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  • 101.
    Wei, Jieqiang
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wu, Junfeng
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Molinari, Marco
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the modeling of neural cognition for social network applications2017In: 2017 IEEE Conference on Control Technology and Applications (CCTA), Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we study neural cognition in social network. A stochastic model is introduced and shown to incorporate two well-known models in Pavlovian conditioning and social networks as special case, namely Rescorla-Wagner model and Friedkin-Johnsen model. The interpretation and comparison of these model are discussed. We consider two cases when the disturbance is independent identically distributed for all time and when the distribution of the random variable evolves according to a Markov chain. We show that the systems for both cases are mean square stable and the expectation of the states converges to consensus.

  • 102. Widestrand, H.
    et al.
    Byegard, J.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Tullborg, E. L.
    Winberg, A.
    Andersson, P.
    Siitari-Kauppi, M.
    Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden): 1. Experimental setup and microscale characterization of retention properties2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 10Article in journal (Refereed)
    Abstract [en]

    [ 1] Mineralogical and retardation properties of rock materials responsible for water-rock interaction in in situ migration experiments with sorbing radioactive tracers were studied in laboratory experiments. The porosity was studied by water saturation measurements and the PMMA method was used for detailed porosity characterization of heterogeneity distributions and porosity profiles toward the fracture surface. Mylonite and altered diorite sampled in the rim zone of the fracture and representative bulk rock types were investigated by batch sorption measurements with crushed materials and through-diffusion and in-diffusion experiments in intact rock pieces. Autoradiography was used for visualization of in-diffusion profiles of sorbing tracers. The use of detailed porosity information and quantitative data on heterogeneity in porosity is shown to significantly improve the interpretation and evaluation of laboratory-scale diffusion experiments. We show through the combined approach of detailed porosity characterization and laboratory sorption and diffusion investigations that we can distinguish retention properties of bulk rock and altered rock and provide qualitative and quantitative data of heterogeneous rock properties that expand the possibility for including relevant processes in the interpretation of the results of in situ tracer tests.

  • 103. Zech, A.
    et al.
    Attinger, S.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Dietrich, P.
    Fiori, A.
    Rubin, Y.
    Teutsch, G.
    Is unique scaling of aquifer macrodispersivity supported by field data?2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 9, p. 7662-7679Article in journal (Refereed)
    Abstract [en]

    Spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity, which was found to be scale dependent. It increases with travel distance, stabilizing eventually at a constant value. However, the question of its asymptotic behavior at very large scale is still a matter of debate. It was surmised in the literature that macrodispersivity scales up following a unique scaling law. Attempts to define such a law were made by fitting a regression line in the log-log representation of an ensemble of macrodispersivities from multiple experiments. The functional relationships differ among the authors, based on the choice of data. Our study revisits the data basis, used for inferring unique scaling, through a detailed analysis of literature marcodispersivities. In addition, values were collected from the most recent tracer tests reported in the literature. We specified a system of criteria for reliability and reevaluated the reliability of the reported values. The final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship. On the contrary, our results indicate, that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value. Our investigation concludes that transport, and particularly the macrodispersivity, is formation-specific, and that modeling of transport cannot be relegated to a unique scaling law. Instead, transport requires characterization of aquifer properties, e.g., spatial distribution of hydraulic conductivity, and the use of adequate models.

  • 104. Zech, A.
    et al.
    Attinger, S.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Dietrich, P.
    Fiori, A.
    Rubin, Y.
    Teutsch, G.
    Reply to comment by S. Neuman on "Is unique scaling of aquifer macrodispersivity supported by field data?"2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 5, p. 4203-4205Article in journal (Other academic)
  • 105.
    Zech, Alraune
    et al.
    UFZ Helmholtz Ctr Environm Res, Permoserstr 15, D-04318 Leipzig, Germany..
    Attinger, Sabine
    UFZ Helmholtz Ctr Environm Res, Permoserstr 15, D-04318 Leipzig, Germany.;Univ Potsdam, Inst Earth & Environm Sci, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany..
    Bellin, Alberto
    Univ Trento, Dept Civil Environm & Mech Engn, Via Mesiano 77, I-38123 Trento, Italy..
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Dietrich, Peter
    UFZ Helmholtz Ctr Environm Res, Permoserstr 15, D-04318 Leipzig, Germany.;Univ Tubingen, Ctr Appl Geosci, Holderlinstr 12, D-72074 Tubingen, Germany..
    Fiori, Aldo
    Roma Tre Univ, Dept Engn, Via Volterra 62, I-00146 Rome, Italy..
    Teutsch, Georg
    UFZ Helmholtz Ctr Environm Res, Permoserstr 15, D-04318 Leipzig, Germany..
    Dagan, Gedeon
    Tel Aviv Univ, Sch Mech Engn, IL-69978 Ramat Aviv, Israel..
    A Critical Analysis of Transverse Dispersivity Field Data2019In: Ground Water, ISSN 0017-467X, E-ISSN 1745-6584, Vol. 57, no 4, p. 632-639Article in journal (Refereed)
    Abstract [en]

