Increasing understanding and confidence in THM simulations of engineered barrier systems

Previous studies on the modelling of coupled thermo-hydro-mechanical (THM) processes in bentonite-based engineered barrier systems (EBSs) showed the sensitivity of the output quantities to changes in the input parameters. To investigate the effects of uncertainties on the modelling results, to improve the understanding of the coupled processes active in the repository near field and to gain in-depth understanding of model uncertainties of different codes, a sensitivity analysis and code comparison of EBS simulations was performed within the Task Force on Engineered Barrier Systems. The analysis included variations in material parameter values, boundary and initial conditions, considered physical processes and model geometries, amounting to 60 different cases. This in-depth analysis helped evaluate the influence of parameter and conceptual uncertainties on the results of coupled THM simulations and to identify key parameters and processes. The cross-code comparison encouraged a fruitful exchange among modelling teams and led to very good agreements between the results of the different codes. Serving as a benchmark example for THM-coupled simulations of bentonite-based EBSs, the study helped increase the confidence in the modelling capabilities of several codes used for safety evaluations of repositories for spent fuel and high-level radioactive waste.Peer ReviewedPostprint (author's final draft

A Simple Generation Technique of Complex Geotechnical Computational Model

Given that FLAC3D (a geotechnical calculation software) is difficult to use for building large, complex, and three-dimensional mining models, the current study proposes a fast and a convenient modeling technique that combines the unique advantages of FLAC3D in numerical calculation and those of SURPAC (a mine design software) in three-dimensional modeling, and the interface program was compiled. First, the relationship between the FLAC3D and the SURPAC unit data was examined, and the transformation technique between the data was given. Then, the interface program that transforms the mine design model to calculate the model was compiled using FORTRAN, and the specific steps of the program implementation were described using a large iron and copper mine modeling example. The results show that the proposed transformation technique and its corresponding interface program transformed the SURPAC model into the FLAC3D model, which expedited FLAC3D modeling, verified the validity and feasibility of the transformation technique, and expanded the application spaces of FLAC3D and SURPAC

Advanced Coupled THM Analysis in Geomechanics

This dissertation is aimed at advancing current understating and modeling of problems involving the complex soils systems. A wide range of problems are tackled here including those in: frozen soils; gas hydrate bearing sediments and compressed air energy systems. The soils considered here are affected by changes in temperature fluid pressures and mechanical stresses which would also result in phase change of the constituents in the pore structure. The research conducted here encompasses fundamental; experimental; constitutive and numerical modeling employing the use of coupled formulations. The environmental variables affecting the soil in each case are identified, new or enhanced theoretical formulations and constitutive laws are presented. Particular emphasis is placed on the mechanical constitutive equations, as they are especially important in geotechnical engineering. The formulations presented here are validated against a number of laboratory experiments and case histories that illustrate the relevance and implications of the developments described for geotechnical engineering practice