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  • 51.
    Jing, Lanru
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Stephansson, Ove
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Special Issue: Research results from the DECOVALEX III & BENCHPAR projects - Preface2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 591-592Article in journal (Other academic)
  • 52. Koyama, T.
    et al.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Particle mechanics approach for simulating micro-structure damage and failure processes of rock core samples due to different fluid salinity2006In: Proc. of the 2nd International Conference on Coupled T-H-M-C Processes in Geo-Systems: Fundamentals, Modeling, Experiments and Applications, GeoProc 2006, 2006, p. 569-574Conference paper (Refereed)
  • 53. Koyama, T.
    et al.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    A numerical study on differences in using Navier-Stokes and Reynolds equations for modeling the fluid flow and particle transport in single rock fractures with shear2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 7, p. 1082-1101Article in journal (Refereed)
    Abstract [en]

    The study on fluid flow and transport processes of rock fractures in most practical applications involves two fundamental issues: the validity of Reynolds equation for fluid flow (as most often assumed) and the effects of shear displacements on the magnitudes and anisotropy of the fluid flow velocity field. The reason for such concerns is that the impact of the surface roughness of rock fractures is still an unresolved challenging issue. The later has been systematically investigated with results showing that shear displacement plays a dominant role on evolutions of fluid velocity fields, for both magnitudes and anisotropy, but the former has not received examinations in details due to the numerical complexities involving solution of the Navier-Stokes (NS) equations and the representations of fracture geometry during shear. The objective of this paper aims to solve this problem through a FEM modeling effort. Applying the COMSOL Multiphysics code (FEM) and assuming a 2D problem, we consider the coupled hydromechanical effect of fracture geometry change due to shear on fluid flow (velocity patterns) and particle transport (streamline/velocity dispersion), using measured topographical data of natural rock fracture surfaces. The fluid flow in the vertical 2D cross-sections of single rock fractures was simulated by solving both the Navier-Stokes and the Reynolds equation, and the particle transport was predicted by the streamline particle tracking method with calculated flow velocity fields (vectors) from the flow simulations, obtaining results such as flow velocity profiles, total flow rates, particle travel time, breakthrough curves and the Peclet number, Pe, respectively. The results obtained using NS and Reynolds equations were compared to illustrate the degree of the validity of the Reynolds equation for general applications in practice since the later is mush more computationally efficient for solving large-scale problems. The flow simulation results show that both the total flow rate and the flow velocity fields in a rough rock fracture predicted by the NS equation were quite different from those predicted by the Reynolds equation. The results show that a roughly 5-10% overestimation on the flow rate is produced when the Reynolds equation is used, and the ideal parabolic velocity profiles defined by the local cubic law, when Reynolds equation is used, is no longer valid, especially when the roughness feature of the fracture surfaces changes with shear. These deviations of flow rate and flow velocity profiles across the fracture aperture have a significant impact on the particle transport behavior and the associated properties, such as the travel time and Peclet number. The deviations increase with increasing flow velocity and become more significant when fracture aperture geometry changes with shear.

  • 54.
    Koyama, Tomofumi
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Fardin, Nader
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Shear-induced anisotropy and heterogeneity of fluid flow in a single rock fracture with translational and rotary shear displacements: a numerical study2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 3, p. 426-426Article in journal (Refereed)
    Abstract [en]

    The effects of rotary shear displacements on fluid flow rates and patterns under shear-flow test conditions were numerically investigated in this paper. A pair of digitized surfaces of a concrete fracture replica of size 250 x 250mm was numerically manipulated to simulate the translational and rotary shearing processes of the sample, which provided the evolution of the aperture distributions during shearing and was used to determine the evolution of the fracture transmissivity field. The translational shear test has bidirectional (x and y) hydraulic head boundary conditions and shearing in the x-direction with 1mm shear displacement interval up to 20mm. The rotary shear test has a 0.5° rotation interval up to 90°. The results of flow simulations show that with increasing rotary shear, the flow rate increases but its pattern becomes rapidly isotropic. For bi-directional translational flow, the flow rate increases with shear but significant channelling, anisotropy and heterogeneity developed with shear displacement. The above flow simulations illustrated the more realistic flow patterns under general fracture deformation modes of translation and rotation, and provided insights for the design of more flexible and complementary laboratory coupled stressflow tests.

  • 55.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Fardin, Nader
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Stephansson, Ove
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Numerical simulation of shear-induced flow anisotropy and scale-dependent aperture and transmissivity evolution of rock fracture replicas2006In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 43, no 1, p. 89-106Article in journal (Refereed)
    Abstract [en]

    Fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using FEM modelling, considering evolutions of aperture and transmissivity with shear displacement history. The distributions of fracture aperture during shearing with large shear displacements were obtained by numerically manipulating relative translational movements between two digitalized surfaces of a rock fracture replica, with changing sample sizes. The scale dependence of the fluid behaviour and properties were also investigated using a fractal approach. The results show that the fracture aperture increases anisotropically during shear with a more pronounced increase in the direction perpendicular to the shear displacement, causing significant fluid flow channelling effect, as also observed by other researchers. This finding may have important impacts on the interpretation of the results of coupled hydro-mechanical experiments for measurements of hydraulic properties of rock fractures because the hydraulic properties are usually calculated from flow test results along the shear directions while ignoring the more significant anisotropic flow perpendicular to the shear direction. This finding indicates that the coupled stress-flow tests of rough rock fractures should be conducted in true three-dimensions if possible. Significant change in fracture aperture/ transmissivity in the out-of-plane direction should be properly evaluated if two-dimensional tests are conducted. Results obtained from numerical simulations also show that fluid flow through a single rough fracture changes with increasing sample size and shear displacements, indicating that representative hydro-mechanical properties of the fractures in the field can only be more reliably determined using samples of large enough sizes beyond the stationarity threshold and tested with larger shear displacements.

  • 56.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Effects of model scale and particle size on micro-mechanical properties and failure processes of rocks - A particle mechanics approach2007In: Engineering analysis with boundary elements, ISSN 0955-7997, E-ISSN 1873-197X, Vol. 31, no 5, p. 458-472Article in journal (Refereed)
    Abstract [en]

    A numerical procedure to determine the equivalent micro-mechanical properties of intact rocks is presented using a stochastic representative elementary volume (REV) concept and a particle mechanics approach. More than 200 models were generated in square regions with side lengths varying from 1 to 10 cm, using the Monte Carlo simulation technique. Generated particle models were then used for the calculation of equivalent micro-mechanical properties. Results with a core sample of diorite from Aspo, Sweden, show that the variance of the calculated values of mechanical properties decrease significantly as the side lengths of particle models increase, reaching a REV side length about 5 cm with an acceptable variation of 5%, which is equal to the minimum diameter of rock specimen for uniaxial compressive tests suggested by ISRM. The complete stress-strain curve of the diorite rock sample was predicted under uniaxial compression, as the basis for evaluating the damage and failure processes. The unique contribution of this paper is its study on impacts of sample size and particle size distributions on mechanical behaviour of rocks when particle mechanics approaches are used.

