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Johan Thörn - One of the best experts on this subject based on the ideXlab platform.
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Swedish grouting design: Hydraulic testing and grout selection
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2016Co-Authors: Åsa Fransson, Johan Funehag, Johan ThörnAbstract:To ensure successful sealing of rock and soil, an adequate description of the system to be grouted is required as a basis for the grouting design and the selection of the grouting material. In rock, the individual fractures and the Hydraulic Apertures of these fractures form the basis of the Swedish grouting design concept. The Hydraulic Aperture is a key parameter when describing grouting behaviour and it is used to determine the extent to which the grout can enter fractures – that is, the penetrability. The Hydraulic Aperture also determines the penetration length, and therefore the grout parameters (e.g. yield stress and viscosity) as well as the grouting pressure and time needed to be adopted to the Hydraulic Aperture. Once these parameters are chosen, a suitable grouting technique can be adopted. Simple, practical rock and grout tests are important inputs to ensure correct design and performance. The aim of this paper is to present a testing procedure and provide examples from laboratory and field ex...
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The Impact of Fracture Geometry on the Hydromechanical Behaviour of Crystalline Rock
2015Co-Authors: Johan ThörnAbstract:Effective construction of tunnels in fractured crystalline rock requires a unified approach for handling rock mechanics and hydrogeological issues. Traditionally, rock mechanics and hydrogeology not only use different nomenclature, they also measure parameters such as e.g. Aperture differently. A description of fractures that includes both fracture surface- and void geometry could be used as a basis for a conceptual model that allows complexity to be added to the descriptions of Hydraulic and mechanical behaviour without contradictions. In this work, hydromechanically coupled experimental setups and methods were developed and used to improve a conceptual model of hydromechanical (HM) fracture behaviour at low compressive stress. Key aspects of the model are Hydraulic Aperture, fracture normal stiffness, the number of contacts between the surfaces, and the aspect ratio, i.e. the relationship between contact point distance and Aperture, thus describing the voids between the surfaces. The experimental setups that were developed comprised equipment for in situ measurements of mechanical deformation due to stepwise Hydraulic injection of fractures close to a tunnel, and a laboratory HM permeameter used in conjunction with fracture topography and Aperture scanning. The latter produced high-resolution Aperture maps of samples at 1.0 MPa, which were related to the flow rates, estimated Hydraulic Aperture and stiffness from the HM permeameter tests of the samples. Aiming at a common Aperture-stiffness relationship for laboratory and in situ tests at different scales, the results were compared to a previously suggested relationship linking Hydraulic Aperture and normal stiffness. A relationship that has been devised from in situ Hydraulic interference tests and is assumed to be valid for low comp-ressional stress across fractures with limited prior deformation. The few laboratory samples tested and the in situ tests performed show agreement with the Aperture-stiffness relationship. A relationship and a conceptual model that have potential to provide support to future studies on hydromechanical behaviour of crystalline rock.
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Hydraulic and Hydromechanical Laboratory Testing of Large Crystalline Rock Cores
Rock Mechanics and Rock Engineering, 2015Co-Authors: Johan Thörn, Lars O. Ericsson, Åsa FranssonAbstract:In this paper, fracture stiffness in rock samples is determined by means of hydromechanical laboratory testing. The aim is three-fold: to develop a procedure for sampling, to update testing equipment and to relate fracture stiffness to the geological history (e.g., stress history and fracture infillings). The Hydraulic properties of twenty rock cores (diameter 190 mm, c. 100 mm high) from the Äspö Hard Rock Laboratory were tested in a permeameter cell under different isotropic pressures up to 2.5 MPa. The flow rate through individual fracture samples was recorded. Four of the samples were re-tested in the permeameter cell using an updated hydromechanical procedure with deformation measurement across the fracture. Four load cycles of gradually increasing cell pressure were applied, resulting in a clearly observed hysteresis effect in the first and second cycles. Hydraulic Aperture changes calculated using the cubic law were compared with their mechanical equivalents. The Aperture changes followed similar trends, although these differed between the samples. Fracture stiffness was determined from the tests, and the stiffness to Hydraulic Aperture relationship was found to follow previously published patterns linked to the storativity of fractures. Differences in stiffness are explained in the context of the geological history of individual samples, particularly their stress history. The paper presents a conceptualisation of the stiffness behaviour, which includes flow properties, geometric properties and the geological stress history of the tested samples.
