kth.sePublications
Change search
Refine search result
123 1 - 50 of 116
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed thermal response tests: New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.

    Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.

    A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.

    The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO2 as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO2 may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.

    Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.

    Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.

    At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.

    Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.

    Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N2, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.

    Download full text (pdf)
    José Acuña - Doctoral Thesis
  • 2. Al-Yaarubi, A. H.
    et al.
    Pain, C. C.
    Grattoni, C. A.
    Zimmerman, Robert W.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Navier-Stokes Simulations of Fluid Flow Through a Rock Fracture2013In: Dynamic Fluids and Transport Through in Fractured Rock, American Geophysical Union (AGU), 2013, p. 55-64Chapter in book (Other academic)
    Abstract [en]

    A surface profilometer was used to measure fracture profiles every 10 microns over the surfaces of a replica of a fracture in a red Permian sandstone, to within an accuracy of a few microns. These surface data were used as input to two finite element codes that solve the Navier-Stokes equations and the Reynolds equation, respectively. Numerical simulations of flow through these measured aperture fields were carried out at different values of the mean aperture, corresponding to different values of the relative roughness. Flow experiments were also conducted in casts of two regions of the fracture. At low Reynolds numbers, the Navier-Stokes simulations yielded transmissivities for the two fracture regions that were closer to the experimental values than were the values predicted by the lubrication model. In general, the lubrication model overestimated the transmissivity by an amount that varied as a function of the relative roughness, defined as the standard deviation of the aperture divided by the mean aperture. The initial deviations from linearity, for Reynolds numbers in the range 1-10, were consistent with the "weak inertia" model developed by Mei and Auriault for porous media, and with the results obtained computationally by Skjetne et al in 1999 on a two-dimensional self-affine fracture. In the regime 10 < Re < 40, both the computed and measured transmissivities could be fit very well to a Forchheimer-type equation, in which the additional pressure drop varies quadratically with the Reynolds number.

  • 3.
    Andersson, Johan Vium
    KTH, School of Architecture and the Built Environment (ABE).
    Undifferenced GPS for Deformation Monitoring2006Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    This thesis contains the development of a deformation monitoring software based on undifferenced GPS observations. Software like this can be used in alarm systems placed in areas where the earth is unstable. Systems like this can be used in areas where people are in risk of getting hurt, like in earthquake zones or in land slide areas, but they can also be useful when monitoring the movements in buildings, bridges and other artefacts.

    The main hypotheses that are tested are whether it is possible to detect deformations with undifferenced observations and if it is possible to reach the same accuracy in this mode as when working in a traditional mode where the observations are differenced.

    The development of a deformation monitoring software based on undifferenced GPS observations is presented. A complete mathematical model is given as well as implementation details. The software is developed in Matlab together with a GPS observation simulator. The simulator is mainly used for debugging purposes.

    The developed software is tested with both simulated and real observations. Results from tests with simulated observations show that it is possible to detect deformations in the order of a few millimetres with the software. Calculations with real observations give the same results. Further, the result from calculations in static mode indicates that the commercial software and the undifferenced software diverge a few millimetres, which probably depends on different implementations of the tropospheric corrections. In kinematic mode the standard deviation is about 1 millimetre larger in the undifferenced mode than in the double differenced mode. An initial test with different observation weighting procedures indicates that there is a lot of potential to improve the result by applying correct weights to the observations. This is one of the aims in the future work within this project.

    This thesis are sponsored by the Swedish Research Council for Enviroment, Agricultural Sciences and Spatial Planning, FORMAS within the framework “Monitoring of construction and detection of movements by GPS ref no. 2002-1257"

    Download full text (pdf)
    FULLTEXT01
  • 4.
    Bakyayita, Grace Kizito
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. Makerere Univ, Dept Civil & Environm Engn, Kampala, Uganda..
    Norrström, Ann-Catrine
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Kulabako, R. N.
    Makerere Univ, Dept Civil & Environm Engn, Kampala, Uganda..
    Assessment of Levels, Speciation, and Toxicity of Trace Metal Contaminants in Selected Shallow Groundwater Sources, Surface Runoff, Wastewater, and Surface Water from Designated Streams in Lake Victoria Basin, Uganda2019In: Journal of Environmental and Public health, ISSN 1687-9805, E-ISSN 1687-9813, article id 6734017Article in journal (Refereed)
    Abstract [en]