  • 57.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Effects of shearing processes on the fluid flow and particle transport in a single rock fracture2006In: Rock mechanics in underground construction: ISRM International Symposium 2006 / [ed] Leung, CF Y, Zhou, YX, 2006, p. 408-Conference paper (Refereed)
  • 58.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Fluid flow and tracer transport simulations for rock fractures under normal loading and shear displacement2007In: Proceeding of the 11th Int Congr Rock Mech (ISRM 2007), 2007, p. 47-50Conference paper (Refereed)
  • 59. Koyama, Tomofumi
    et al.
    Li, B
    Jiang, Y
    Jing, Lanru
    Coupled shear-flow tests for rock fractures with visualization of the fluid flow and their numerical situations2008In: International Journal of Geotechnical Engineering, ISSN 1938-6362, Vol. 2, no 3, p. 215-227Article in journal (Refereed)
  • 60.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Li, B.
    Jiang, Y.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Numerical modelling of fluid flow tests in a rock fracture with a special algorithm for contact areas2009In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 36, no 1-2, p. 291-303Article in journal (Refereed)
    Abstract [en]

    The fluid flow in rock fractures during shear processes has been all important issue in rock mechanics and is investigated in this paper using finite element method (FEM), considering evolutions of aperture and transmissivity with shear displacement histories under different normal stress and normal stiffness conditions as measured during laboratory coupled shear-flow tests. The distributions of fracture aperture and its evolution during shearing were calculated from the initial aperture, based on the laser-scanned sample surface roughness results, and shear dilations measured in the laboratory tests. Three normal loading conditions were adopted in the tests: simple normal stress and mixed normal stress and normal stiffness to reflect more realistic in situ conditions. A special algorithm for treatment of the contact areas as zero-aperture elements was used to produce more accurate flow field simulations, which is important for continued simulations of particle transport but often not properly treated in literature. The simulation results agree well with the measured hydraulic apertures and flow rate data obtained from the laboratory tests, showing that complex histories of fracture aperture and tortuous flow fields with changing normal loading conditions and increasing shear displacements. With the new algorithm for contact areas, the tortuous flow fields and channeling effects under normal stress/stiffness conditions during shearing were more realistically captured, which is not possible if traditional techniques by assuming very small aperture values for the contact areas were used. These findings have an important impact on the interpretation of the results of coupled hydro-mechanical experiments of rock fractures, and on more realistic simulations of particle transport processes in fractured rocks.

  • 61.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Li, B.
    Jiang, Y.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Numerical simulations for the effects of normal loading on particle transport in rock fractures during shear2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 8, p. 1403-1419Article in journal (Refereed)
    Abstract [en]

    Fluid flow and tracer transport in a single rock fracture during shear is investigated using the finite element method (FEM) and streamline particle tracking, considering evolutions of aperture and transmissivity with shear displacement histories under different normal stresses, based on laboratory tests. The distributions of fracture aperture and its evolution during shear were calculated from the initial aperture fields, based on the laser-scanned surface roughness of feature replicas of rock fracture specimens, and shear dilations measured during the coupled shear-flow tests in laboratory. The coupled shear-flow tests were performed under two levels of constant normal loading (CNL). A special algorithm for treating the contact areas as zero-aperture elements was used to produce more accurate flow field simulations using FEM. The simulation results agreed well with the flow rate data obtained from the laboratory tests, showing complex histories of fracture aperture and tortuous flow channels with changing normal stresses and increasing shear displacements for the flow parallel with the shear direction. A greater increase was observed for flow in the direction perpendicular to the shear direction, due to the significant flow channels created by the shearing process. From the obtained flow velocity fields, particle transport was predicted using a streamline particle tracking method with the flow velocity fields (vectors) taken from the flow simulations, yielding particle travel times, breakthrough curves, and the Peclet number, Pe. The transport behavior in the fracture is also anisotropic, and advective transport is greater in the direction parallel with the shear direction. The effect of normal stress on the particle transport is significant, and dispersion becomes larger with increasing normal stress.

  • 62. Koyama, Tomofumi
    et al.
    Li, Bo
    Jiang, Yu-Jing
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE).
    Development and Validation of the Approach to Prediction of Mass Fraction of Agglomerated Debris2008In: International Journal of Geotechnical Engineering, ISSN 1938-6362, Vol. 2, no 3, p. 215-227Article in journal (Refereed)
  • 63. Koyama, Tomofumi
    et al.
    Vilarrasa, V.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Particle transport in a rough rock fracture during shear : a numerical study2006In: Proc. of the 2nd International Conference on Coupled T-H-M-C Processes in Geo-Systems:: Fundamentals, Modeling, Experiments and Applications, GeoProc 2006, 2006, p. 575-580Conference paper (Other academic)
  • 64.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Vilarrasa, Victor
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Tracer transport in a rough rock fracture during shear: a numerical study2006In: Proc of the 2nd International Conference on Coupled T-H-M-C Processes in Geo-Systems: Fundamentals, 2006, p. 575-580Conference paper (Refereed)
    Abstract [en]

    The effects of translational shear on particle transport under coupled shear-flow testing conditions in a rough rock fracture were numerically investigated in this study. A pair of digitalized surfaces of a rough concrete fracture replica was numerically manipulated to simulate the translational shearing process without considering normal loading and asperity damage. From the evolutions of the aperture filed during shear, the evolutions of the fracture transmissivity field were determined. Undirectional and bi-directional fluid flow situations were considered, using Finite Element Method (FEM). The results show that translational shear makes rough fractures more permeable, producing a significant change in travel time of the particles. Translational shear yields a significant channelling effect in the direction perpendicular to the shear direction. Bi-directional flow patterns show clearly the shortcommings of the conventional laboratory shear-flow tests with unidirectional flow. These simulations provide a first step towards a better understanding of particle transport in rock fractures.

