Tin Chan

A three-dimensional numerical model for thermohydromechanical deformation with hysteresis in a fractured rock mass ☆

Abstract A three-dimensional finite-element solution to the problem of coupled thermohydromechanical deformation, groundwater flow, and heat transport in deformable fractured porous media is presented in this paper. The governing equations are based on Biot’s consolidation theory for poroelastic materials, extended to the non-isothermal environment. The normal and lateral deformations in joints are simulated by a new joint element. The new joint element is based on the Bandis–Barton models and is capable of simulating normal and lateral deformations with dilatancy, contractancy, and hysteresis due to irrecoverable damages/rubblization. A three-dimensional finite-element code Model Of Transport In Fractured porous media (MOTIF) has been developed based on the theoretical framework presented herein. Verification results with experimental data and analytical solutions are presented in this paper. An application example with flow of fluid through a non-isothermally deforming joint is also presented. Results indicate that non-isothermal deformation could play a major role in the transport of fluid and water-borne substances in fractured rocks.

Thermo-Hydro-Mechanical (T-H-M) Impacts of Glaciation and Implications for Deep Geologic Disposal of Nuclear Waste

Abstract The thermo-hydro-mechanical impacts of extreme climate change on the lithosphere down to depths at which deep repositories might be sited have been simulated. The effects of glaciation, including ice sheet and permafrost development, have been studied using site-specific data by combining four models. A climate model provides the forcing function, and ice sheet, permafrost, and coupled hydromechanical models are used to assess impacts. It is concluded that glaciation occurs on a timescale and has impacts on a depth scale that require it to be analysed in a safety analysis for deep lithosphere disposal of long-lived radionuclides in areas that have been prone to glaciation in the past. The simulations have provided valuable insight about processes and mechanisms likely to influence the long-term performance of a repository, the geosphere, or both. The key impacts are discussed, and appropriate methods identified.

A Finite-Element Study of Potential Coupled Hydromechanical Effects of Glaciation on a Crystalline Rock Mass

Abstract A number of studies related to past and on-going deep repository performance assessments have identified glaciation/deglaciation as major future events in the next few hundred thousand years capable of causing significant impact on the long term performance of the repository system. Bench Mark Test 3 (BMT3) of the international DECOVALEX III project has been designed to study the coupled hydro-mechanical (H-M) impacts of glaciation and deglaciation on the long-term (up to 100 000 years), post-closure performance of the geosphere in which a hypothetical repository is located. The BMT3 is a generic exercise based on simplified geological, hydrogeological and rock mechanical characteristics of a crystalline rock research area in the Canadian Shield. This paper presents the site-scale coupled hydro-mechanical finite-element modelling studies conducted by the AECL and CTH teams. Interim results suggest that coupled hydro-mechanical effects, transient effects and fracture zone structural geometry are important.

Upscaling the Thermohydromechanical Properties of a Fractured Rock Mass Using a Modified Crack Tensor Theory

Abstract A methodology based on the modified crack tensor theory of Oda (1986) was developed for the purposes of upscaling the thermohydromechanical properties for fractured rock mass. The methodology was applied to the Bench Mark Test Case 2 (BMT2) of DECOVALEX III, which is based on a hypothetical site with three fractured rock formations. It was found that the upscaled equivalent rock mass permeability, hydraulic and mechanical porosities, and Youngs modulus approached respective asymptotic values at an upscale length of less than 10 meters. The equivalent properties are highly dependent on effective stress. The theoretically determined values of Youngs modulus and permeability are generally very similar to, or on the same order of magnitude as, those obtained by Nirex and cited in the BMT2 Problem Definition and Description document.

STOCHASTIC FLOW AND TRANSPORT SIMULATIONS OF A THREE-DIMENSIONAL TRACER TEST IN MODERATELY FRACTURED PLUTONIC ROCK

Properties of fractured crystalline rock, especially hydraulic permeability and porosity, can be highly variable spatially. Since it is not possible to completely characterize the subsurface rock properties in every detail, it is customary in performance assessment or safety assessment of geological disposal of used nuclear fuel wastes to resort to stochastic methods to simulate the spatial variability.

Verification and Validation of a Three-Dimensional Finite-Element Code For Coupled Thermo-Hydro-Mechanical and Salinity (T-H-M-C) Modelling in Fractured Rock Masses

Abstract MOTIF is a three-dimensional finite-element code developed to simulate groundwater flow, heat transfer and solute transport in deformable fractured porous media. The code has been subjected to an extensive verification and updating programme since the onset of its development. In this paper, additional verification and validation works with an emphasis on thermo-hydro-mechanical processes are presented. The verification results are based on cases designed to verify thermo-hydro-mechanical coupling terms, and isothermal and non-isothermal consolidations. A number of validation case studies have been conducted on the code. Example results are reported in this paper