    The levels, speciation of elements, and toxicity of selected trace metals as well as other parameters in selected surface water, shallow groundwater sources, landfill leachate, and associated surface runoff in the Lake Victoria basin, Uganda, were studied. The WHO guidelines, Ugandan standards, Canadian guidelines and Swedish EPA were used for assessment. The shallow groundwater was acidic with pH values below 6.5. The pH, dissolved organic carbon, flouride, and sulphate levels for all springs were below the guideline values although 52.8% was contaminated with nitrates while 39% was contaminated with chloride ions. Some surface water samples had levels of major elements, such as iron, chromium, aluminium, and manganese, above the guideline values. Speciation studies showed that 74% of the metal ions was bound to dissolved organic matter in surface water, whereas in landfill leachates, the dominant ionic species was metal hydroxides or fulvic acid bound. Risk analysis based on the Swedish EPA showed varied risks of negative effects in 30%-76% of the sample sites ranging from high to increased risk in surface water, whereas the results from modelling sorption data using the Bio-met tool showed potential risk to toxicity effects of Cu2+, Ni2+, Zn2+, and Pb2+ in 15.3%-30.8% surface water samples and 8.3%-62.5% groundwater samples.

    Download full text (pdf)
    fulltext
  • 5. Boano, F.
    et al.
    Harvey, J. W.
    Marion, A.
    Packman, A. I.
    Revelli, R.
    Ridolfi, L.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications2014In: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 52, no 4, p. 603-679Article, review/survey (Refereed)
    Abstract [en]

    Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

  • 6.
    Bäckström, Ann
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    A study of impact fracturing and electric resistivity related to the Lockne impact structure, Sweden2005In: Impact Tectonics / [ed] Koeberl C; Henkel H, 2005, p. 389-404Conference paper (Refereed)
    Abstract [en]

    The fracture frequency and the electric resistivity of outcrops of crystalline basement rocks at the Lockne meteorite impact site have been studied in order to investigate the extent and radial changes of impact induced fracturing. By measuring the electric resistivity and the fracture frequency at the same outcrops, the effect of fracturing on the electric properties of the rock is estimated and correlated with the fracture frequency. A negative linear correlation between the Log of fracture frequency and the Log of electric resistivity was found.

    It was also found that the fracture frequency decreases in a transition zone over a distance of about 1100 m across the southern margin of the impact structure. A similar set of measurements was made across the suggested northern limit of the structure, but no change was detected. This implies that the outer limit of the Tandsbyn Breccia is further to the north. The studied area is, therefore, not likely to be the. margin of the structure.

  • 7.
    Bäckström, Ann
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Rock damage caused by underground excavation and meteorite impacts2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The intent of this thesis is to contribute to the understanding of the origin of fractures in rock. The man-made fracturing from engineering activities in crystalline rock as well as the fracturing induced by the natural process of meteorite impacts is studied by means of various characterization methods. In contrast to engineering induced rock fracturing, where the goal usually is to minimize rock damage, meteorite impacts cause abundant fracturing in the surrounding bedrock. In a rock mass the interactions of fractures on the microscopic scale (mm-cm scale) influence fractures on the mesoscopic scale (dm-m scale) as well as the interaction of the mesocopic fractures influencing fractures on the macroscopic scale (m-km scale). Thus, among several methods used on different scales, two characterization tools have been developed further. This investigation ranges from the investigation of micro-fracturing in ultra-brittle rock on laboratory scale to the remote sensing of fractures in large scale structures, such as meteorite impacts. On the microscopic scale, the role of fractures pre-existing to the laboratory testing is observed to affect the development of new fractures. On the mesoscopic scale, the evaluation of the geometric information from 3D-laser scanning has been further developed for the characterisation of fractures from tunnelling and to evaluate the efficiency of the tunnel blasting technique in crystalline rock. By combining information on: i) the overbreak and underbreak; ii) the orientation and visibility of blasting drillholes and; iii) the natural and blasting fractures in three dimensions; a analysis of the rock mass can be made. This analysis of the rock mass is much deeper than usually obtained in rock engineering for site characterization in relation to the blasting technique can be obtained based on the new data acquisition. Finally, the estimation of fracturing in and around two meteorite impact structures has been used to reach a deeper understanding of the relation between fracture, their water content and the electric properties of the rock mass. A correlation between electric resistivity and fracture frequency in highly fractured crystalline rock has been developed and applied to potential impact crater structures. The results presented in this thesis enables more accurate modelling of rock fractures, both supporting rock engineering design and interpretation of meteorite impact phenomena.