  • 65.
    Lee, Ho Suk
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Jing, Lanru R
    KTH, Superseded Departments, Land and Water Resources Engineering.
    An inverse stress reconstruction algorithm for modelling excavation and thermo-mechanical effects of rock structures2004In: Engineering analysis with boundary elements, ISSN 0955-7997, E-ISSN 1873-197X, Vol. 28, no 7, p. 833-842Article in journal (Refereed)
    Abstract [en]

    When using boundary element methods for problems with domain effects such as initial/residual stresses, body forces and heating, domain integrals are usually involved. Different numerical algorithms have been developed in the past to deal with these domain integrals, such as interior cell mapping, DRM, MRM, etc., which require considerable code development efforts. To take advantage of the boundary element method (BEM) for simulating fracturing processes, but without additional effort for domain integral calculations or transformations, a hybrid approach is suggested in this paper to simulate the excavation and then no-mechanical process of rock structures. Equivalent boundary tractions reflecting the combined effects of the initial and redistributed thermo-mechanical stresses in the domain of interest at multiple excavation and heating steps are produced by an algorithm of inverse stress reconstruction, in a sense of least-square optimization. The algorithm utilizes resultant stress fields at each excavation and heating step, either measured or produced by other numerical methods of domain-types such as finite element method/finite difference method (FEM/FDM), and calculates the equivalent boundary tractions for further fracturing analysis. In this paper, the inverse stress reconstruction algorithm developed for this purpose, using a truncated singular value decomposition (SVD) technique, is presented. Three examples of verification, two closed-form solutions of problems of elasticity with simple geometry and one example from a predictive modeling of a planned in situ heating experiment in a rock pillar at the Aspo Hard Rock Laboratory (HRL), Southern Sweden, are presented.

  • 66. Li, Bo
    et al.
    Jiang, Yujing
    Koyama, Tomofumi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Tanabashi, Yoshihiko
    Experimental study of the hydro-mechanical behavior of rock joints using a parallel-plate model containing contact areas and artificial fractures2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 3, p. 362-375Article in journal (Refereed)
    Abstract [en]

    In recent years, geological disposal of radioactive wastes is considered to be the most promising option, which requires the understanding of the coupled mechanical, hydraulic and thermal properties of the host rock masses and rock fractures. The hydro-mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses. Laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results, chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions, and the sealing techniques when fluid flow during shear is involved. In this study, a new shear-flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed, under constant normal load (CNL) or constant normal stiffness (CNS) constraint. The topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing. A number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-mechanical behaviour. Some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures.

  • 67. Li, Bo
    et al.
    Zhao, Zhihong
    Jiang, Yujing
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Contact mechanism of a rock fracture subjected to normal loading and its impact on fast closure behavior during initial stage of fluid flow experiment2015In: International journal for numerical and analytical methods in geomechanics (Print), ISSN 0363-9061, E-ISSN 1096-9853, Vol. 39, no 13, p. 1431-1449Article in journal (Refereed)
    Abstract [en]

    Fast closure of rock fractures has been commonly observed in the initial stage of fluid flow experiments at environmental temperatures under low or moderate normal stresses. To fully understand the mechanisms that drive this fast closure, the evolution of local stresses acting on contacting asperities on the fracture surfaces prior to fluid flow tests needs to be evaluated. In this study, we modeled numerically the asperity deformation and failure processes during initial normal loading, by adopting both elastic and elastic-plastic deformation models for the asperities on a real rock fracture with measured surface topography data, and estimated their impact on initial conditions for fluid flow test performed under laboratory conditions. Compared with the previous models that simulate the normal contact of a fracture as the approach of two rigid surfaces without deformations, our models of deformable asperities yielded smaller contact areas and higher stresses on contacting asperities at a given normal stress or normal displacement. The results show that the calculated local stresses were concentrated on the contacts of a few major asperities, resulting in crushing of asperity tips. With these higher contact stresses, however, the predicted closure rates by pressure solution are still several orders of magnitude lower than that of the experimental measurements at the initial stage of fluid flow test. This indicates that single pressure solution may not likely to be the principal compaction mechanism for this fast closure, and that the damages on contacting asperities that occur during the initial normal loading stage may play an important role.

  • 68. Liu, Jian-Jun
    et al.
    Feng, Xia-Ting
    Jing, Lanru
    Chinese Academy of Sciences.
    Theoretical and experimental studies on the fluid-solid coupling processes for oil recovery from low permeability fractured reservoirs2004In: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN 0148-9062, E-ISSN 1879-2073, Vol. 41, no 3, p. 496-496Article in journal (Refereed)
  • 69. Millard, A.
    et al.
    Rejeb, A.
    Chijimatsu, M.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    De Jonge, J.
    Kohlmeier, M.
    Nguyen, T. S.
    Rutqvist, J.
    Souley, M.
    Sugita, Y.
    Evaluation of Thm Coupling on the Safety Assessment of a Nuclear Fuel Waste Repository in a Homogeneous Hard Rock2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications, Elsevier, 2004, no C, p. 211-216Chapter in book (Refereed)
    Abstract [en]

    An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground storage design has been made as part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a homogeneous hard rock. A periodic pattern comprises a single vertical borehole, containing a canister surrounded by an over-pack and a bentonite layer, and the backfilled upper portion of the gallery. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The importance of the rock mass intrinsic permeability has been investigated through three values : 10 -17, 10 -18 and 10 -19 m 2. Comparison of the results predicted by fully coupled THM analysis as well as partially coupled TH, TM and HM analysis, in terms of several predefined indicators, enables us to identify the couplings, which play a crucial role with respect to safety issues. The results demonstrate that temperature is hardly affected by the couplings. In contrast the influence of the couplings on the mechanical stresses is considerable.

  • 70. Millard, A.
    et al.
    Rejeb, A.
    Chijimatsu, M.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    De Jonge, J.
    Kohlmeier, M.
    Nguyen, T. S.
    Rutqvist, J.
    Souley, M.
    Sugita, Y.
    Numerical study of the THM effects on the near-field safety of a hypothetical nuclear waste repository - BMT1 of the DECOVALEX III project. Part 2: Effects of THM coupling in continuous and homogeneous rocks2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 731-744Article in journal (Refereed)
    Abstract [en]

    An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground radioactive waste repository has been made as a part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a continuous and homogeneous hard rock. A periodic repository configuration comprises a single vertical borehole, containing a canister surrounded by an over-pack and a bentonite layer, and the backfilled upper portion of the gallery. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The importance of the rock mass's intrinsic permeability has been investigated through scoping calculations with three values: 10(-17), 10(-18) and 10(-19) m(2). Comparison of the results predicted by fully coupled THM analysis as well as partially coupled TH, TM and HM analyses, in terms of several predefined indicators of importance for performance assessment, enables us to identify the effects of the different combinations of couplings, which play a crucial role with respect to safety issues. The results demonstrate that temperature is hardly affected by the couplings. In contrast, the influence of the couplings on the mechanical stresses is considerable.