    Transverse dispersion, or tracer spreading orthogonal to the mean flow direction, which is relevant e.g, for quantifying bio-degradation of contaminant plumes or mixing of reactive solutes, has been studied in the literature less than the longitudinal one. Inferring transverse dispersion coefficients from field experiments is a difficult and error-prone task, requiring a spatial resolution of solute plumes which is not easily achievable in applications. In absence of field data, it is a questionable common practice to set transverse dispersivities as a fraction of the longitudinal one, with the ratio 1/10 being the most prevalent. We collected estimates of field-scale transverse dispersivities from existing publications and explored possible scale relationships as guidance criteria for applications. Our investigation showed that a large number of estimates available in the literature are of low reliability and should be discarded from further analysis. The remaining reliable estimates are formation-specific, span three orders of magnitude and do not show any clear scale-dependence on the plume traveled distance. The ratios with the longitudinal dispersivity are also site specific and vary widely. The reliability of transverse dispersivities depends significantly on the type of field experiment and method of data analysis. In applications where transverse dispersion plays a significant role, inference of transverse dispersivities should be part of site characterization with the transverse dispersivity estimated as an independent parameter rather than related heuristically to longitudinal dispersivity.

  • 106. Zou, L.
    et al.
    Frampton, A.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Impacts of dead-ends on flow and transport in fractured rocks2018In: 2nd International Discrete Fracture Network Engineering Conference, DFNE 2018, American Rock Mechanics Association (ARMA) , 2018Conference paper (Refereed)
    Abstract [en]

    Detailed simulation of flow and transport through a rough-walled fracture-matrix system with fracture dead-ends is performed. The analysis demonstrates a significant impact of fracture dead-ends on fluid flow and solute transport processes in the modelled system. Two 2D representative rock fracture-matrix models with and without fracture dead-ends are constructed based on high-resolution laser-scanned measurements of a granite rock fracture surface. Simulations of flow and transport with three Péclet numbers (Pe) ranging from 0.1 to 10 are conducted using a code implementing the finite volume method (FVM) to solve the Navier-Stokes equations (NSE) for water flow in the fracture, and the advection-diffusion equation (ADE) is adopted to solve for transport in the whole fracture-matrix system, also accounting for matrix diffusion. The features of the velocity fields and evolution of concentration distributions as well as breakthrough curves of the two modelled cases are presented and analyzed, with results showing that fracture dead-ends significantly affect solute transport processes and cause important retardation of transport in the fracture. This indicates that overly conservative assessments of solute mass arrivals may be made when fracture dead-ends are ignored in discrete fracture network modelling.

  • 107.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Modeling of advection-dominated transport in rough-walled rock fractures: a comparison of Reynolds and Navier-Stokes equationsManuscript (preprint) (Other academic)
    Abstract [en]

    Statistical analysis of flow-dependent specific surface areas of a 3D rough-walled fracture-matrix system were presented in this paper, based on numerical simulations of fluid flow and advective particle transport. The aim is to investigate the flow-dependent solute transport quantities in natural fracture-matrix systems, and identify the potential uncertainty lie in the common used flow model (i.e., Reynolds equation) by comparing with the more realistic flow model(i.e., Navier-Stokes equations). The rough-walled fracture model was built from laser-scanned surface tomography of a real rock sample, by considering realistic features of surfaces roughness and asperity contacts. Based on the flow fields simulated by solving the Reynolds and Navier-Stokes equations, the advective transport was modeled through Lagrangian particle tracking. The controlling quantities of advective transport in fracture-matrix systems (i.e., residence time, transport resistance and specific surface area) were statistically analyzed and compared. The results generally show that fracture surface roughness and associated spatially variable apertures as well as shear caused asperity contacts significantly increase the heterogeneity of flow field in rough-walled fractures, which consequently affects the flow-dependent transport process. By comparison, the simplified flow model (i.e., Reynolds equation) may cause uncertainty in quantifying of the specific surface area for the realistic rough-walled fracture-matrix systems. To identify such uncertainty, it is important to obtain the more reliable flow fields by solving the NSE. The presented results are helpful in uncertainty quantification and risk assessment of solute transport in natural fractured rocks.

