A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

Follin, Sven; Hartley, Lee; Rhén, Ingvar; Jackson, P. D.; Joyce, Steven; Roberts, David; Swift, B. T.

doi:10.1007/s10040-013-1080-2

Cited by 112 publications

(88 citation statements)

References 19 publications

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“…When pre-existing fractures are preferentially oriented to the far-field stresses associated with a high stress ratio, considerable shearing would occur and further trigger the rotation of matrix blocks, with some very large openings created (along block boundaries) and strongly heterogeneous fluid flows induced. The simulation results show consistency with previous field observations: only a small portion of fractures are highly conductive (Tsang and Neretnieks 1998;Follin et al 2014); critically stressed faults tend to have much higher hydraulic conductivity (Barton et al 1995;Zoback 2007). The observation that the shear dilation of preexisting fractures has dominant effects on flow localisation based on our simulations is also consistent with the results of previous numerical studies (Min et al 2004;Baghbanan and Jing 2008;Zhao et al 2011).…”

Section: Discussionsupporting

confidence: 91%

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

et al. 2017

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A study about the influence of polyaxial (true-triaxial) stresses on the permeability of a three-dimensional (3D) fractured rock layer is presented. The 3D fracture system is constructed by extruding a two-dimensional (2D) outcrop pattern of a limestone bed that exhibits a ladder structure consisting of a Bthrough-going^joint set abutted by later-stage short fractures. Geomechanical behaviour of the 3D fractured rock in response to in-situ stresses is modelled by the finite-discrete element method, which can capture the deformation of matrix blocks, variation of stress fields, reactivation of pre-existing rough fractures and propagation of new cracks. A series of numerical simulations is designed to load the fractured rock using various polyaxial in-situ stresses and the stress-dependent flow properties are further calculated. The fractured layer tends to exhibit stronger flow localisation and higher equivalent permeability as the far-field stress ratio is increased and the stress field is rotated such that fractures are preferentially oriented for shearing. The shear dilation of pre-existing fractures has dominant effects on flow localisation in the system, while the propagation of new fractures has minor impacts. The role of the overburden stress suggests that the conventional 2D analysis that neglects the effect of the out-of-plane stress (perpendicular to the bedding interface) may provide indicative approximations but not fully capture the polyaxial stress-dependent fracture network behaviour. The results of this study have important implications for understanding the heterogeneous flow of geological fluids (e.g. groundwater, petroleum) in subsurface and upscaling permeability for largescale assessments.

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Section: Discussionsupporting

confidence: 91%

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

et al. 2017

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“…[1][2][3] For example, in the safety assessment of the high-level nuclear waste disposal facilities in crystalline rocks, the nuclide transport is mainly dominated by the groundwater flow in rock fractures. 4 Natural fractures are observed to have a three-dimensional (3D) distribution of local apertures formed by two rough walls that are partially contacted. [5][6][7][8][9] Amongst the various parameters affecting the flow through a fracture, the fracture morphology is a critical factor that can change fracture permeability significantly.…”

Section: Introductionmentioning

confidence: 99%

A Predictive Model of Permeability for Fractal-Based Rough Rock Fractures During Shear

et al. 2017

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This study investigates the roles of fracture roughness, normal stress and shear displacement on the fluid flow characteristics through three-dimensional (3D) self-affine fractal rock fractures, Corresponding author. whose surfaces are generated using the modified successive random additions (SRA) algorithm. A series of numerical shear-flow tests under different normal stresses were conducted on rough rock fractures to calculate the evolutions of fracture aperture and permeability. The results show that the rough surfaces of fractal-based fractures can be described using the scaling parameter Hurst exponent (H), in which H = 3 − D f , where D f is the fractal dimension of 3D single fractures. The joint roughness coefficient (JRC) distribution of fracture profiles follows a Gauss function with a negative linear relationship between H and average JRC. The frequency curves of aperture distributions change from sharp to flat with increasing shear displacement, indicating a more anisotropic and heterogeneous flow pattern. Both the mean aperture and permeability of fracture increase with the increment of surface roughness and decrement of normal stress. At the beginning of shear, the permeability increases remarkably and then gradually becomes steady. A predictive model of permeability using the mean mechanical aperture is proposed and the validity is verified by comparisons with the experimental results reported in literature. The proposed model provides a simple method to approximate permeability of fractal-based rough rock fractures during shear using fracture aperture distribution that can be easily obtained from digitized fracture surface information. 1750051-1

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“…Aiming at solving these problems, the time-domain random-walk (TDRW) method was firstly implemented into the discrete element method (DEM) in this study. During each time step of hydromechanical calculation, hydraulic aperture of each fracture and fluid pressure on fracture surface were calculated according to (15) and (14) to consider the coupled hydromechanical effect. To present the effect of matrix diffusion on nuclide transport, (24) and (27) were adopted to get the breakthrough curves.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, water flow process in fractured rock masses should be studied firstly and foremost. Till now, five models have been found in literatures to simulate the water flow in fractured rock masses, that is, continuous model [3][4][5], dual-continuum model [6][7][8], equivalent continuum model [9][10][11], discrete fracture network (DFN) [12][13][14], and hybrid model [15][16][17]. In continuous model, rock masses are treated as continuum porous media with porosity and permeability and continuum-mechanics formulations can be used to describe flow and transport in media.…”

Section: Literature Review About Nuclide Transport Simulationmentioning

confidence: 99%

Implementation of a Time-Domain Random-Walk Method into a Discrete Element Method to Simulate Nuclide Transport in Fractured Rock Masses

Liu

Chan

et al. 2017

Geofluids

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It is essential to study nuclide transport with underground water in fractured rock masses in order to evaluate potential radionuclide leakage in nuclear waste disposal. A time-domain random-walk (TDRW) method was firstly implemented into a discrete element method (DEM), that is, UDEC, in this paper to address the pressing challenges of modelling the nuclide transport in fractured rock masses such as massive fractures and coupled hydromechanical effect. The implementation was then validated against analytical solutions for nuclide transport in a single fracture and a simple fracture network. After that, the proposed implementation was applied to model the nuclide transport in a complex fracture network investigated in the DECOVALEX 2011 project to analyze the effect of matrix diffusion and stress on the nuclide transport in the fractured rock masses. It was concluded that the implementation of the TDRW method into UDEC provided a valuable tool to study the nuclide transport in the fractured rock masses. Moreover, it was found that the total travel time of the nuclide particles in the fractured rock masses with the matrix diffusion and external stress modelled was much longer than that without the matrix diffusion and external stress modelled.

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A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

Cited by 112 publications

References 19 publications

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

A Predictive Model of Permeability for Fractal-Based Rough Rock Fractures During Shear

Implementation of a Time-Domain Random-Walk Method into a Discrete Element Method to Simulate Nuclide Transport in Fractured Rock Masses

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