  • 71. Min, K. B.
    et al.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Rutqvist, J.
    Tsang, C. F.
    Stephansson, Ove
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Representation of fractured rock masses as equivalent continua using a DFN-DEM approach2005In: / [ed] G. Barla and M. Barla, 2005, p. 531-538Conference paper (Refereed)
  • 72. Min, K. -B
    et al.
    Park, B.
    Kim, H.
    Cho, J. -W
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Experimental and numerical anisotropic rock mechanics2017In: Rock Mechanics and Engineering Volume 1: Principles, CRC Press , 2017, p. 109-138Chapter in book (Other academic)
    Abstract [en]

    Although characterization and numerical modeling of anisotropic rock is a longstanding difficulty in rock mechanics, development and advances are being made for anisotropic rock mechanics in spite of the hurdles associated with it. This chapter provides an overview of anisotropic rock mechanics issues and introduces a series of experimental and numerical anisotropic rock mechanics studies conducted in the past 15 years. Experimental investigations are made on elastic, thermal conductivity, seismic and permeability anisotropy of rock based on cores taken from directional coring system. The first part of numerical anisotropic rock mechanics introduces the numerical experiments to determine the compliance tensor of fractured rock mass with Discrete Fracture Network (DFN) modeled as equivalent continuum anisotropic rock. Blocky Discrete element method (DEM) is employed for this numerical experiment using three boundary conditions in two dimensions. The second part deals with representation of transversely isotropic rock using bonded-particle DEM model with smooth joint model as layers. Both deformation and strength behavior modeled by DEM showed a reasonable agreement with analytical solutions, and laboratory observations. Upscaled model applied to anisotropic foundation demonstrate that large scale application anisotropic DEM model is also feasible. 

  • 73.
    Min, Ki Bok
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Stress-dependent mechanical properties and bounds of Poisson's ratio for fractured rock masses investigated by a DFN-DEM technique2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 3, p. 431-432Article in journal (Refereed)
  • 74.
    Min, Ki Bok
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Stephansson, O
    Determining the equivalent permeability tensor for fractured rock masses using a stochastic REV approach: Method and application to the field data from Sellafield, UK2004In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 12, no 5, p. 497-510Article in journal (Refereed)
    Abstract [en]

    A numerical procedure to determine the equivalent permeability tensor of a fractured rock is presented, using a stochastic REV (Representative Elementary Volume) concept that uses multiple realizations of stochastic DFN (Discrete Fracture Network) models. Ten square DFN models are generated using the Monte Carlo simulations of the fracture system based on the data obtained from a site characterization program at Sellafield, Cumbria, UK. Smaller models with varying sizes of from 0.25 mx0.25 m to 10 mx10 m are extracted from the generated DFN models and are used as two-dimensional geometrical models for calculation of equivalent permeability tensor. The DFN models are also rotated in 30degrees intervals to evaluate the tensor characteristics of calculated directional permeability. Results show that the variance of the calculated permeability values decreases significantly as the side lengths of the DFN models increase, which justifies the existence of a REV. The REV side length found in this analysis is about 5 m and 8 m with 20% and 10% acceptable variations, respectively. The calculated directional permeability values at the REV size have tensor characteristic that is confirmed by a close approximation of an ellipse in a polar plot of the reciprocal of square roots of the directional permeability.

  • 75.
    Min, Ki Bok
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Rutqvist, J
    Tsang, C F
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Stress-dependent permeability of fractured rock masses: a numerical study2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 7, p. 1191-1210Article in journal (Refereed)
    Abstract [en]

    We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization. A series of "numerical" experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant. These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough. Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures. Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.

  • 76.
    Min, Ki-Bok
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Stephansson, Ove
    Effect of stress on mechanical and hydraulic rock mass properties: Application of DFN-DEM approach on the data from site investigation at Forsmark, Sweden2005In: EUROCK 2005: IMPACT OF HUMAN ACTIVITY ON THE GEOLOGICAL ENVIRONMENT / [ed] Konecny P, LEIDEN: A A BALKEMA PUBLISHERS , 2005, p. 389-395Conference paper (Refereed)
    Abstract [en]

    The purpose of this study is to demonstrate the effect of virgin rock stresses on the deformability and permeability of fractured rocks. Geological data were taken from the site investigation at Forsmark, Sweden, conducted by SKB. A set of numerical experiments was conducted to determine the equivalent mechanical properties (essentially, elastic moduli and Poisson's ratio) and permeability using the DFN-DEM (Discrete Fracture Network - Distinct Element Method) approach. The results show that both mechanical properties and permeability are highly dependent on stress. Stress-induced anisotropy of mechanical properties was caused by hyperbolic nature of stiffness of the individual fractures. Stress induced anisotropy of permeability was observed due to different closure behavior of fractures, and in situ stresses influence the fluid pathways in the fractured rock mass. This study shows that proper characterization and consideration of in situ stress is important for the understanding of both mechanical and hydraulic behavior of fractured rocks.

  • 77.
    Min, Ki-Bok
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Rutqvist, J.
    Tsang, C. -F
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    A Block-Scale Stress-Permeability Relationship of a Fractured Rock Determined by Numerical Experiments2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications, Elsevier, 2004, no C, p. 269-274Chapter in book (Refereed)
    Abstract [en]

    We present the stress induced permeability change in a fractured rock with special focuses on 1) fracture closure/opening process, 2) anisotropic stress conditions, and 3) fracture dilation. In order to overcome the limitations from the experimental study on a single fracture or analytical study on orthogonal and/or persistent fracture models, realistic Discrete Fracture Network (DFN) models were used as a geometrical basis. A series of numerical experiments on fluid flow are conducted under different stress boundary conditions for calculation of equivalent permeability. From the analysis on the realistic DFN model, this paper demonstrates the decrease of permeability with the fracture normal closure, increased anisotropy in permeability with anisotropic stress and increase of permeability and significant channelling effect due to fracture dilation. It is shown that block-scale permeability change in fractured rock depends not only on stress magnitude but also on stress orientation and differential stresses.