  • 108.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    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.
    Roughness decomposition and effects on fluid flow in single rock fractures2014In: ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014, International Society for Rock Mechanics , 2014, p. 457-465Conference paper (Refereed)
    Abstract [en]

    The rock fractures usually consist of surfaces with different orders or scales of roughness, which have critical effects on the fluid flow behavior inside the fractures. In this paper, a two dimensional representative single rock fracture model was built, based on a laser scanned data of rock surface of granite. The surfaces roughness of the fracture was then quantitively decomposed into several levels of surface roughness by applying the wavelet analysis. A self-developed Finite Volume Method solver was then applied to solve the Navier-Stokes equations for numerical modelling of fluid flow in the fracture models formatted with four levels of decomposed roughness, respectively, with different Reynolds numbers varying from 0.001 to 1000.0. Then, the features of velocity profiles and the effective hydraulic apertures at each level of rough fractures decomposition and Reynolds numbers were calculated and analyzed. The results show that when the Reynolds number is small (less than 10.0), the effective hydraulic aperture slightly increase nearly linearly with the decomposed roughness levels. When the Reynolds number is large, the effective hydraulic apertures decrease dramatically, and the non-linear flow behaviors represented by expansion of the eddy flow regions caused by roughness: The larger extent of high-frequency roughness, the more obvious and complicate eddy flow regions yielded.

  • 109.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Impact of Normal Stress Caused Closure on Fluid Flow and Solute Retention in Rock Fractures2018Conference paper (Refereed)
    Abstract [en]

    Modeling of coupled hydro-mechanical and chemical (HMC) processes in fractured rocks is an important topic for many geoengineering projects.  Over the past decades, many efforts have been devoted to study the flow and transport in single fractures with consideration of mechanical effects. It is generally known that the mechanical effects, i.e. normal and shear deformation, significantly affect fluid flow and solute transport processes in rough-walled rock fractures since the deformation may largely alter the structure of fracture apertures that directly controls transmissivity. Due to complicated physical processes combined with complexity of geometry structures, many issues remain open questions, such as fracture surface roughness characterization, deformation dependence of transmissivity and advective transport in natural rock fractures. In this work, we attempt to investigate the impact of stress caused closure on fluid flow and solute advective transport in a rough-walled fracture through numerical modeling.  A rough-walled fracture model is created based on a laser-scanned rock surface. The Bandis’s model is used to describe the fracture closure subject to normal stress. The flow is modeled by solving Reynolds equation and the advective transport is simulated through Lagrangian particle tracking. The results show that the normal stress caused fracture closure creates asperity contacts and reduces the mean aperture, which significantly reduces transmissivity, and affects the travel time and transport resistance. With increases of normal stress, the specific surface area reduces nonlinearly due to the nonlinear closure. In practice, especially for important hydrogeological projects, e.g. nuclear waste disposal, it is important to consider the coupled HMC processes in design and risk assessment.

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  • 110.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, U.
    KTH.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Impacts of elastic jacking on rock grouting2018In: ISRM International Symposium - 10th Asian Rock Mechanics Symposium, ARMS 2018, International Society for Rock Mechanics , 2018Conference paper (Refereed)
    Abstract [en]

    The injection pressure is an important design and operational parameter in rock grouting since it controls the grout penetration length and may cause harmful mechanical deformation of the rock mass, such as opening/dilation of the fractures, referred to as jacking. At present, modeling of rock grouting mainly relies on analytical models where the impact of jacking on the grout penetration in rock fractures is not considered. In this study, we present a hydro-mechanical coupled model for rock grouting in a single one-dimensional rock fracture, with consideration of jacking and two-phase flow, i.e. cement grout and groundwater. It assumes that the cement grouts are Bingham fluids and that the rock matrix is an elastic material. The fracture is simplified as a pair of smooth parallel plates. A finite element method (FEM) code is developed to iteratively solve the two-phase flow in the fracture and the elastic deformation of the rock matrix. Two cases with and without consideration of jacking are simulated and compared. The results generally show that jacking of fractures significantly affects the grout penetration in the fracture, which should be properly considered in modeling of rock grouting. This numerical model is able to describe more realistic physical processes in rock grouting, which can be used to estimate the optimal injection pressure in practice. 

  • 111.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Skanska AB, Stockholm.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Cement grout propagation in 2D fracture networks: impact of rheology2019In: Proceedings in Earth and Geosciences: Rock Mechanics for Natural Resources and Infrastructure Development / [ed] Sergio A.B. da Fontoura, Ricardo Jose Rocca, José Pavón Mendoza, CRC Press, 2019, Vol. 6, p. 2486-2493Conference paper (Refereed)
    Abstract [en]

    Cement grouts propagation into a two-dimensional water-saturated fracture networks with different values of rheological properties are simulated by using an extended two-phase flow model. The cement grouts are typical non-Newtonian fluids that contain yield stress, which are often assumed as Bingham fluids. The aim of this study is to investigate the impact of Bingham rheological properties, i.e. yield stress and plastic viscosity, on cement gouts propagation in two-dimensional fracture networks. The results generally show that the rheological properties of cement grouts, i.e. yield stress and plastic viscosity, significantly affect cement grouts propagation in the fracture network. The propagation rate in the fracture networks reduces with the increase of the yield stress and the plastic viscosity of the cement grouts.