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Hydromechanical Behaviour of Fractures Close to Tunnels in Crystalline Rock
2013Co-Authors: Johan ThörnAbstract:The deformation and stiffness properties of rock fractures are important measurable parameters when describing their hydromechanical behaviour. Deformation refers to Aperture change. Stiffness refers to the amount of deformation per stress change to which a fracture is subjected. This thesis aims to investigate the stiffness and deformation behaviour of fractures in crystalline rock through in situ and laboratory experiments. The focus in this work is on fracture geometry due to geological stress history. This will result in increased conceptual understanding and accordance between hydromechanical and geomechanical fracture description and behaviour. The in situ measurements consisted of deformation measurements in boreholes and were conducted at the Aspo Hard Rock Laboratory (HRL) and in the Hallandsas Tunnel. The total deformation across the instrumented borehole sections was measured as an effect of Hydraulic pressurisation of the fractures in the nearby rock volume. The results were assessed in terms of deformation and fracture stiffness. The laboratory experiments were conducted as cyclically loaded permeameter measurements of fractured rock core samples from Aspo HRL with simultaneous deformation measurements across the fracture. The tested samples had various geological properties and revealed differences in Hydraulic Aperture and mechanical deformation behaviour across the experimental cycles. The stiffness to Hydraulic Aperture relationship followed a trend identified in the literature and deviations were given plausible explanations related to the geology and geometry of the samples. The results were discussed in the light of the sampled geology and the measurement methods. The measured deformations and corresponding stiffness were found to be reasonable in the light of available knowledge of the local geology and stress situation at the sites.
Åsa Fransson - One of the best experts on this subject based on the ideXlab platform.
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Swedish grouting design: Hydraulic testing and grout selection
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2016Co-Authors: Åsa Fransson, Johan Funehag, Johan ThörnAbstract:To ensure successful sealing of rock and soil, an adequate description of the system to be grouted is required as a basis for the grouting design and the selection of the grouting material. In rock, the individual fractures and the Hydraulic Apertures of these fractures form the basis of the Swedish grouting design concept. The Hydraulic Aperture is a key parameter when describing grouting behaviour and it is used to determine the extent to which the grout can enter fractures – that is, the penetrability. The Hydraulic Aperture also determines the penetration length, and therefore the grout parameters (e.g. yield stress and viscosity) as well as the grouting pressure and time needed to be adopted to the Hydraulic Aperture. Once these parameters are chosen, a suitable grouting technique can be adopted. Simple, practical rock and grout tests are important inputs to ensure correct design and performance. The aim of this paper is to present a testing procedure and provide examples from laboratory and field ex...
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Hydraulic and Hydromechanical Laboratory Testing of Large Crystalline Rock Cores
Rock Mechanics and Rock Engineering, 2015Co-Authors: Johan Thörn, Lars O. Ericsson, Åsa FranssonAbstract:In this paper, fracture stiffness in rock samples is determined by means of hydromechanical laboratory testing. The aim is three-fold: to develop a procedure for sampling, to update testing equipment and to relate fracture stiffness to the geological history (e.g., stress history and fracture infillings). The Hydraulic properties of twenty rock cores (diameter 190 mm, c. 100 mm high) from the Äspö Hard Rock Laboratory were tested in a permeameter cell under different isotropic pressures up to 2.5 MPa. The flow rate through individual fracture samples was recorded. Four of the samples were re-tested in the permeameter cell using an updated hydromechanical procedure with deformation measurement across the fracture. Four load cycles of gradually increasing cell pressure were applied, resulting in a clearly observed hysteresis effect in the first and second cycles. Hydraulic Aperture changes calculated using the cubic law were compared with their mechanical equivalents. The Aperture changes followed similar trends, although these differed between the samples. Fracture stiffness was determined from the tests, and the stiffness to Hydraulic Aperture relationship was found to follow previously published patterns linked to the storativity of fractures. Differences in stiffness are explained in the context of the geological history of individual samples, particularly their stress history. The paper presents a conceptualisation of the stiffness behaviour, which includes flow properties, geometric properties and the geological stress history of the tested samples.
