Use of a Dual-Structure Constitutive Model for Predicting the Long-Term Behavior of an Expansive Clay Buffer in a Nuclear Waste Repository

Investigation of Coupled Processes in Argillite Rock: FY18 Progress

“…The TOUGH-FLAC simulator (Rutqvist et al, 2002;, used within the SFWST Argillite R&D work package, has been adapted for modeling coupled THM processes associated with bentonite backfilled repositories in argillite host rocks. For rigorous modeling of the THM behavior of bentonitebased (swelling) buffer and back-fill materials, the BBM (Barcelona Basic Model) and BExM (Barcelona Expansive Model) have been implemented into TOUGH-FLAC 2014b;Vilarrasa et al, 2016). Constitutive models to describe anisotropic THM behavior of shale rocks have also been adapted.…”

Investigation of Coupled Processes and Impact of High Temperature Limits in Argillite Rock: FY17 Progress. Predecisional Draft

“…This approach enables mechanistic modeling of processes important for long-term buffer stability, including effects of pore-water salinity on swelling (loss of swelling), conversion of smectite to nonexpansive mineral forms (loss of swelling), and swelling pressure versus exchangeable cations. Details of the development, testing and applications of the dual structure model, were presented in the FY2014 milestone report titled "Investigation of Coupled THMC Processes and Reactive Transport: FY14 Progress" (Rutqvist et al 2014a) and have been published in a journal paper (Vilarrasa et al, 2016). The dual structure model is implemented into FLAC3D using the UDM option.…”

“…For nuclear waste isolation, TOUGH-FLAC provides SFWST with a model framework for modeling coupled THM processes in the Engineered Barrier System (EBS) and host rock and their interactions using state-of-the-art macroscopic constitutive models for bentonite, crushed rock salt backfill, clay, salt and crystalline host rocks. For rigorous modeling of the THM behavior of bentonite-based (swelling) buffer and back-fill materials, the BBM (Barcelona Basic Model) and BExM (Barcelona Expansive Model) have been implemented into TOUGH-FLAC (Rutqvist et al, 2011;2014b;Vilarrasa et al, 2016). Modeling of the in situ heater experiments provides a unique opportunity to validate and test the models at realistic, large-scale, in-situ conditions, including the interactions between the host rock and EBS.…”

An overview of TOUGH-based geomechanics models

“…In the recent few years significant advancements of TOUGH-FLAC have been made, extending the simulations to more complex geomechanical processes, especially related to modeling injection-induced fault activation and induced seismicity Rinaldi et al, 2015a), advanced constitutive models for expansive clay in nuclear waste isolation Vilarrasa et al, 2015), and modeling of salt geomechanical processes coupled with temperature and multiphase flow (Blanco-Martín et al, 2015a;2016).…”

“…Related to THM in clay, the implementation of the Barcelona Basic Model for mechanical behavior of unsaturated soils , and the Barcelona Expansive Model (Vilarrasa et al, 2015) for mechanical behavior of expansive soils are important additions for rigorous modeling of bentonite based backfill material. Moreover, the consideration of two structural levels, i.e., macro-and micro-structures in the expansive model, provides a link between mechanics and chemistry for more mechanistic modeling of THMC behavior.…”