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    Cement grout propagation in 2D fracture networks: impact of rheology
  • 112.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Cement grout propagation in two-dimensional fracture networks: Impact of structure and hydraulic variability2019In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 115, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Analysis of cement grout propagation in water-saturated two-dimensional discrete fracture networks is presented in this study. A two-phase flow model for Bingham fluids flow in a single saturated fracture is extended to simulate cement grouts propagation in saturated networks. Using this extended model, the impacts of network structure and hydraulic variability, i.e., network geometry and aperture distribution, on the propagation process are investigated through numerical simulations. Cement grout propagation in 50 realizations of a two-dimensional discrete fracture network (2D DFN) are simulated with different cases of aperture variability, i.e. constant aperture, uncorrelated and length-correlated heterogeneous apertures following a truncated lognormal distribution. The results indicate that network structure and hydraulic variability significantly affect the grout propagation in 2D DFN systems. The randomized network structure and uncorrelated heterogeneous apertures significantly delay the propagation rate and largely increase the variability range of the propagation volume fraction. In contrast, in the case with length-correlated heterogeneous apertures, the propagation rate increases, while the variability range and rate of change of the propagation volume fraction decreases. The extended two-phase flow model for fracture networks and the simulation results presented in this work are useful for basic understanding of the processes relevant for design, monitoring and execution of rock grouting.

  • 113.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Skanska AB, Stockholm.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Characterization of effective transmissivity for cement grout flow in rock fractures2019In: Proceedings of Nordic Grouting Symposium 2019, 2019Conference paper (Refereed)
    Abstract [en]

    Cement grouting has been widely used in rock engineering. Proper characterization of the effective transmissivity for cement grout flow in rock fractures is primarily important for the design of rock grouting. In practice, the hydraulic transmissivity of groundwater flow in rock fractures characterized by hydraulic tests, i.e., pumping or slug test, is often used for the design of rock grouting. However, cement grouts used in rock grouting practice are typical non-Newtonian fluids contain yield stress, which has different effective transmissivity from the Newtonian groundwater. Therefore, using the groundwater transmissivity characterized by hydraulic tests may cause significant uncertainty in modeling and design of cement rock grouting. In this study, we focus on the effective transmissivity of non-Newtonian cement grout flow in a single fracture, aiming to illustrate the difference between the effective transmissivity of non-Newtonian cement grouts and the hydraulic transmissivity of the Newtonian groundwater. The cement grout is assumed as a Bingham fluid. The theoretical solution for the effective transmissivity of Bingham grout for homogeneous fractures is presented. This solution is compared with the theoretical hydraulic transmissivity, i.e., the cubic law. The results generally illustrate the significant differences between the effective transmissivity of non-Newtonian cement grouts and the hydraulic transmissivity of groundwater. The effective transmissivity of non-Newtonian cement grout is nonlinear which a function of injection pressure. Using the hydraulic transmissivity for rock grouting may underestimate the propagation length of the cement grout in rock fractures. The obtained result is helpful for rock grouting design in practice to reduce the potential uncertainties caused by using the hydraulic transmissivity.

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  • 114.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Modeling of rock grouting in saturated variable aperture fractures2018In: Proceedings of Bergdagarna 2018., 2018, p. 79-87, article id 10Conference paper (Refereed)
    Abstract [en]

    Modeling and analysis of cement grouts flow in rock fractures is important in the design, execution and monitoring of grouting in fractured rocks. At present, modeling of rock grouting mainly relies on analytical models, e.g., the real time grouting control (RTGC) method. In the RTGC method, it is assumed that the rock fractures are consisting of smooth parallel plates or disks and water flow is neglected. However, in reality, the natural rock fractures are commonly consisting of complex rough-walled surfaces and are filled with groundwater; therefore, grouting is actually a multiphase (non-Newtonian grouts and groundwater) flow process in rough-walled rock fractures with variable apertures. In this study, we present an efficient one-dimensional (1D) numerical model for modeling of rock grouting in a single rock fracture with consideration of multiphase flow and variable apertures. It is assumed that the cement grouts are Bingham fluids and that the analytical solution for flowrate with a given pressure gradient in a pair of smooth parallel plates is locally applicable. A time-dependent advection equation is used to describe the interface (between the grout and groundwater) propagation. A finite element method (FEM) code is developed to iteratively solve the mass balance and the interface advection equations. The numerical simulations are compared with the RTGC method. It generally shows that water flow significantly affect grouts penetration in the fracture, especially for the grouts with relatively lower viscosity. The variable aperture significantly postpones the penetration process compared with that of constant aperture. This numerical model is able to describe more realistic physical processes and geometry conditions in rock grouting, which can be readily used in practice to reduce the potential uncertainties in application of simplified analytical models.