    Download full text (pdf)
    FULLTEXT01
  • 8.
    Bäckström, Ann
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Cosgrove, John W.
    Department of Earth Science and Engineering, Imperial College, London.
    Hudson, John A.
    Department of Earth Science and Engineering, Imperial College, London.
    Interpretation of the development of induced cracks within a pre-cracked rock microstructure and the similarities with the geometry of larger-scale geological fracturesIn: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201Article in journal (Other academic)
  • 9.
    Bäckström, Ann
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Feng, Quanhong
    Berg Bygg Konsult AB.
    Lanaro, Flavio
    Berg Bygg Konsult AB.
    Excavation Damage Zone (EDZ) at the TASQ tunnel (Äspö, Sweden): Quantification of blasting effects on the geological settings by 3D-laser-scanningIn: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917Article in journal (Other academic)
  • 10.
    Bäckström, Ann
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Feng, Quanhong
    Berg Bygg Konsult AB.
    Lanaro, Flavio
    Berg Bygg Konsult AB.
    Christiansson, Rolf
    Swedish Nuclear Fuel and Waste Management Co.
    Evaluation of the Excavation Damage Zone (EDZ) by using 3-D laser scanning technique2006In: The 4th Asian Rock Mechanics Symposium, Singapore, 8 - 10 November 2006, 2006Conference paper (Other academic)
  • 11.
    Bäckström, Ann
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Koyama, Tomofumi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    et al.,
    Numerical modelling of uniaxial compressive failure of granite with and without saline porewater2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 7, p. 1126-1142Article in journal (Refereed)
    Abstract [en]

    It is important for rock engineering design to be able to validate numerical simulations, i.e. to check that they adequately represent the rock reality. In this paper, the capability and validity of four numerical models is assessed through the simulation of an apparently simple case: the complete process of microstructural breakdown during the uniaxial compressive failure of intact crystalline rock. In addition to comparing the capabilities of the four models, the results generated by each model were compared with the experimentally determined complete stress-strain curves for the Swedish Avro granite for different porewater conditions. In this way, it has been possible to audit the models' adequacy for this particular simulation task. It was found that although the models had common features, they were each idiosyncratically different and required considerable expertise to match the actual stress-strain curves (which did not monotonically increase in axial strain)-indicating that, for more complex simulations, both adequate modelling and appropriate validation are not going to be an easy task. The work was conducted within the framework of the international 2004-2007 DEmonstration of COupled models and their VALidation against EXperiments with emphasis on Thermo Hydro Mechanic and Chemical aspects (DECOVALEX-THMC) phase on coupled modelling extended to include chemical effects and with application to the excavation damaged zone (EDZ) in crystalline rock.

  • 12. Bäckström, Ann
    et al.
    Lanaro, Flavio
    Berg Bygg Konsult AB.
    Christiansson, Rolf
    Swedish Nuclear Fuel and Waste Management Co.
    Coupled chemical-mechanical behaviour: the influence of salinity on the uniaxial compressive strength of the Smålands granite, Sweden2006In: Proc. of the 2nd International Conference on Coupled T-H-MC Processes in Geo-Systems: Fundamentals, Modeling, Experiments and Applications, Geo-Proc 2006, 2006, p. 437-443Conference paper (Refereed)
  • 13. Chan, T.
    et al.
    Christiansson, R.
    Boulton, G. S.
    Ericsson, L. O.
    Hartikainen, J.
    Jensen, M. R.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Stanchell, F. W.
    Vistrand, P.
    Wallroth, T.
    DECOVALEX III BMT3/BENCHPAR WP4: The thermo-hydro-mechanical responses to a glacial cycle and their potential implications for deep geological disposal of nuclear fuel waste in a fractured crystalline rock mass2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 805-827Article in journal (Refereed)
    Abstract [en]

