Use of a Dual-Structure Constitutive Model for Predicting the Long-Term Behavior of an Expansive Clay Buffer in a Nuclear Waste Repository
Publication: International Journal of Geomechanics
Volume 16, Issue 6
Abstract
Expansive soils are suitable as backfill and buffer materials in engineered barrier systems to isolate heat-generating nuclear waste in deep geological formations. The canisters containing nuclear waste would be placed in tunnels excavated at a depth of several hundred meters. The expansive soil should provide enough swelling capacity to support the tunnel walls, thereby reducing the impact of the excavation-damaged zone on the long-term mechanical and flow-barrier performance. In addition to their swelling capacity, expansive soils are characterized by accumulating irreversible strain on suction cycles and by effects of microstructural swelling on water permeability that for backfill or buffer materials can significantly delay the time it takes to reach full saturation. To simulate these characteristics of expansive soils, a dual-structure constitutive model that includes two porosity levels is necessary. The authors present the formulation of a dual-structure model and describe its implementation into a coupled fluid flow and geomechanical numerical simulator. The authors use the Barcelona Basic Model (BBM), which is an elastoplastic constitutive model for unsaturated soils, to model the macrostructure, and it is assumed that the strains of the microstructure, which are volumetric and elastic, induce plastic strain to the macrostructure. The authors tested and demonstrated the capabilities of the implemented dual-structure model by modeling and reproducing observed behavior in two laboratory tests of expansive clay. As observed in the experiments, the simulations yielded nonreversible strain accumulation with suction cycles and a decreasing swelling capacity with increasing confining stress. Finally, the authors modeled, for the first time using a dual-structure model, the long-term (100,000 years) performance of a generic heat-generating nuclear waste repository with waste emplacement in horizontal tunnels backfilled with expansive clay and hosted in a clay rock formation. The thermo-hydro-mechanical results of the dual-structure model were compared with those of the standard single-structure BBM. The main difference between the simulation results from the two models is that the dual-structure model predicted a time to fully saturate the expansive clay barrier on the order of thousands of years, whereas the standard single-structure BBM yielded a time on the order of tens of years. These examples show that a dual-structure model, such as the one presented here, is necessary to properly model the thermo-hydro-mechanical behavior of expansive soils.
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Acknowledgments
Funding for this work was provided by the Used Fuel Disposition Campaign, Office of Nuclear Energy, of the US Department of Energy under Contract Number DE-AC02-05CH11231 with Berkeley Lab. Technical review comments by Dr. Carlos Jove-Colon from Sandia National Laboratories are greatly appreciated.
References
Al-Homoud, A. S., Basma, A. A., Malkawi, A. I. H., and Al-Bashabsheh, M. A. (1995). “Cyclic swelling behavior of clays.” J. Geotech. Eng., 562–565.
Alonso, E. E., Gens, A., and Josa, A. (1990). “A constitutive model for partially saturated soils.” Géotechnique, 40(3), 405–430.
Alonso, E. E., Vaunat, J., and Gens, A. (1999). “Modelling the mechanical behaviour of expansive clays.” Eng. Geol., 54(1–2), 173–183.
Alonso, E. E, et al. (2005). “The FEBEX benchmark test: Case definition and comparison of modeling approaches.” Int. J. Rock Mech. Min. Sci., 42(5–6), 611–638.
Alonso, E. E., and Hoffmann, C. (2007). “Modelling the field behaviour of a granular expansive barrier.” Phys. Chem. Earth., 32(8–14), 850–865.
Åkesson, M., and Kristensson, O. (2008). “Mechanical modeling of MX-80—Development of constitutive laws.” Phys. Chem. Earth., 33, S504–S507.
Blümling, P., Bernier, F., Lebon, P., and Martin, C. D. (2007). “The excavation damaged zone in clay formations time-dependent behaviour and influence on performance assessment.” Phys Chem Earth, 32(8–14), 588–599.
Chen, G. J., and Ledesma, A. (2007). “Coupled solution of heat and moisture flow in unsaturated clay barriers in a repository geometry.” Int. J. Numer. Anal. Methods Geomech., 31(8), 1045–1065.
Corkum, A. G., and Martin, C. D. (2007). “The mechanical behaviour of weak mudstone (Opalinus Clay) at low stresses.” Int. J. Rock Mech. Min. Sci., 44(2), 196–209.
Day, R. W. (1994). “Swell-shrink behavior of compacted clay.” J. Geotech. Eng., 618–623.
Delage, P., Marcial, D., Cui, Y. J., and Ruiz, X. (2006). “Ageing effects in a compacted bentonite: A microstructure approach.” Géotechnique, 56(5), 291–304.
Dixon, D. A., Graham, J., and Gray, M. N. (1999). “Hydraulic conductivity of clays in confined tests under low hydraulic gradients.” Can. Geotech. J., 36(5), 815–825.
Dupray, F., François, B., and Laloui, L. (2013). “Analysis of the FEBEX multi-barrier system including thermoplasticity of unsaturated bentonite.” Int. J. Numer. Anal. Methods Geomech., 37(4), 399–422.
Gens, A., and Alonso, E. (1992). “A framework for the behaviour of unsaturated expansive clays.” Can. Geotech. J., 29(6), 1013–1032.
Gens, A., Sánchez, M., and Sheng, D. (2006). “On constitutive modelling of unsaturated soils.” Acta Geotech., 1(3), 137–147.
Gens, A., Vaunat, J., Garitte, B., and Wileveau, Y. (2007). “In situ behaviour of a stiff layered clay subject to thermal loading, observations and interpretation.” Géotechnique, 57(2), 207–228.