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    Modeling of rock grouting in saturated variable aperture fractures
  • 115.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Non-Newtonian fluid flow in 2D fracture networks2017Conference paper (Refereed)
    Abstract [en]

    Modeling of non-Newtonian fluid (e.g., drilling fluids and cement grouts) flow in fractured rocks is of interest in many geophysical and industrial practices, such as drilling operations, enhanced oil recovery and rock grouting. In fractured rock masses, the flow paths are dominated by fractures, which are often represented as discrete fracture networks (DFN). In the literature, many studies have been devoted to Newtonian fluid (e.g., groundwater) flow in fractured rock using the DFN concept, but few works are dedicated to non-Newtonian fluids.In this study, a generalized flow equation for common non-Newtonian fluids (such as Bingham, power-law and Herschel-Bulkley) in a single fracture is obtained from the analytical solutions for non-Newtonian fluid discharge between smooth parallel plates. Using Monte Carlo sampling based on site characterization data for the distribution of geometrical features (e.g., density, length, aperture and orientations) in crystalline fractured rock, a two dimensional (2D) DFN model is constructed for generic flow simulations. Due to complex properties of non-Newtonian fluids, the relationship between fluid discharge and the pressure gradient is nonlinear. A Galerkin finite element method solver is developed to iteratively solve the obtained nonlinear governing equations for the 2D DFN model. Using DFN realizations, simulation results for different geometrical distributions of the fracture network and different non-Newtonian fluid properties are presented to illustrate the spatial discharge distributions. The impact of geometrical structures and the fluid properties on the non-Newtonian fluid flow in 2D DFN is examined statistically. The results generally show that modeling non-Newtonian fluid flow in fractured rock as a DFN is feasible, and that the discharge distribution may be significantly affected by the geometrical structures as well as by the fluid constitutive properties.

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    Non-Newtonian fluid flow in 2D fracture networks
  • 116.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Skanska AB .
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Non-Newtonian grout flow in single rough-walled rock fractures2019Conference paper (Refereed)
    Abstract [en]

    Modeling of cement grout flow in rock fractures plays an important role in the design of rock grouting. Cement grouts used in rock grouting practice are typical non-Newtonian fluids containing yield stress, and are often assumed as Bingham fluids. Natural rock fractures typically consist of rough surfaces. Therefore, in reality, rock grouting process actually involves non-Newtonian fluid flow in rough-walled fractures, which is rarely studied in the literature. In this work, we focus on the impact of surface roughness and present direct numerical simulations of non-Newtonian grouts flow in single rough-walled fractures, using a regularized method to approximate the yield-stress. The rough-walled rock fracture models are created from a laser-scanned surface of a granite rock sample, to represent realistic features of natural rock fractures. The numerical results generally show nonlinear behaviors of non-Newtonian fluid flow in rough-walled fractures. The surface roughness significantly reduces the effective transmissivity when Reynolds number is relatively large. The obtained result can be used for upscaling analysis in practice, in order to reduce the potential uncertainties caused by the surface roughness of the rock fractures.

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  • 117.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Two-phase cement grout propagation in homogeneous water-saturated rock fractures2018In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 106, p. 243-249Article in journal (Refereed)
    Abstract [en]

    Modeling of cement grout flow in rock fractures is important for the design, monitoring and execution of rock grouting that is widely used in a variety of rock engineering applications. This study presents a mathematical model based on the Reynolds flow equation for cement grout flow in a homogeneous water-saturated rock fracture. The model is based on two-phase flow, i.e. grout as a Bingham fluid and groundwater as a Newtonian fluid, and is used for investigating the importance of the water phase in rock grouting. The modeling results for the two-phase flow generally show the importance of the water phase that can significantly affect the pressure distribution and grout penetration in the fracture, especially under the condition of grout hardening. Such effects depend on the viscosity ratio between the grout and groundwater, which becomes increasingly important for cases with smaller values of the viscosity ratio. The grout density also affects the grout penetration length. Applying an analytical solution based on single-phase flow, i.e. neglecting the impact of groundwater flow, for modeling grout injection, will generally overestimate the penetration length.

  • 118.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Yield-power-law fluid propagation in water-saturated fracture networks with application to rock grouting2020In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 95, article id 103170Article in journal (Refereed)
    Abstract [en]

    Cement grouting is widely applied in rock tunneling and underground construction to reduce groundwater inflow and increase the tightness of rock masses. The rock grouting process involves complex non-Newtonian grouts propagation in fracture networks. In this study, a two-phase flow model extended for yield-power-law fluid (e.g., cement grout) propagation in water-saturated fracture networks is presented. The effective transmissivity is scaled from analytical solutions for single-phase yield-power-law fluids flow between a pair of smooth parallel plates. This extended two-phase flow model for fracture networks is verified based on a unique set of experimental data. The full experiment dataset is presented in this work for the first time. Impacts of rheological parameters and time-dependent rheological properties of injected yield-power-law fluids on propagation processes are investigated through numerical simulations. A measure referred to as the propagation volume fraction is defined as an indicator of the propagation process. The results generally show that the rheological properties significantly affect the evolution of the propagation volume fraction. The propagation rate reduces with increased yield stress, consistency index and flow index. The two-phase flow of yield-power-law fluid propagation in a heterogeneous fracture network is also simulated, showing that the heterogeneity of fracture apertures may significantly affect the propagation process. For the heterogeneous case, with two-point distribution of apertures, the propagation volume fraction can be represented by using the harmonic mean aperture. Since the yield-power-law constitutive model covers a wide range of non-Newtonian fluids, the results presented in this work can be used for studying non-Newtonian fluid propagation in a variety of homogeneous or heterogeneous fracture networks, which can be used for rock grouting design.