    A number of studies related to past and on-going deep repository performance assessments have identified glaciation/ deglaciation as major future events in the next few hundred thousand years capable of causing significant impact on the long term performance of the repository system. Benchmark Test 3 (BMT3) of the international DECOVALEX III project has been designed to provide an illustrative example that explores the mechanical and hydraulic response of a fractured crystalline rock mass to a period of glaciation. The primary purpose of this numerical study is to investigate whether transient events associated with a glacial cycle could significantly influence the performance of a deep geological repository in a crystalline Shield setting. A conceptual site-scale (tens of kilometres) hydro-mechanical (HM) model was assembled based primarily on site-specific litho-structural, hydrogeological and geomechanical data from the Whiteshell Research Area in the Canadian Shield, with simplification and generalization. Continental glaciological modelling of the Laurentide ice sheet through the last glacial cycle lasting approximately 100,000 years suggests that this site was glaciated at about 60 ka and between about 22.5 and 11 ka before present with maximum ice sheet thickness reaching 2500 m and maximum basal water pressure head reaching 2000m. The ice-sheet/drainage model was scaled down to generate spatially and temporally variable hydraulic and mechanical glaciated surface boundary conditions for site-scale subsurface HM modelling and permafrost modelling. Under extreme periglacial conditions permafrost was able to develop down to the assumed 500-m repository horizon. Two- and three-dimensional coupled HM finite-element simulations indicate: during ice-sheet advance there is rapid rise in hydraulic head, high transient hydraulic gradients and high groundwater velocities 2-3 orders of magnitude higher than under nonglacial conditions; surface water recharges deeper than under nonglacial conditions; upon ice-sheet retreat, the gradients reverse; fracture zone network geometry, interconnectivity and hydraulic properties significantly influence flow domain response; residual elevated heads are preserved for 10,000s in the low-diffusivity rock; and no hydraulic jacking or shear failure occurs at depth. It was found that transient coupled modelling is necessary to capture the essence of glacial effects on Performance Assessment. Model dimensionality also significantly affects simulated results.

  • 14. Darcel, C.
    et al.
    Davy, P.
    Le Goc, R.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rock mass effective properties from a DFN approach2018In: 2nd International Discrete Fracture Network Engineering Conference, DFNE 2018, American Rock Mechanics Association (ARMA) , 2018Conference paper (Refereed)
    Abstract [en]

    Rock mass mechanical properties are strongly controlled by the fractures they contain. Their determination raises strong issues for many rock-engineering applications, like underground repository safety assessment, support design, slope stability or mine caving. To compensate the impossibility to perform direct in-situ measures of these properties at appropriate scales, empirical approaches classically aim to determine the rock mass equivalent properties from simple indicators. Here we propose an approach based on the complete representation of the rock mass as an intact rock with a population of discrete fractures through it (the Discrete Fracture Network). The core of the approach is the definition, at the rock mass scale, of the deformation induced by each fracture locally, including the fracture mechanical and geometrical parameters, the remote stress conditions and the interactions with the rest of the fracture population. Depending on the conditions, the resulting scaling and anisotropic effects can be critical. The method is applied to the Forsmark site in Sweden. We show that two main scaling regimes occur, where the shift from the one to the other is controlled by the ratio between the intact rock modulus, the typical fracture stiffness and the DFN size distribution. Beyond the scaling issue we quantify the resulting level of anisotropy. 