Gens, A., et al. (2009). “A full-scale in situ heating test for high-level nuclear waste disposal: observations, analysis and interpretation.” Géotechnique, 59(4), 377–399.
Gens, A. (2010). “Soil–environmental interactions in geotechnical engineering.” Géotechnique, 60(1), 3–74.
Jurado, A., et al. (2012). “Probabilistic analysis of groundwater-related risks at subsurface excavation sites.” Eng. Geol., 125, 35–44.
Klinkenberg, L. J. (1941). “The permeability of porous media to liquids and gases.” API drilling and production practice, 200–213.
Komine, H., and Ogata, N. (1994). “Experimental study on swelling characteristics of compacted bentonite.” Can. Geotech. J., 31(4), 478–490.
Kristensson, O., and Åkesson, M. (2008). “Mechanical modeling of MX-80–Quick tools for BBM parameter analysis.” Phys. Chem. Earth., 33, S508–S515.
Laloui, L., and Cekerevac, C. (2003). “Thermo-plasticity of clays: An isotropic yield mechanism.” Comput. Geotech., 30(8), 649–660.
Lloret, A., Villar, M. V., Sanchez, M., Gens, A., Pintado, X., and Alonso, E. E. (2003). “Mechanical behaviour of heavily compacted bentonite under high suction changes.” Géotechnique, 53(1), 27–40.
Martinez-Landa, L., and Carrera, J. (2005). “An analysis of hydraulic conductivity scale effects in granite [full-scale engineered barrier experiment (FEBEX), Grimsel, Switzerland].” Water Resour. Res., 41(3), W03006.
Olivella, S., and Gens, A. (2000). “Vapour transport in low permeability unsaturated soils with capillary effects.” Transp. Porous Media, 40(2), 219–241.
Pousada, P.E. (1982). “Deformabilidad de arcillas expansivas bajo succión controlada.” Ph.D. thesis, Technical Univ. Madrid, Madrid, Spain.
Rutqvist, J., et al. (2011). Status of TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations. Comput. Geosci., 37, 739–750.
Rutqvist, J., et al. (2008). “Results from an international simulation study on coupled thermal, hydrological, and mechanical (THM) processes near geological nuclear waste repositories.” Nucl. Technol., 163(1), 101–109.
Rutqvist, J., Ijiri, Y., and Yamamoto, H. (2011). “Implementation of the Barcelona basic model into TOUGH-FLAC for simulations of the geomechanical behavior of unsaturated soils.” Comput. Geosci., 37(6), 751–762.
Rutqvist, J., Zheng, L., Chen, F., Liu, H. H., and Birkholzer, J. (2014). “Modeling of coupled thermo-hydro-mechanical processes with links to geochemistry associated with bentonite-backfilled repository tunnels in clay formations.” Rock Mech. Rock Eng., 47(1), 167–186.
Saiyouri, N., Hicher, P., and Tessier, D. (2000). “Microstructural approach and transfer water modeling in highly compacted unsaturated swelling clays.” Mech. Cohesive-Fract. Mater., 5(1), 41–60.
Sánchez, M., Gens, A., Guimarães, L. N., and Olivella, S. (2005). “A double structure generalized plasticity model for expansive materials.” Int. J. Numer. Anal. Methods Geomech., 29(8), 751–787.
Sánchez, M., Gens, A., Guimarães, L. N., and Olivella, S. (2008). “Implementation algorithm of a generalised plasticity model for swelling clays.” Comput Geotech., 35(6), 860–871.
Sánchez, M., Gens, A., and Olivella, S. (2012). “THM analysis of a large-scale heating test incorporating material fabric changes.” Int. J. Numer. Anal. Methods Geomech., 36(4), 391–421.
Tartakovsky, D. M. (2007). “Probabilistic risk analysis in subsurface hydrology.” Geophys. Res. Lett., 34(5), L05404
Tripathy, S., Subba Rao, K. S., and Fredlund, D. G. (2002). “Water content–void ratio swell-shrink paths of compacted expansive solid.” Can. Geotech. J., 39(4), 938–959.
Tsang, C. F., Bernier, F., and Davies, C. (2005). “Geohydromechanical processes in the excavation damaged zone in crystalline rock, rock salt, and indurated and plastic clays—In the context of radioactive waste disposal.” Int. J. Rock Mech. Min. Sci., 42(1), 109–125.
Vilarrasa, V., Koyama, T., Neretnieks, I., and Jing, L. (2011). “Shear-induced flow channels in a single rock fracture and their effect on solute transport.” Transp. Porous Media, 87(2), 503–523.
Villar, M. V. (1999). “Investigation of the behaviour of bentonite by means of suction-controlled oedometer tests.” Eng. Geol., 54(1), 67–73.
Wang, Q., Cui, Y. J., Tang, A. M., Barnichon, J. D., Saba, S., and Ye, W. M. (2013a). “Hydraulic conductivity and microstructure changes of compacted bentonite/sand mixture during hydration.” Eng. Geol., 164, 67–76.
Wang, Q., Tang, A. M., Cui, Y. J., Barnichon, J. D., and Ye, W. M. (2013b). “Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixtures based on the BExM model.” Comput. Geotech., 54, 49–52.
Yu, L., et al. (2014). “Consequences of the thermal transient on the evolution of the damaged zone around a repository for heat-emitting high-level radioactive waste in a clay formation: a performance assessment perspective.” Rock Mech. Rock Eng., 47(1), 3–19.
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Published In
International Journal of Geomechanics
Volume 16 • Issue 6 • December 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Apr 21, 2014
Accepted: Aug 14, 2015
Published online: Dec 31, 2015
Discussion open until: May 31, 2016
Published in print: Dec 1, 2016
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