  • 119.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Assumptions of the analytical solution for solute transport in a fracture-matrix system2016In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 83, p. 211-217Article in journal (Refereed)
  • 120.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Effect of sorption on solute transport in a single rough rock fracture2017In: 13th ISRM International Congress of Rock Mechanics, International Society for Rock Mechanics , 2017Conference paper (Refereed)
    Abstract [en]

    Sorption process plays a significant role for solute retardation in rock fractures. In this paper, for the aim to investigate the effect of sorption on solute transport in a single rough fracture, a 2D model of representative single rock fracture was built and its roughness was statistically characterized based on the measured data of rock surface topography by laser scanning. A Finite Volume Method (FVM) code was developed to solve the Navier-Stokes (NS) equations and transport equation for numerical modelling the process of fluid flow and solute transport in the rock fracture model. Two groups of simulations were conducted: with and without the consideration of the sorption process with different average flow velocities. The results show that the surface roughness increased the complexities of flow fields, and the non-linear sorption process plays a significant role in the retardation of solute transport through rock fractures. The sorption process caused an obvious lagging time in both the solute concentration fields (plumes) and corresponding breakthrough curves. This lagging time increases with the distance from the inlet boundary, and relatively decreases with the increase of mean velocities.

  • 121.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Effects of multi-level surface roughness on solute transport in single rock fractures2016In: The proceeding of International Symposium on Reducing Risks in Site Investigation, Modeling and Construction for Rock Engineering, 2016Conference paper (Refereed)
    Abstract [en]

    Natural rock fractures are consisted of complicate rough surfaces with multi-level surface roughness which causes significant uncertainties in fluid flow and solute transport be-haviors through fractured rocks. In this study, for the aim of investigation the effects of multi-level surface roughness on fluid flow and solute transport in rock fractures, a single rough-walled fracture model was built from a scanned granite rock surface, which was then gradually decomposed and characterized by wavelet analysis and statistics. A verified finite volume method (FVM) code was used to simulate fluid flow and solute transport in the rough fracture models by solving the Navier-Stokes equations (NSE) and advection-dispersion equation (ADE). The simulation results of nonlinear flow and solute breakthrough curves (BTCs) showed that the multi-level surface roughness strongly correlated with the Eddy flows and the solute non-Fickian transport behaviors, represented by the changes of effective advective flow apertures and an empirical function of the BTCs. The results would improve our understanding of solute transport in fractured rocks and may help to reduce the uncertainties and risks in related engi-neering practices.

  • 122.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Effects of Sorption on Solute Transport in a Single Rough Rock Fracture2015Conference paper (Refereed)
    Abstract [en]

    The sorption process plays a significant role in the retardation of solute transport through the fractures. In this paper, based on the measured data of rock surfaces by laser scanning, a 2D geometry model of a representative single rock fracture was built and its roughness was statistically characterized, and a Finite Volume Method (FVM) code was developed and applied to solve the NS equation and transport equation for numerical modelling the process of fluid flow and solute transport. Two groups of simulation were then calculated: with and without the consideration of the sorption process, with different average flow velocities. The effects of sorption on the solute transport process were then analyzed, discussed and followed by concluding remarks on the sorption impact on the understanding of mass transport process in fractured rock masses.

  • 123.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Invasion flow enhanced solute mixing at rough-walled rock fracture intersectionsManuscript (preprint) (Other academic)
    Abstract [en]

    The processes of fluid flow and solute transport through rock fractures are of primary importance in environmental engineering and geosciences. This study presented numerical modeling results of fluid flow and solute transport in a 3D rock fracture-matrix system with an orthogonal intersection of two rough-walled rock fractures. The rough-walled fracture geometry models were built from laser-scanned data of a real rock surface, for a realistic representation of natural rock fracture surface roughness. The fluid flow in the two intersected fractures and solute transport in the fracture-matrix system were simulated by solving the Navier-Stokes equations (NSE) and transport equation in the entire system. The dependence of mixing on Péclet number (Pe), flow directionality and interaction with matrix diffusion were analyzed. The results showed important invasion flow patterns that significantly enhanced the solute mixing process, which cannot be described by traditional complete mixing and streamline routing models. It also cannot be simulated by simplified 2D geometry models ignoring the surface roughness as widely used in previous published studies. The finding of invasion flow and associated impacts on mixing in this study is particularly important in prediction of solute transport in natural fractured rocks, especially when discrete fracture network (DFN) approach is applied.