  • 78.
    Min, Ki-Bok
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Rutqvist, J
    Tsang, C F
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Thermally induced mechanical and permeability changes around a nuclear waste repository - a far-field study based on equivalent properties determined by a discrete approach2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 765-780Article in journal (Refereed)
    Abstract [en]

    A numerical investigation is conducted on the impacts of the thermal loading history on the evolution of mechanical response and permeability field of a fractured rock mass containing a hypothetical nuclear waste repository. The geological data are extracted from the site investigation results at Sellafield, England. A combined methodology of discrete and continuum approaches is presented. The results of a series of simulations based on the DFN-DEM (discrete fracture network-distinct element method) approach provide the mechanical and hydraulic properties of fractured rock masses, and their stress-dependencies. These properties are calculated on a representative scale that depends on fracture network characteristics and constitutive models of intact rock and fractures. In the present study, data indicate that the large scale domain can be divided into four regions with different property sets corresponding to the depth. The results derived by the DFN-DEM approach are then passed on to a large-scale analysis of the far-field problem for the equivalent continuum analysis. The large-scale far-field analysis is conducted using a FEM code, ROCMAS for coupled thermo-mechanical process. The results show that the thermal stresses of fractured rock masses vary significantly with mechanical properties determined at the representative scale. Vertical heaving and horizontal tensile displacement are observed above the repository. Observed stress and displacement fields also shows significant dependency on how the mechanical properties are characterized. The permeability changes induced by the thermal loading show that it generally decreases close to the repository. However, change of permeability is small, i.e., a factor of two, and thermally induced dilation of fracture was not observed. Note that the repository excavation effects were not considered in the study. The work presented in this paper is the result of efforts on a benchmark test (BMT2) within the international co-operative projects DECOVALEX III and BENCHPAR.

  • 79. Nguyen, T. S.
    et al.
    Borgesson, L.
    Chijimatsu, M.
    Rutqvist, J.
    Fujita, T.
    Hernelind, J.
    Kobayashi, A.
    Ohnishi, Y.
    Tanaka, M.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Hydro-mechanical response of a fractured granitic rock mass to excavation of a test pit - the Kamaishi Mine experiment in Japan2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 1, p. 79-94Article in journal (Refereed)
    Abstract [en]

    A thermo-hydro-mechanical experiment was conducted in a fractured granitic ruck mass at the Kamaishi Mine in Japan. The experiment consists of the excavation of a cylindrical test pit on the floor of an experimental drift. The test pit was then lilted with bentonite with an embedded heater. During the excavation of the test pit, the hydromechanical response of the surrounding rock was monitored. This paper presents the efforts of four research teams to numerically simulate the hydro-mechanical response of the rock mass during excavation. While the total inflow rate to the test pit, the flow distribution on the pit walls and the displacements in the rock mass away From the pit could be reasonably predicted, the pore pressure in individual boreholes, and the expansion behaviour of the pit were less successfully simulated. The reasons for these discrepancies are discussed in the paper.

  • 80. Nguyen, T. S.
    et al.
    Chijimatsu, M.
    De Jonge, J.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Kohlmeier, M.
    Millard, A.
    Rejeb, A.
    Rutqvist, J.
    Souley, M.
    Sugita, Y.
    Implications of Coupled Thermo-Hydro-Mechanical Processes on the Safety of a Hypothetical Nuclear Fuel Waste Repository2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications, Elsevier, 2004, no C, p. 225-230Chapter in book (Refereed)
    Abstract [en]

    In Bench Mark Test no. 1 (BMT1) of the DECOVALEX III international project, we looked at the implications of coupled thermo-hydro-mechanical (THM) processes on the safety of a hypothetical nuclear waste repository. The research teams first calibrated their models with the results of an in-situ heater experiments to obtain confidence in the capability of the models to simulate the main physical processes. Then the models were used to perform scoping calculations for the near-field of the hypothetical repository, with varying degrees of THM coupling complexity. The general conclusion from the BMT1 exercise is that it would be prudent to perform full THM coupling analyses for two main reasons. First, several safety features might be overlooked with lesser degrees of coupling. Second, the ability to predict and interpret several physical processes, during the post-closure monitoring period, is important for confidence building and public acceptance. Such ability is attainable only with fully coupled THM models.

  • 81. Nguyen, Thanh Son
    et al.
    Börgesson, Lennart
    Chijimatsu, Masakazu
    Hernelind, Jan
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Kobayashi, Akira
    Rutqvist, Jonny
    A case study on the influence of THM coupling on the near field safety of a spent fuel repository in sparsely fractured granite2009In: Environmental Geology, ISSN 0943-0105, E-ISSN 1432-0495, Vol. 57, no 6, p. 1239-1254Article in journal (Refereed)
    Abstract [en]

    In order to demonstrate the feasibility of geological disposal of spent CANDU fuel in Canada, a safety assessment was performed for a hypothetical repository in the Canadian Shield. The assessment shows that the maximum long term radionuclide release from such repository would meet international criteria for dose rate; however, uncertainties in the assumed evolution of the repository were identified. Such uncertainties could be resolved by the consideration of coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes. In Task A of the DECOVALEX-THMC project, THM models were developed within the framework of the theory of poroelasticity. Such model development was performed in an iterative manner, using experimental data from laboratory and field tests. The models were used to perform near-field simulations of the evolution of the repository in order to address the above-mentioned uncertainties. This paper presents the definition and rationale of task A and the results of the simulations. From a repository safety point of view, the simulations predict that the maximum temperature would be well below the design target of 100A degrees C; however, the stress on the container can marginally exceed the design value of 15 MPa. However, the most important finding from the simulations is that a rock damage zone could form around the emplacement borehole. Such damage zone can extend a few metres from the walls of the emplacement holes, with permeability values that are orders of magnitude higher than the initial values. The damage zone has the potential to increase the radionuclide transport flux from the geosphere; the effect of such an increase should be taken into account in the safety assessment and mitigated if necessary by the provision of sealing systems.

  • 82.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Anisotropy of strength and deformability of fractured rocks2014In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 6, no 1, p. 156-164Article in journal (Refereed)
    Abstract [en]

    Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue fordesign and stability assessments of rock engineering structures, due mainly to the non-uniform and nonregulargeometries of the fracture systems. However, no adequate efforts have been made to study thisissue due to the current practical impossibility of laboratory tests with samples of large volumes containingmany fractures, and the difficulty for controlling reliable initial and boundary conditions forlarge-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy offractured rock masses is needed. The objective of this study is to systematically investigate anisotropy ofstrength and deformability of fractured rocks, which has not been conducted in the past, using a numericalmodeling method. A series of realistic two-dimensional (2D) discrete fracture network (DFN)models were established based on site investigation data, which were then loaded in different directions,using the code UDEC of discrete element method (DEM), with changing confining pressures. Numericalresults show that strength envelopes and elastic deformability parameters of tested numerical modelsare significantly anisotropic, and vary with changing axial loading and confining pressures. The resultsindicate that for design and safety assessments of rock engineering projects, the directional variations ofstrength and deformability of the fractured rock mass concerned must be treated properly with respectto the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnelsin association with principal stress directions only may not be adequate for safety requirements.Outstanding issues of the present study and suggestions for future study are also presented.

