal will be put in place to limit water flow and prevent any dissemination of radionuclides outside the repository. The seals are made of a bentonite/sand mixture which has a high swelling capacity and a low water permeability. As a part of the long-term safety demonstration of the repository, it must be demonstrated that the sealing structures can fulfill their functions under seismic loads over their entire lifetime. In order to guarantee this future nuclear waste repository, CEA and Andra are collaborating to work on the potential scientific and engineering challenges involved.
In this context, CEA is in-charge of performing numerical simulations to investigate the possible impact of earthquakes on the sealing structures and their components during the post-closure period. Many studies can be found discussing the seismic response of shallow hollow tunnels (e.g., Asheghabadi and Matinmanesh, 2011; Chakeri et al., 2011; Hleibieh et al., 2014; Tsinidis et al., 2020). However, few studies are available in the literature for deep structures built in soil masses with nonlinear behavior or under undrained conditions (Bobet, 2003). The main goal of the present post-doctoral project is to investigate the impact of the seismic loading on the hydro-mechanical properties (density, porosity and permeability) of underground facilities, which would eventually indulge three-dimensional (3D) non-linear dynamic soil-structure analysis.
Objective and work program
The responses of underground repository to earthquake events are complex due to the spatially and temporally evolving hydro-mechanical properties of the surrounding media and the structure itself. Accurate modeling of the behavior, therefore, requires a coupled multiphysics numerical code with a large library of constitutive models, leading to substantial computational demands. This makes it challenging to efficiently model the seismic responses for these underground repositories within their estimated lifespan of 100 thousand years. The most common and reliable method for evaluating the response of structures to earthquakes is the finite element method. The OpenSees framework was identified for the simulation of geotechnical systems subjected to earthquakes (Mazzoni et al., 2006). The implementation and simulation challenges are identified to be twofold:
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The first challenge will be to model different earthquake scenarios involving a 3D fully nonlinear analysis at different stages in the lifespan of the facility. For that, a number of simulation in 3D for deep facilities needs to be undertaken, considering the saturated soil condition and the nonlinear behavior of materials, a parallel simulation is favorable. Parallelization adds to the challenges here, imposing constrains of careful partitioning of the model and redefining of the boundary conditions on the partitioned FEM model.
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The second challenge will be to process all the obtained data and address material variabilities in a sensitivity analyses. Nowadays, it is possible with parallel computation and access to high performance computing to run and rerun a numerical model with more than a billion of degrees of freedom. In fact, in CEA exceptional resources for numerical computation can be allocated. However, metamodeling process for creating synthetic material variabilities and predicting responses of the underground facility for a time period and for any material property combination, can have a consequent time gain (Nariman et al., 2019; Zhou et al., 2020).
The research will therefore, propose a performance assessment for sequential and parallel finite element numerical modeling for earthquake analysis of deep underground facilities. Then perform a synthetic data sampling to account for material uncertainties and based on the obtained results in the previous assessment, run a sensitivity analysis using a FEM or a metamodeling process. Finally, the results and knowledge gained within the span of this project will be processed and interpreted to provide responses for industrial needs.
Application profile The selected candidate should have a strong background in computational soil mechanics and dynamic behavior of structures. Additional background in signal processing, probabilistic and statistical techniques and knowledge of the OpenSees finite element code would be most appreciated.
Contract Starting date anytime, 12 months duration.
Gross salary According to the CEA salary grid.
Supervision Dr. Reine Fares, Dr. Vincent Crozet and Dr. Darius Seyedi (Seismic Mechanics Studies Lab, CEA Paris Saclay, Paris Saclay University)
Application procedure Please submit electronically (in PDF format): (1) a detailed resume, (2) a motivation letter, (3) at least one reference letter. Applications must be sent within a single compressed folder (named “NAMESurname.zip/rar/…”) to Dr. Reine Fares (reine.fares@cea.fr), Dr. Vincent Crozet (vincent.crozet@cea.fr) and Dr. Darius Seyedi (darius.seyedi@cea).
Host laboratory Mechanical and Thermal Studies Section (SEMT), Seismic
Mechanics Study (EMSI) Lab. CEA Saclay center (Ile de France / Parisian region), France
Partnerships: CEA (Commissariat de l’Energie Atomique et aux Energies Alternatives)
Andra (Agence nationale pour la gestion des déchets radioactifs)
References
Asheghabadi, M.S., Matinmanesh, H., 2011. Finite Element Seismic Analysis of Cylindrical Tunnel in Sandy Soils with Consideration of Soil-Tunnel Interaction. Procedia Engineering, The Proceedings of the Twelfth East Asia-Pacific Conference on Structural Engineering and Construction 14, 3162–3169. https://doi.org/10.1016/j.proeng.2011.07.399
Bobet, A., 2003. Effect of pore water pressure on tunnel support during static and seismic loading. Tunnelling and Underground Space Technology 18, 377–393.
Chakeri, H., Hasanpour, R., Hindistan, M.A., Ünver, B., 2011. Analysis of interaction between tunnels in soft ground by 3D numerical modeling. Bulletin of Engineering Geology and the Environment 70, 439–448.
Hleibieh, J., Wegener, D., Herle, I., 2014. Numerical simulation of a tunnel surrounded by sand under earthquake using a hypoplastic model. Acta Geotech. 9, 631–640. https://doi.org/10.1007/s11440-013-0294-8.
Mazzoni, S., McKenna, F., Scott, M.H., Fenves, G.L., 2006. OpenSees command language manual. Pacific Earthquake Engineering Research (PEER) Center 264, 137–158.
Nariman, N.A., Hussain, R.R., Msekh, M.A., Karampour, P., 2019. Prediction meta-models for the responses of a circular tunnel during earthquakes. Underground Space, Computational Modeling of Fracture in Geotechnical Engineering Part II 4, 31–47. https://doi.org/10.1016/j.undsp.2018.06.003.
Oldeman, L.R., 1992. Global extent of soil degradation, in: Bi-Annual Report 1991-1992/ISRIC. ISRIC, pp. 19–36.
Tsinidis, G., de Silva, F., Anastasopoulos, I., Bilotta, E., Bobet, A., Hashash, Y.M.A., He, C., Kampas, G., Knappett, J., Madabhushi, G., Nikitas, N., Pitilakis, K., Silvestri, F., Viggiani, G., Fuentes, R., 2020. Seismic behaviour of tunnels: From experiments to analysis. Tunnelling and Underground Space Technology 99, 103334. https://doi.org/10.1016/j.tust.2020.103334.
Zhou, M., Shadabfar, M., Huang, H., Leung, Y.F., Uchida, S., 2020. Meta-modelling of coupled thermo-hydro-mechanical behaviour of hydrate reservoir. Computers and Geotechnics 128, 103848.