    Download full text (pdf)
    Invasion flow enhanced solute mixing at rough-walled rock fracture intersections
  • 124.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Modeling of flow and mixing in 3D rough-walled rock fracture intersections2017In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 107, p. 1-9Article in journal (Refereed)
    Abstract [en]

    The processes of fluid flow and solute transport through rock fractures are of primary importance in environmental engineering and geosciences. This study presented numerical modeling results of fluid flow and solute transport in a 3D rock fracture-matrix system with an orthogonal intersection of two rough-walled rock fractures. The rough-walled fracture geometry models were built from laser-scanned data of a real rock surface, for a realistic representation of natural rock fracture surface roughness. The fluid flow in the two intersected fractures and solute transport in the fracture-matrix system were simulated by solving the Navier–Stokes equations (NSE) and transport equation in the entire system. The dependence of mixing on Péclet number (Pe) and flow directionality features were analyzed. The results directly visualized important channeling flow patterns that significantly enhanced the solute mixing process at the rough-walled fracture intersection. The illustrated channeling flow and associated impacts on mixing are particularly important in the prediction of solute transport in natural fractured rocks, especially when discrete fracture network (DFN) approach is applied.

  • 125.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Modeling of solute transport in a 3D rough-walled fracture-matrix systemManuscript (preprint) (Other academic)
    Abstract [en]

    Fluid flow and solute transport in a 3D rough-walled fracture-matrix system was simulated by directly solving the Navier-Stokes equations for fracture flow and solving the transport equation for the whole domain of fracture and matrix with considering matrix diffusion. The rough-walled fracture-matrix model was built from laser-scanned surface tomography of a real rock sample, by considering realistic features of surfaces roughness and asperity contacts. The numerical modeling results were compared with both analytical solutions based on simplified fracture surface geometry and numerical results by particle tracking based on the Reynolds equation. The aim is to investigate impacts of surface roughness on solute transport in natural fracture-matrix systems, and to quantify the uncertainties in application of simplified models. The results show that fracture surface roughness significantly increases heterogeneity of velocity field in the rough-walled fractures, which consequently cause complex transport behavior, especially the dispersive distributions of solute concentration in the fracture and complex concentration profiles in the matrix. Such complex transport behavior caused by surface roughness are important sources of uncertainty that needs to be considered for modeling of solute transport processes in fractured rocks. The presented direct numerical simulations of fluid flow and solute transport serve as efficient numerical experiments that provide reliable results for the analysis of effective transmissivity as well as effective dispersion coefficient in rough-walled fracture-matrix systems. Such analyses are helpful in model verifications, uncertainty quantifications and design of laboratorial experiments.

    Download full text (pdf)
    Modeling of solute transport in a 3D rough-walled fracture-matrix system
  • 126.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Modeling of Solute Transport in a 3D Rough-Walled Fracture-Matrix System2017In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 116, no 3, p. 1005-1029Article in journal (Refereed)
    Abstract [en]

    Fluid flow and solute transport in a 3D rough-walled fracture-matrix system were simulated by directly solving the Navier-Stokes equations for fracture flow and solving the transport equation for the whole domain of fracture and matrix with considering matrix diffusion. The rough-walled fracture-matrix model was built from laser-scanned surface tomography of a real rock sample, by considering realistic features of surfaces roughness and asperity contacts. The numerical modeling results were compared with both analytical solutions based on simplified fracture surface geometry and numerical results by particle tracking based on the Reynolds equation. The aim is to investigate impacts of surface roughness on solute transport in natural fracture-matrix systems and to quantify the uncertainties in application of simplified models. The results show that fracture surface roughness significantly increases heterogeneity of velocity field in the rough-walled fractures, which consequently cause complex transport behavior, especially the dispersive distributions of solute concentration in the fracture and complex concentration profiles in the matrix. Such complex transport behaviors caused by surface roughness are important sources of uncertainty that needs to be considered for modeling of solute transport processes in fractured rocks. The presented direct numerical simulations of fluid flow and solute transport serve as efficient numerical experiments that provide reliable results for the analysis of effective transmissivity as well as effective dispersion coefficient in rough-walled fracture-matrix systems. Such analysis is helpful in model verifications, uncertainty quantifications and design of laboratorial experiments.

  • 127.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Roughness decomposition and nonlinear fluid flow in a single rock fracture2015In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 75, p. 102-118Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to investigate the effects of wall surface roughness on fluid flow through rock fractures. A wavelet analysis technique was developed to define a mathematical criterion for decomposing the original wall surface roughness profiles of a fracture into a high-frequency (secondary roughness) profile and a low-frequency (primary roughness) profile, in order to examine their impacts on fluid flow, by solving the Navier-Stokes equations (NSE) without linearization, using a self-developed 2D finite volume method (FVM) code. The results indicate that the high-frequency secondary roughness is the main cause for dynamic evolution of Eddy flow regions in the fracture flow field, besides the Reynolds number (Re). In the original fracture model with the high-frequency secondary roughness, our results show that fluid flow fields are not only generally non-linear, but also with non-stop generation and motions of eddies in the boundary layer regions of rough fractures when the Re = 1000 in this study, which will affect the solute transport processes in fractured rock masses. The complete NSE were solved without removing acceleration and inertial terms, so that the impacts of surface roughness on the nonlinear and dynamic flow behavior of rock fractures were calculated and visualized more accurately, which is important for modeling mass and energy transport processes in fractures and fractured rock masses.