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A swedish grouting design concept: Hydraulic testing and selection of grout
Grouting and Deep Mixing 2012, 2012Co-Authors: Åsa Fransson, Johan Funehag, Magnus Zetterlund, Gunnar Gustafson, Lisa Hernqvist, Christian ButronAbstract:Some grouting boreholes take no grout and some boreholes take too much, two extremes related to grouting technique, grout properties and the properties of fractures intersecting the boreholes. Successful sealing of rock and soil demands an adequate description of the system to be grouted as a basis for grouting design and selection of grouting material. The basis for this Swedish concept of grouting design is the individual fractures and the Hydraulic Apertures, b, of these fractures. The Hydraulic Aperture is an important parameter to describe the grouting behavior and is used to determine if the grout can enter the fractures, the penetrability. The Hydraulic Aperture also determines the penetration length in addition to grout parameters e.g. yield stress, τ0, and viscosity, μg as well as grouting pressure and time. Knowing these parameters, a proper grouting technique can be adapted. Important input for both design and performance are simple and practical tests of rock and grout and the intention of this paper is to present a testing procedure and give examples from laboratory and field experiences that the approach actually works. © 2012 American Society of Civil Engineers.
Chuangbing Zhou - One of the best experts on this subject based on the ideXlab platform.
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Effects of non-darcy flow on heat-flow coupling process in complex fractured rock masses
Journal of Natural Gas Science and Engineering, 2020Co-Authors: Chi Yao, Qinghui Jiang, Yulong Shao, Jianhua Yang, Fan Huang, Chuangbing ZhouAbstract:Abstract This paper presented a heat-flow coupling model for simulation of heat transfer process in complex fractured rock masses considering non-Darcy flow. Firstly, the Forchheimer equation and the Reynolds equation were coupled to obtain the governing equation to describe the non-Darcy flow behaviors. Then, combined with the heat transfer equation and considered the heat exchange process between fractures and rock matrix, the heat-flow coupling model was established. The model was solved by the finite element method. The calculation results of the non-Darcy flow model were compared with the fluid flow test results of crossed fracture and complex fracture network models and a good agreement was observed. The numerical simulation results of non-Darcy flow and heat transfer model were compared with analytical solution of flow-heat coupling in a single fracture, and the numerical solution and the analytical solution agreed well. Finally, a two-dimensional complex fracture network was generated for numerical experiments, and effects of equivalent Hydraulic Aperture df and Hydraulic gradient J on the flow behaviors and the heat-transfer process in complex fractured rock masses were systematically discussed. Results showed that the proposed model can well describe the non-Darcy flow characteristics as well as the heat-flow coupling process in complex fracture networks. Considering the non-Darcy flow behaviors, the average temperature of the outlet dropped slower under non-Darcy than which under Darcy flow. It was also found that effects of non-Darcy flow on the heat transfer process will be more significant as the Hydraulic gradient or the equivalent Hydraulic Aperture increases.
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A Novel Numerical Model for Fluid Flow in 3D Fractured Porous Media Based on an Equivalent Matrix-Fracture Network
Hindawi Limited, 2019Co-Authors: Chi Yao, Qinghui Jiang, Jianhua Yang, Jinsong Huang, Chuangbing ZhouAbstract:An original 3D numerical approach for fluid flow in fractured porous media is proposed. The whole research domain is discretized by the Delaunay tetrahedron based on the concept of node saturation. Tetrahedral blocks are impermeable, and fluid only flows through the interconnected interfaces between blocks. Fractures and the porous matrix are replaced by the triangular interface network, which is the so-called equivalent matrix-fracture network (EMFN). In this way, the three-dimensional seepage problem becomes a two-dimensional problem. The finite element method is used to solve the steady-state flow problem. The big finding is that the ratio of the macroconductivity of the whole interface network to the local conductivity of an interface is linearly related to the cubic root of the number of nodes used for mesh generation. A formula is presented to describe this relationship. With this formula, we can make sure that the EMFN produces the same macroscopic Hydraulic conductivity as the intact rock. The approach is applied in a series of numerical tests to demonstrate its efficiency. Effects of the Hydraulic Aperture of fracture and connectivity of the fracture network on the effective Hydraulic conductivity of fractured rock masses are systematically investigated