  • 83.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Effects of loading conditions on strength and deformability of fractured rocks - A numerical study2014In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium, Taylor & Francis Group, 2014, p. 365-368Conference paper (Refereed)
    Abstract [en]

    This paper presents a systematic numerical study to evaluate the effects of two different loading conditions, namely the axial stress and axial velocity, on testing compressive strength and deformability properties of fractured rocks. The UDEC code was used to perform a series of numerical tests on two-dimensional fracture network (DFN) models, in the similar ways for the uniaxial and biaxial laboratory testing on intact rock samples. The obtained stresses and strains from these numerical experiments were used to estimate equivalent directional Young's modulus and fit the Mohr-Coulomb and Hoek-Brown failure criteria, represented by equivalent material properties defining these two criteria. The numerical results show that stress-strain behaviors changes by loading conditions with higher averaged axial stress under axial velocity condition than that under axial stress condition. Therefore, the effects of different loading conditions should be carefully considered for designing and interpretation of results for in-situ experiments with large volumes of fractured rocks.

  • 84.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Stochastic analysis of strength and deformability of fracture rocks using multi-fracture system realizationsManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, a systematic numerical framework is presented to predict stochastic variationsof strength and deformation parameters of fracture rocks, using multiple realizations ofstochastic discrete fracture network (DFN) models at established representative elementaryvolume (REV). Fifty 2D square geometrical models, which are generated using the MonteCarlo technique of the fracture system based on the data obtained from a real site, aregenerated for stochastic analysis of results of stress-deformation behaviors from a series of350 compressive numerical experiments, using the discrete element method (DEM). The Chi-Squared goodness-of-fit test was used to frequency and probability and cumulativedistribution functions (PDF-CDF) of the strength and deformability of fracture rocksdistributions. The results show that (i) the Young’s modulus and Poisson’s ratio during elasticdeformation stages have normal and lognormal distributions, respectively, (ii) both thefriction angle and cohesion derived from Mohr-Coulomb (M-C) strength criterion obeynormal distributions, (iii) the m and s parameters of Hoek-Brown (H-B) strength criterionhave lognormal distributions. The results of stochastic analysis show that it is a usefultechnique for evaluating random variations of strength and deformability parameters of thefractured rock, in cases where there is significant scatter in the rock and fracture parameters.

  • 85.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. University of Kashan, Iran.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Stochastic analysis of strength and deformability of fractured rocks using multi-fracture system realizations2015In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 78, p. 108-117Article in journal (Refereed)
  • 86.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Water pressure effects on strength and deformability of fractured rocks under low confining pressures2015In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 48, no 3, p. 971-985Article in journal (Refereed)
    Abstract [en]

    The effect of groundwater on strength anddeformation behavior of fractured crystalline rocks is one ofthe important issues for design, performance and safetyassessments of surface and subsurface rock engineeringproblems. However, practical difficulties make the directin situ and laboratory measurements of these properties offractured rocks impossible at present, since effects of complexfracture system hidden inside the rock masses cannot beaccurately estimated. Therefore, numerical modeling needs tobe applied. The overall objective of this paper is to deepenour understanding on the validity of the effective stressconcept, and to evaluate the effects of water pressure onstrength and deformation parameters. The approach adopteduses discrete element methods to simulate the coupled stressdeformation-flow processes in a fractured rock mass withmodel dimensions at a representative elementary volume(REV) size and realistic representation of fracture systemgeometry. The obtained numerical results demonstrate thatwater pressure has significant influence on the strength, butwith minor effects on elastic deformation parameters, comparedwith significant influence by the lateral confiningpressure. Also, the classical effective stress concept to fracturedrock can be quite different with that applied in soilmechanics. Therefore, one should be cautious when applyingthe classical effective stress concept to fractured rock media.

  • 87.
    Noorian-Bidgoli, Majid
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Zhao, Zhihong
    Stockholm University.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Numerical evaluation of strength and deformability of fractured rocks2013In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 5, no 6, p. 419-430Article in journal (Refereed)
    Abstract [en]

    Knowledge of the strength and deformability of fractured rocks is important for design, construction andstability evaluation of slopes, foundations and underground excavations in civil and mining engineering.However, laboratory tests of intact rock samples cannot provide information about the strength anddeformation behaviors of fractured rock masses that include many fractures of varying sizes, orientationsand locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costlyand often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numericalpredicting using discrete element methods (DEM) is a suitable approach for such modeling because of theiradvantages of explicit representations of both fractures system geometry and their constitutive behaviorsof fractures, besides that of intact rock matrix. In this study, to generically determine the compressivestrength of fractured rock masses, a series of numerical experiments were performed on two-dimensionaldiscrete fracture network models based on the realistic geometrical and mechanical data of fracturesystems from field mapping. We used the UDEC code and a numerical servo-controlled program forcontrolling the progressive compressive loading process to avoid sudden violent failure of the models.The two loading conditions applied are similar to the standard laboratory testing for intact rock samplesin order to check possible differences caused by such loading conditions. Numerical results show thatthe strength of fractured rocks increases with the increasing confining pressure, and that deformationbehavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses andstrains obtained from these numerical experiments were used to fit the well-known Mohr-Coulomb (MC)and Hoek-Brown (H-B) failure criteria, represented by equivalent material properties defining thesetwo criteria. The results show that both criteria can provide fair estimates of the compressive strengthsfor all tested numerical models. Parameters of the elastic deformability of fractured models during elasticdeformation stages were also evaluated, and represented as equivalent Young’s modulus and Poisson’sratio as functions of lateral confining pressure. It is the first time that such systematic numerical predictingfor strength of fractured rocks was performed considering different loading conditions, with importantfindings for different behaviors of fractured rock masses, compared with testing intact rock samples undersimilar loading conditions.

  • 88. Rutqvist, J.
    et al.
    Borgesson, L.
    Chijimatsu, M.
    Kobayashi, A.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Nguyen, T. S.
    Noorishad, J.
    Tsang, C. F.
    Thermohydromechanics of partially saturated geological media: governing equations and formulation of four finite element models2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 1, p. 105-127Article in journal (Refereed)
    Abstract [en]

    This paper presents the general governing equations for coupled thermohydromechanical (THM) processes in saturated and unsaturated geologic formations and reviews four finite element codes fur modeling of such system. Three of the codes are developed for the special purpose of analyzing coupled THM processes in unsaturated porous and fractured geological media, and the fourth is a commercial code that has been used in its standard version, with a few adaptations for this specialized problem. The basic assumptions and fundamental equations for coupled THM processes in unsaturated porous fractured rock are presented. and formulations of the four finite element models are compared.