  • 128.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Shear enhanced nonlinear flow in rough-walled rock fracturesManuscript (preprint) (Other academic)
    Abstract [en]

    Nonlinear flow in 3D rough-walled rock fracture models are simulated by solving the Navier-Stokes equations in this paper. The emphasis is on the impacts of shear caused aperture changes (variable apertures and asperity contacts) and flow conditions (inertial term) upon nonlinear flow behaviors in 3D rough-walled rock fractures. In order to compare shear effects, two 3D fracture models, with and without shear process, were established with the identical initial rough-walled surfaces tomography of a realistic rock sample. Five groups of simulations with different inflow boundary conditions of flowrates/Reynolds numbers (Re) were conducted to demonstrate shear enhanced nonlinearity of flow fields and limitations of local cubic law (LCL) approach. The flow results clearly show channeling flow along the preferential fluid paths, transverse flow around the contact spots and eddy flows behind contact spots with increasing Re numbers, which cannot be observed in 2D models. The effective transmissivity of the 3D fracture model was calculated from the modeling results of velocity and pressure fields. The results showed that the effective transmissivity is a function of local apertures with important uncertainties even when Re is small (i.e. Re = 0.4 in this study), thus the validity of the transmissivity evaluation using LCL approach for nonlinear flow in 3D rough-walled rock fractures is questionable. The mechanical effects, i.e. stress and shear caused aperture space changes and asperity contacts should be considered for modeling flow and mass/energy transport processes in rough-walled fractures in 3D.

    Download full text (pdf)
    Shear enhanced nonlinear flow in rough-walled rock fractures
  • 129.
    Zou, Liangchao
    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.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Shear-enhanced nonlinear flow in rough-walled rock fractures2017In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 97, p. 33-45Article in journal (Refereed)
    Abstract [en]

    Nonlinear flow in 3D rough-walled rock fractures is simulated by solving the Navier-Stokes equations. The emphasis is on the impact of shear-caused aperture changes (variable apertures and asperity contacts) and flow conditions (inertial term) upon nonlinear flow behavior. In order to compare shear effects, two 3D fracture models, with and without shear, were established with identical initial rough-walled surfaces topographies of a realistic rock sample. Five groups of simulations with different inflow boundary conditions of flowrates/Reynolds numbers (Re) were conducted to demonstrate shear-enhanced nonlinearity of flow fields and limitations of local cubic law (LCL) approach. The flow results clearly show channeling flow along the preferential paths, transverse flow around the contact spots, and eddy flows behind contact spots with increasing Re, which cannot be observed in 2D models. The effective transmissivity of the 3D fracture model was calculated from the modeling results of velocity and pressure fields. The results showed that the effective transmissivity is a function of local apertures with important uncertainties even when Re is small (i.e. Re = 0.4 in this study), thus the validity of the transmissivity evaluation using LCL approach for nonlinear flow in 3D rough-walled rock fractures is questionable.

  • 130.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Li, B.
    Mo, Y.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    A High-Resolution Contact Analysis of Rough-Walled Crystalline Rock Fractures Subject to Normal Stress2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Refereed)
    Abstract [en]

    Analysis of rock fracture deformation by normal stress is important for quantifying hydromechanical properties of fractured rocks that are related to a large number of geophysical problems and geoengineering applications. Experimental and numerical results for the closure of crystalline rock fractures subject to normal stress are presented in this study. An efficient high-resolution, half-space elastic–plastic contact model for analyzing the closure of crystalline rock fractures based on the Boussinesq’s solution is validated by high-precision and high-resolution experimental data. Using the validated elastic–plastic model, we investigate the correlation between fracture-specific stiffness and multi-scale surface roughness. The wavelet analysis method and the extended averaged slope magnitude for asperity heights (referred to as Z23D) are introduced to characterize the multi-scale surface roughness. The results show that the elastic–plastic contact model is effective and precise in modeling the closure of crystalline rock fractures, which matches better with the test results than the elastic model. The multi-scale features of surface roughness can be well characterized by the wavelet analysis and the extended roughness parameter Z23D. The specific stiffness is nonlinearly correlated with the multi-scale surface roughness that possibly follows a power law. The validated elastic–plastic contact model and the multi-scale surface roughness characterization methods, as well as the nonlinear correlation between the specific stiffness and the multi-scale surface roughness presented in this study, are helpful for evaluating the dependence of mechanical behaviors of rock fractures on its multi-scale surface roughness.

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