TY - JOUR
T1 - A triple porosity hydro-mechanical model for MX-80 bentonite pellet mixtures
AU - Navarro, Vicente
AU - Asensio, Laura
AU - Gharbieh, Heidar
AU - De la Morena, Gema
AU - Pulkkanen, Veli Matti
N1 - Funding Information:
This study was funded in part by Posiva Oy project 2113799, and by FPU Grant FPU15/02655 from the Spanish Ministry of Education awarded to Ms. De la Morena.
Funding Information:
This study was funded in part by Posiva Oy project 2113799, and by FPU Grant FPU15/02655 from the Spanish Ministry of Education awarded to Ms. De la Morena. In addition, we would like to thank Clay Technology and CEA for allowing us to use the results of their experimental work.
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2020/2
Y1 - 2020/2
N2 - This paper describes the application of a triple porosity model to characterise the hydro-mechanical behaviour of MX-80 bentonite pellet mixtures. The macroscopic behaviour of the system was assumed to be fundamentally controlled by three functional levels, the microstructure (associated with the pores existing inside the clay particle aggregates), the Macrostructure 1 (which integrates the space between the aggregates inside the pellets) and the Macrostructure 2 (related to the void space between the pellets). The role played by each functional level in the overall behaviour of the system was modelled by means of an overlapping continua approach. The usual framework in the simulation of the behaviour of compacted bentonite blocks has been adapted to describe the behaviour of the microstructure and the Macrostructure 1. To model the behaviour of the Macrostructure 2, a simplified formulation of granular materials was adopted. To illustrate the capacity of the proposed approach, two hydration tests were simulated in which significantly different pellet mixtures were used: an open mixture with a dry density of 953 kg/m3, and a closed mixture with 1520 kg/m3 of dry density. Despite the difference between the two mixtures, the model allowed very satisfactory fits to be obtained using in both cases the same material parameters. This shows the consistency of the proposed conceptual framework. Since the response of the two Macrostructural levels is differentiated, the model provides a richer description of the mixture behaviour than that obtained using a double porosity model. However, the interest of the model lies not only in its descriptive richness. The differentiation of the effect of both Macrostructural levels improves the description of the time evolution of the system compared with that obtained when using a double porosity model. However, if the Macrostructure 2 is small (as occurs in the second of the two tests analysed), or there is sufficient confinement for the inter-pellet void space to be considerably reduced when the microstructure swells, double porosity models can satisfactorily characterise the performance of the bentonite pellet mixture.
AB - This paper describes the application of a triple porosity model to characterise the hydro-mechanical behaviour of MX-80 bentonite pellet mixtures. The macroscopic behaviour of the system was assumed to be fundamentally controlled by three functional levels, the microstructure (associated with the pores existing inside the clay particle aggregates), the Macrostructure 1 (which integrates the space between the aggregates inside the pellets) and the Macrostructure 2 (related to the void space between the pellets). The role played by each functional level in the overall behaviour of the system was modelled by means of an overlapping continua approach. The usual framework in the simulation of the behaviour of compacted bentonite blocks has been adapted to describe the behaviour of the microstructure and the Macrostructure 1. To model the behaviour of the Macrostructure 2, a simplified formulation of granular materials was adopted. To illustrate the capacity of the proposed approach, two hydration tests were simulated in which significantly different pellet mixtures were used: an open mixture with a dry density of 953 kg/m3, and a closed mixture with 1520 kg/m3 of dry density. Despite the difference between the two mixtures, the model allowed very satisfactory fits to be obtained using in both cases the same material parameters. This shows the consistency of the proposed conceptual framework. Since the response of the two Macrostructural levels is differentiated, the model provides a richer description of the mixture behaviour than that obtained using a double porosity model. However, the interest of the model lies not only in its descriptive richness. The differentiation of the effect of both Macrostructural levels improves the description of the time evolution of the system compared with that obtained when using a double porosity model. However, if the Macrostructure 2 is small (as occurs in the second of the two tests analysed), or there is sufficient confinement for the inter-pellet void space to be considerably reduced when the microstructure swells, double porosity models can satisfactorily characterise the performance of the bentonite pellet mixture.
KW - Bentonite
KW - Bentonite pellet mixtures
KW - Double porosity model
KW - High level radioactive waste
KW - Hydro-mechanical model
KW - Pellets triple porosity model
UR - http://www.scopus.com/inward/record.url?scp=85076885995&partnerID=8YFLogxK
U2 - 10.1016/j.enggeo.2019.105311
DO - 10.1016/j.enggeo.2019.105311
M3 - Article
AN - SCOPUS:85076885995
SN - 0013-7952
VL - 265
JO - Engineering Geology
JF - Engineering Geology
M1 - 105311
ER -