  • 89. Rutqvist, J.
    et al.
    Borgesson, L.
    Chijimatsu, M.
    Nguyen, T. S.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Noorishad, J.
    Tsang, C. F.
    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 codes2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 1, p. 129-142Article in journal (Refereed)
    Abstract [en]

    Four computer codes were applied for a prediction of coupled thermo-hydro-mechanical responses during an in situ heater experiment which simulates a nuclear waste deposition hole with a waste over-pack and bentonite buffer, surrounded by fractured rock. The elevated temperature in the heater surroundings, which was maintained at 100 C for 8.5 months, generated substantial heat-driven moisture flow and swelling in the clay buffer, and thermal expansion of the surrounding fractured rock. Predicted system responses - including temperature. moisture content, fluid pressure, stress and displacement - were compared to measurements at 70 sensors located both in the clay buffer and the near-field rock. An overall good agreement between modeling and measured results indicates that most thermo-hydro-mechanical responses are fairly well represented by the coupled numerical models. Uncertainties occur for modeling of hydromechanical behavior of the swelling clay buffer at low saturation, modeling of near-field heterogeneous mechanical behavior of the low-stressed fractured reek, and modeling of the rock-buffer interface.

  • 90. Rutqvist, J.
    et al.
    Chijimatsu, M.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Millard, A.
    Nguyen, T. S.
    Rejeb, A.
    Sugita, Y.
    Tsang, C. F.
    A numerical study of 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 rocks2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 745-755Article in journal (Refereed)
    Abstract [en]

    As a part of the international DECOVALEX III project, and the European BENCHPAR project, the impact of thermal-hydrological-mechanical (THM) couplings on the performance of a bentonite-back-filled nuclear waste repository in near-field crystalline rocks is evaluated in a Bench-Mark Test problem (BMT1) and the results are presented in a series of three companion papers in this issue. This is the third paper with focuses on the effects of THM processes at a repository located in a sparsely fractured rock. Several independent coupled THM analyses presented in this paper show that THM couplings have the most significant impact on the mechanical stress evolution, which is important for repository design, construction and post-closure monitoring considerations. The results show that the stress evolution in the bentonite-back-filled excavations and the surrounding rock depends on the post-closure evolution of both fields of temperature and fluid pressure. It is further shown that the time required to full resaturation may play an important role for the mechanical integrity of the repository drifts. In this sense, the presence of hydraulically conducting fractures in the near-field rock might actually improve the mechanical performance of the repository. Hydraulically conducting fractures in the near-field rocks enhances the water supply to the buffers/back-fills, which promotes a more timely process of resaturation and development of swelling pressures in the back-fill, thus provides timely confining stress and support to the rock walls. In one particular case simulated in this study, it was shown that failure in the drift walls could be prevented if the compressive stresses in back-fill were fully developed within 50 yr, which is when thermally induced rock strain begins to create high differential (failure-prone) stresses in the near-field rocks. Published by Elsevier Ltd.

  • 91. Rutqvist, Jonny
    et al.
    Borgesson, Lennart
    Chijimatsu, Masakazu
    Hernelind, Jan
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Kobayashi, Akira
    Nguyen, Son
    Modeling of damage, permeability changes and pressure responses during excavation of the TSX tunnel in granitic rock at URL, Canada2009In: Environmental Geology, ISSN 0943-0105, E-ISSN 1432-0495, Vol. 57, no 6, p. 1263-1274Article in journal (Refereed)
    Abstract [en]

    This paper presents numerical modeling of excavation-induced damage, permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone (EDZ) around the tunnel. Using in situ calibration of model parameters, the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill-and-blast operation. The modeling showed that stress-induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric (shear) stress, whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress. The remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill-and-blast operation. Moreover, a reasonably good agreement was achieved between simulated and observed excavation-induced pressure responses around the TSX tunnel for 1 year following its excavation. The simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress, with corresponding contraction or expansion of the pore volume. The simulation results for pressure evolution were consistent with previous studies, indicating that the observed pressure responses could be captured in a Biot model using a relatively low Biot-Willis' coefficient, alpha a parts per thousand 0.2, a porosity of n a parts per thousand 0.007, and a relatively low permeability of k a parts per thousand 2 x 10(-22) m(2), which is consistent with the very tight, unfractured granite at the site.

  • 92. Rutqvist, Jonny
    et al.
    Bäckström, Ann
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Chijimatsu, Masakazu
    Feng, Xia-Ting
    Pan, Peng-Zhi
    Hudson, John
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Kobayashi, Akira
    Koyama, Tomofumi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Lee, Hee-Suk
    Huang, Xiao-Hua
    Rinne, Mikael
    Shen, Baotang
    A multiple-code simulation study of the long-term EDZ evolution of geological nuclear waste repositories2009In: Environmental Geology, ISSN 0943-0105, E-ISSN 1432-0495, Vol. 57, no 6, p. 1313-1324Article in journal (Refereed)
    Abstract [en]

    This simulation study shows how widely different model approaches can be adapted to model the evolution of the excavation disturbed zone (EDZ) around a heated nuclear waste emplacement drift in fractured rock. The study includes modeling of coupled thermal-hydrological-mechanical (THM) processes, with simplified consideration of chemical coupling in terms of time-dependent strength degradation or subcritical crack growth. The different model approaches applied in this study include boundary element, finite element, finite difference, particle mechanics, and elasto-plastic cellular automata methods. The simulation results indicate that thermally induced differential stresses near the top of the emplacement drift may cause progressive failure and permeability changes during the first 100 years (i.e., after emplacement and drift closure). Moreover, the results indicate that time-dependent mechanical changes may play only a small role during the first 100 years of increasing temperature and thermal stress, whereas such time-dependency is insignificant after peak temperature, because of decreasing thermal stress.

  • 93.
    Rutqvist, Jonny
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Chijimatsu, M.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Millard, A.
    Nguyen, T. S.
    Rejeb, A.
    Sugita, Y.
    Tsang, C. F.
    Evaluation of the Impact of Thermal-Hydrological-Mechanical Couplings in Bentonite and Near-Field Rock Barriers of a Nuclear Waste Repository in Sparsely Fractured Hard Rock2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications, Elsevier, 2004, no C, p. 217-223Chapter in book (Refereed)
    Abstract [en]

    As part of the international DECOVALEX III project and the European BENCHPAR project, this paper evaluates the impact of thermal-hydrological-mechanical (THM) couplings on the performance of a bentonite back-filled nuclear waste repository in sparsely fractured hard rock. The significance of THM coupling on the performance of a hypothetical repository is evaluated by several independent coupled numerical analyses. Moreover, the influence of a discrete fracture intersecting a deposition hole is discussed. The analysis shows that THM couplings have the most impact on the mechanical behaviour of bentonite-rock system, which is important for repository design considerations.