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Influence of surface roughness on nonlinear flow behaviors in 3D self-affine rough fractures: Lattice Boltzmann simulations
Advances in Water Resources, 2016Co-Authors: Min Wang, Jia-qing Zhou, Yifeng Chen, Chuangbing ZhouAbstract:This study investigates the impacts of surface roughness on the nonlinear fluid flow through three-dimensional (3D) self-affine rock fractures, whose original surface roughness is decomposed into primary roughness (i.e. the large-scale waviness of the fracture morphology) and secondary roughness (i.e. the small-scale unevenness) with a wavelet analysis technique. A 3D Lattice Boltzmann method (LBM) is adopted to predict the flow physics in rock fractures numerically created with and without consideration of the secondary roughness, respectively. The simulation results show that the primary roughness mostly controls the pressure distribution and fracture flow paths at a large scale, whereas the secondary roughness determines the nonlinear properties of the fluid flow at a local scale. As the pressure gradient increases, the secondary roughness enhances the local complexity of velocity distribution by generating and expanding the eddy flow and back flow regions in the vicinity of asperities. It was found that the Forchheimer's law characterizes well the nonlinear flow behavior in fractures of varying roughness. The inertial effects induced by the primary roughness differ only marginally in fractures with the roughness exponent varying from 0.5 to 0.8, and it is the secondary roughness that significantly enhances the nonlinear flow and leads to earlier onset of nonlinearity. Further examined were the effects of surface roughness on the transmissivity, Hydraulic Aperture and the tortuosity of flow paths, demonstrating again the dominant role of the secondary roughness, especially for the apparent transmissivity and the equivalent Hydraulic Aperture at high pressure gradient or high Reynolds number. The results may enhance our understanding of the role of surface roughness in the nonlinear flow behaviors in natural rock fractures.
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Evaluation of Forchheimer equation coefficients for non-Darcy flow in deformable rough-walled fractures
Journal of Hydrology, 2015Co-Authors: Yifeng Chen, Jia-qing Zhou, Chuangbing ZhouAbstract:Summary This study focuses on experimental evaluation of the Forchheimer equation coefficients for non-Darcy flow in deformable rough-walled fractures. Water flow tests through twelve granite fracture samples with different roughness were conducted in a triaxial cell under confining stresses varying from 1.0 MPa to 30.0 MPa. A total of 2280 experimental data in the form of pressure gradient versus discharge were collected. Three representative types of nonlinear flow behaviors induced by inertial effect, fracture dilation and solid–water interaction, respectively, were observed. Regression analyses of the experimental data show that the Forchheimer equation adequately describes the non-Darcy flow behavior induced by significant inertial effect. Based on the experimental observations, two empirical equations were proposed for parametric expression of the Forchheimer’s nonlinear coefficient, one as a power function of Hydraulic Aperture and the other dependent on both Hydraulic Aperture and peak asperity of the fracture surface. A new criterion was presented for assessing the applicability of Darcy’s law, which relies on the ratio of discharge or pressure gradient predicted by the Forchheimer’s law incorporated with the single-parameter equation to that predicted by the Darcy’s law. A sensitivity analysis was performed using the double-parameter equation for examining the dependence of the Forchheimer’s nonlinear coefficient on peak asperity, demonstrating the importance of incorporating the fracture roughness in the development of non-Darcy flow models. The experimental results and the proposed models are useful for understanding and numerical modeling of the nonlinear flow behaviors in fractured aquifers.
Yudong Zhang - One of the best experts on this subject based on the ideXlab platform.
