Implementation of the Barcelona Basic Model into TOUGH-FLAC for simulations of the geomechanical behavior of unsaturated soils

This paper presents the implementation of the Barcelona Basic Model (BBM) into the TOUGH-FLAC simulator analyzing the geomechanical behavior of unsaturated soils. We implemented the BBM into TOUGH-FLAC by (1) extending an existing FLAC^3^D module for the Modified Cam-Clay (MCC) model in FLAC^3^D and (2) adding computational routines for suction-dependent strain and net stress (i.e., total stress minus gas pressure) for unsaturated soils. We implemented a thermo-elasto-plastic version of the BBM, wherein the soil strength depends on both suction and temperature. The implementation of the BBM into TOUGH-FLAC was verified and tested against several published numerical model simulations and laboratory experiments involving the coupled thermal-hydrological-mechanical (THM) behavior of unsaturated soils. The simulation tests included modeling the mechanical behavior of bentonite-sand mixtures, which are being considered as back-fill and buffer materials for geological disposal of spent nuclear fuel. We also tested and demonstrated the use of the BBM and TOUGH-FLAC for a problem involving the coupled THM processes within a bentonite-backfilled nuclear waste emplacement tunnel. The simulation results indicated complex geomechanical behavior of the bentonite backfill, including a nonuniform distribution of buffer porosity and density that could not be captured in an alternative, simplified, linear-elastic swelling model. As a result of the work presented in this paper, TOUGH-FLAC with BBM is now fully operational and ready to be applied to problems associated with nuclear waste disposal in bentonite-backfilled tunnels, as well as other scientific and engineering problems related to the mechanical behavior of unsaturated soils.

[1]  E. E. Alonsoa,et al.  The FEBEX benchmark test: case definition and comparison of modelling approaches , 2005 .

[2]  Jonny Rutqvist,et al.  Model development and calibration for the coupled thermal, hydraulic and mechanical phenomena of the bentonite , 2009 .

[3]  L. Jing,et al.  Thermohydromechanics of partially saturated geological media : governing equations and formulation of four finite element models , 2001 .

[4]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[5]  Jonny Rutqvist,et al.  Coupled thermo-hydro-mechanical analysis of a heater test in fractured rock and bentonite at Kamaishi Mine : comparison of field results to predictions of four finite element codes , 2001 .

[6]  K. Roscoe,et al.  ON THE GENERALIZED STRESS-STRAIN BEHAVIOUR OF WET CLAY , 1968 .

[7]  Antonio Gens,et al.  A constitutive model for partially saturated soils , 1990 .

[8]  Tom Schanz.  Experimental Unsaturated Soil Mechanics , 2007 .

[9]  Ann Dueck.  Results from Suction Controlled Laboratory Tests on Unsaturated Bentonite – Verification of a Model , 2007 .

[10]  Antonio Gens,et al.  On constitutive modelling of unsaturated soils , 2006 .

[11]  Antonio Gens,et al.  A double structure generalized plasticity model for expansive materials , 2005 .

[12]  Jonny Rutqvist,et al.  Numerical study of the THM effects on the near-field safety of a hypothetical nuclear waste repository - BMT1 of the DECOVALEX III project. Part 3: Effects of THM coupling in sparsely fractured rocks , 2004 .

[13]  Antonio Gens,et al.  Modern issues in non-saturated soils , 1995 .

[14]  Jonny Rutqvist,et al.  Thermo-hydro-mechanical characterisation of a bentonite-based buffer material by laboratory tests and numerical back analyses , 2001 .

[15]  O. Kristensson,et al.  Mechanical modeling of MX-80 – Quick tools for BBM parameter analysis , 2008 .

[16]  Olaf Kolditz,et al.  Results from an International Simulation Study on Coupled Thermal, Hydrological, and Mechanical Processes near Geological Nuclear Waste Repositories , 2008 .

[17]  Jonny Rutqvist,et al.  Status of the TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations , 2011, Comput. Geosci..

[18]  Tomasz Hueckel,et al.  Thermoplasticity of Saturated Soils and Shales: Constitutive Equations , 1990 .

[19]  Olaf Kolditz,et al.  Non-isothermal flow in low permeable porous media: a comparison of Richards’ and two-phase flow approaches , 2010 .

[20]  J. Rutqvist,et al.  A Fully Coupled Three-Dimensional THM Analysis of the Febex in Situ Test with the Rocmas Code: Prediction of THM Behavior in a Bentonite Barrier , 2003 .

[21]  Gudmundur S. Bodvarsson,et al.  A modeling approach for analysis of coupled multiphase fluid flow, heat transfer, and deformation in fractured porous rock , 2002 .

[22]  J. Carrera,et al.  Numerical formulation for a simulator (CODE_BRIGHT) for the coupled analysis of saline media , 1996 .

[23]  Antonio Gens,et al.  A framework for the behaviour of unsaturated expansive clays , 1992 .

[24]  Mattias Åkesson,et al.  Mechanical modeling of MX-80–Development of constitutive laws , 2008 .

[25]  Antonio Gens,et al.  A full-scale in situ heating test for high-level nuclear waste disposal: observations, analysis and interpretation , 2009 .

[26]  Olaf Kolditz,et al.  A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories , 2009 .