  • 94. Shabanimashcool, M.
    et al.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. Group of Engineering Geology and Geophysics.
    Li, C. C.
    Discontinuous Modelling of Stratum Cave-in in a Longwall Coal Mine in the Arctic Area2014In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529, Vol. 32, no 5, p. 1239-1252Article in journal (Refereed)
    Abstract [en]

    This paper presents a discontinuous numerical approach for studying roof cave-in mechanisms and obtaining the required support capacity of longwall shields in a case study site, the Svea Nord coal mine in Svalbard. The block size in the roof strata and the mechanical parameters of the discontinuities for the numerical model were obtained through back-calculations. The back-calculations were conducted with a statistical method of design of experiment. Numerical simulations revealed that voussoir jointed beams are formed before the first cave-in occurs. The maximum deflection of a roof stratum in the study site prior to the first cave-in is about 70 % of the stratum thickness. The maximum span of the roof strata prior to the first cave-in depends upon the in situ horizontal stress state. The roof beams have a large stable span when they are subjected to high horizontal stress; but horizontal stress would increase the possibility of rock crushing in deflected roof beams. The simulations and field measurements show no periodic weighting on the longwall shields in the study site. Stiff and strong roof beams would result in large first and periodic cave-in distances. As a consequence of having large cave-in distances, the longwall shields must have high load capacity, which can be calculated by the presented numerical approach.

  • 95. Shen, Baotang
    et al.
    Stephansson, Ove
    Rinne, Mikael
    Lee, Hee-Sok
    Jing, Lanru
    FRACOM Ltd.
    Roshoff, K.
    A fracture propagation code and its applications to nuclear waste disposal2004In: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN 0148-9062, E-ISSN 1879-2073, Vol. 41, no 3, p. 448-449Article in journal (Refereed)
    Abstract [en]

    A two-dimensional fracture propagation code, FRACOD, has been developed. It is based on the original work by Shen and Stephansson (1994) and FRACOM Ltd. (2002) and predict the explicit fracturing process such as fracture initiation and fracture propagation in rock masses. This paper describes the theoretical formulations and the recent developments of FRACOD. The code has been recently used to study rock mass stability for nuclear waste disposal problems. Two case studies are presented in this paper. The first case study is to predict the pillar stability for the Äspö Pillar Stability Experiment (APSE, Sweden) which is designed to test the spalling behaviour of a pillar between two deposition holes under excavation and high thermal stresses. The second case study is to analyse the stability and the extents of Excavation Disturbed Zone (EDZ) of a vertical shaft and horizontal gallery at MIU site in Japan. The results of the two case studies are presented and discussed.

  • 96.
    Stephansson, Ove
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Hudson, J.
    Jing, Lanru
    KTH, Superseded Departments, Land and Water Resources Engineering.
    COUPLED Thermo-Hydro_mechanical_Chemical Processes in Geo-Systems Fundamentals: Modelling, Expriments and Applications2004 (ed. 2)Book (Refereed)
  • 97. Stephansson, Ove
    et al.
    Jing, LanruKTH, Superseded Departments, Land and Water Resources Engineering.Hudson, John
    Coupled THMC processes in geosystems: fundamentals, modeling, experiments and applications2004Collection (editor) (Other academic)
  • 98.
    Tong, Fuguo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Bin, Tian
    A Water Retention Curve Model for the Simulation of Coupled Thermo-Hydro-Mechanical Processes in Geological Porous Media2012In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 91, no 2, p. 509-530Article in journal (Refereed)
    Abstract [en]

    This paper presents a new water retention curve (WRC) model for the simulation of coupled thermo-hydro-mechanical processes in geological porous media. The model simultaneously considers the impact of porosity and temperature on suction, for both wetting processes and drying processes. The model is based on an idealization of porous geological media as having an isotropic and homogeneous microscopic pore structure. Suction is expressed as a function of degree of saturation, porosity, surface tension of the water-air interface, and the length of air bubble perimeter of the pores per unit area on a random 2D cross-section of the medium. The tension of water-air interface is written as a function of temperature, and the length of perimeter of the water-air interface of the pores becomes a function of porosity and degree of saturation. The final equation of the new WRC is a function of suction, effective degree of saturation, temperature, porosity, pore-gas pressure, and the rate of degree of saturation change with time for both wetting and drying processes. The model was used to fit experimental data of the FEBEX bentonite, with good agreements between measured and calculated results.

  • 99.
    Tong, Fuguo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Zimmerman, R. W.
    A fully-coupled finite element code for modeling thermo-hydro-mechanical processes in porous geological media2009In: 43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium, American Rock Mechanics Association (ARMA), 2009Conference paper (Refereed)
    Abstract [en]

    This paper describes a new FEM code for modeling coupled thermo-hydro-mechanical processes in porous geological media. For three-dimensional problems, six governing equations, which are based on the conservation equations of momentum, mass, and energy, are presented to describe the coupled THM processes. The three displacement components, the temperature, the pore fluid pressure and the porosity are chosen as the six primary variables. The governing continuum equations are discretized in space by using the Galerkin finite element formulation, and are discretized in time by one-dimensional finite difference scheme. This leads to a large non-symmetric matrix equation that has many small entries along its diagonal, and is therefore ill-conditioned. For efficient equation solution, some special numerical techniques are used in the code in order to deal with the problem of a large non-symmetric ill-conditioned matrix equation. The code was validated against several classical analytical solutions to problems in poroelasticity and thermoelasticity, and tested against a benchmark laboratory experiment that was performed in the Polytechnic University of Catalonia (UPC), Spain.

  • 100.
    Tong, Fuguo
    et al.
    KTH.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Zimmerman, R. W.
    Modeling multiphase flow, deformation and heat transfer in buffer2009In: ISRM International Symposium on Rock Mechanics, SINOROCK 2009, International Society for Rock Mechanics , 2009Conference paper (Refereed)
    Abstract [en]

    This paper presents a new FEM approach and computer code for modeling fully coupled thermo-hydro-mechanical processes associated with underground nuclear waste repositories. The governing equations are based on the theory of mixtures applied to the multiphysics of porous media, considering solid-phase deformation, liquid-phase flow, gas flow, heat transport, thermally-induced water flow, phase change of water, and swelling deformation in buffer materials. For three-dimensional problems, three displacement components, water pressure, gas pressure, vapor pressure and porosity are chosen as the eight primary variables. The code was tested against a benchmark test that was performed in laboratory conditions on vertical cylindrical columns of compacted MX-80 bentonite by the French Commission of Atomic Energy from 2003 to 2004. The comparison with the benchmark tests shows good agreement between the numerical predictions and the measured data, thus providing a partial validation of our new code. Discussion of outstanding issues and conclusions are presented at the end of the paper. © ISRM International Symposium on Rock Mechanics, SINOROCK 2009.

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