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Microflow effects on the Hydraulic Aperture of single rough fractures
Advances in Geo-Energy Research, 2019Co-Authors: Ge Zhang, Yudong ZhangAbstract:The understanding of flow behavior in rough fractures is essential for many engineering activities. When the Aperture of a rough fracture approaches the mean free path of fluid molecules, the microflow effect, sometimes also referred to relative rarefaction effect, relative discrete effect or non-equilibrium effect, becomes pronounced. It was found often to enhance the flow rate. However, the surface roughness shows completely contrary influence. In order to clarify the influences of the two factors, a computer simulation work accompanied with theoretical analyses is conducted. Previous empirical models for Hydraulic Aperture which already containing roughness effect are modified with consideration of the microflow effect. Direct simulation using the lattice Boltzmann method is conducted on artificially created 2D fractures with random roughness following Gaussian distribution to reveal the competitive relationship of two effects. The simulation results also verify modified models. Among them, the one based on Rasouli and Hosseinian's model agrees with the simulation on the relationship between Hydraulic Aperture and mechanical Aperture for both cases with very rough fractures and relatively smooth fractures. Further investigation confirms that, under various roughness, the ratio of Hydraulic Aperture over mechanical Aperture shows quantitatively different trends as mechanical Aperture decreases. This phenomenon exists on a relatively wide scale. An equilibrium point of two effects is also found through analysis of the relationship. The results reveal the mechanism of microflow in 2D rough fractures and also provide a reference for engineering problems like the transport of natural gas through microfractures. Cited as : Zhang, G., Zhang, Y., Xu, A., Li, Y. Microflow effects on the Hydraulic Aperture of single rough fractures. Advances in Geo-Energy Research, 2019, 3(1): 104-114, doi: 10.26804/ager.2019.01.09.
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Microflow effects on the Hydraulic Aperture of single rough fractures
Ausasia Science and Technology Press, 2019Co-Authors: Ge Zhang, Yudong ZhangAbstract:The understanding of flow behavior in rough fractures is essential for many engineering activities. When the Aperture of a rough fracture approaches the mean free path of fluid molecules, the microflow effect, sometimes also referred to relative rarefaction effect, relative discrete effect or non-equilibrium effect, becomes pronounced. It was found often to enhance the flow rate. However, the surface roughness shows completely contrary influence. In order to clarify the influences of the two factors, a computer simulation work accompanied with theoretical analyses is conducted. Previous empirical models for Hydraulic Aperture which already containing roughness effect are modified with consideration of the microflow effect. Direct simulation using the lattice Boltzmann method is conducted on artificially created 2D fractures with random roughness following Gaussian distribution to reveal the competitive relationship of two effects. The simulation results also verify modified models. Among them, the one based on Rasouli and Hosseinian's model agrees with the simulation on the relationship between Hydraulic Aperture and mechanical Aperture for both cases with very rough fractures and relatively smooth fractures. Further investigation confirms that, under various roughness, the ratio of Hydraulic Aperture over mechanical Aperture shows quantitatively different trends as mechanical Aperture decreases. This phenomenon exists on a relatively wide scale. An equilibrium point of two effects is also found through analysis of the relationship. The results reveal the mechanism of microflow in 2D rough fractures and also provide a reference for engineering problems like the transport of natural gas through microfractures
Song Sha - One of the best experts on this subject based on the ideXlab platform.
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An Innovative Method to Evaluate Hydraulic Conductivity of a Single Rock Fracture Based on Geometric Characteristics
Rock Mechanics and Rock Engineering, 2020Co-Authors: Jie Tan, Guan Rong, Hongbin Zhan, Song ShaAbstract:Geometry of a single fracture has significant influence on the fluid flow in fractured rocks. However, quantification of geometry–flow relationship in a rock fracture is still far from being completed. The primary goal of this study was to identify a few key geometric parameters for quantifying its impact on fluid flow in a single rock fracture and then to evaluate its Hydraulic conductivity. The concept of a threshold Aperture is first introduced to estimate the effective area involved in the flow process in a single rock fracture. It is assumed that only those zones with greater Apertures than a threshold value are involved in the flow process. The effect of variable Aperture distributions on flow in a single rock fracture is quantified based on the cumulative distribution of individual Apertures of sampling points. The surface roughness is decomposed into primary roughness (i.e. the large-scale waviness of the fracture morphology) and secondary roughness (i.e. the small-scale unevenness) with a wavelet analysis. The influence of surface roughness on the fluid flow in a single rock fracture is quantified with the normalized area of primary roughness and the standard deviation of secondary roughness. By combining the variable Aperture distributions and the surface roughness on flow, an empirical equation to estimate the intrinsic Hydraulic Aperture and Hydraulic conductivity of a single rock fracture is proposed. In addition, a series of high-precision Hydraulic tests are conducted on 60 artificial tensile fractures to verify the proposed equation. The results show that the proposed equation predicts the intrinsic Hydraulic Aperture and Hydraulic conductivity of a single rock fracture very well.