  • 15.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Setegn, Shimelis Gebriye
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Combined 3D Hydrodynamic and Watershed Modelling of Lake Tana, Ethiopia2011In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 398, no 1-2, p. 44-64Article in journal (Refereed)
    Abstract [en]

     The growing high demand for lake Tana water portends a disturbing future. The main objective of this paper is to make a contribution to the development of a sustainable use of the water of Lake Tana. A fully three-dimensional hydrodynamic model was combined with a watershed model and together, these models were successfully validated for the year 2006. The flow structure is characterized by large recirculation and secondary flow regions. Secondary flows are induced by hydrodynamic instabilities occurring at the interfaces of layers with a velocity gradient and the interaction with the irregularities of the bed. The weak stratification process in Lake Tana is characterized by a classic summer profile, which is more pronounced during January-February. Mixing processes in the lake are controlled by wind, the mixing energy induced by both river inflows and the lake outlet, and convective mixing due to the negative buoyancy. An alarming fall of the water levels in Lake Tana was found in response to the planned water withdrawal. The long flushing time (19 months) will not allow a fast decay of contaminated materials released into the lake. The flow structure will not be significantly modified by the planned water withdrawal but the flushing time will decrease. The hydrodynamics of Lake Tana resemble a closed system similar to a shallow reservoir with an overflow type outlet. The implication is that the lake is vulnerable to changes in external conditions and sustainable use of the water resource of the lake will require awareness of this vulnerability. The combined watershed and hydrodynamic models would be effective tools to achieve this awareness. It is also necessary to address the impact of climate change on the fate of the lake. These are all difficult challenges that need to be addressed to safeguard the sensitive eco-system of the area.

  • 16.
    Doolaeghe, D.
    et al.
    Univ Rennes, CNRS, Geosci Rennes, UMR 6118, 263 Ave Gen Leclerc, F-35042 Rennes, France..
    Darcel, C.
    Itasca Consultants SAS, 29 Ave Joannes Masset, F-69009 Lyon, France..
    Selroos, Jan-Olof
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Swedish Nucl Fuel & Waste Management Co SKB, Box 3091,Evenemangsgatan 13, S-16903 Solna, Sweden..
    Davy, P.
    Univ Rennes, CNRS, Geosci Rennes, UMR 6118, 263 Ave Gen Leclerc, F-35042 Rennes, France..
    Controls on fracture openness and reactivation in Forsmark, Sweden2023In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, no 1, article id 6686Article in journal (Refereed)
    Abstract [en]

    In crystalline bedrock, the open fraction of the fracture network constitutes the main pathways for fluids. Many observations point out that the state of stress influences the open fraction, likely indicating recent reactivation. But how this occurs is still unresolved. We analyse the conditions for fracture reactivation from fracture data collected in the uppermost 1 km of bedrock in Forsmark, Sweden. The open fraction is mainly correlated to the stress acting normally on the fracture but even away from critical failure, leading us to analyse the potential fluid pressure required for reactivation, P-c. We observe that 100% of the fractures are open when P-c is hydrostatic, and the ratio decreases exponentially to a plateau of similar to 17% when P-c is lithostatic and above. Exceptions are the oldest fractures, having a low open fraction independent of P-c. We suggest that these results reflect past pressure build-ups, potentially related to recent glaciations, and developing only if the preexisting open fraction is large enough.

  • 17.
    Estevez-Ventosa, Xian
    et al.
    Univ Vigo, Dept Nat Resources & Environm Engn, CINTECX, GESSMin Grp, Campus Lagoas, Vigo 36310, Pontevedra, Spain..
    Castro-Filgueira, Uxia
    Univ Vigo, Dept Nat Resources & Environm Engn, CINTECX, GESSMin Grp, Campus Lagoas, Vigo 36310, Pontevedra, Spain..
    Gonzalez-Fernandez, Manuel A.
    Univ Vigo, Dept Nat Resources & Environm Engn, CINTECX, GESSMin Grp, Campus Lagoas, Vigo 36310, Pontevedra, Spain..
    Garcia-Bastante, Fernando
    Univ Vigo, Dept Nat Resources & Environm Engn, CINTECX, GESSMin Grp, Campus Lagoas, Vigo 36310, Pontevedra, Spain..
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Swedish Nucl Fuel & Waste Management Co SKB, Evenemangsgatan 13,Box 3091, SE-16903 Stockholm, Sweden..
    Alejano, Leandro R.
    Univ Vigo, Dept Nat Resources & Environm Engn, CINTECX, GESSMin Grp, Campus Lagoas, Vigo 36310, Pontevedra, Spain..
    Scale effects on triaxial peak and residual strength of granite and preliminary PFC3D models2022In: Geomechanics and Engineering, ISSN 2005-307X, E-ISSN 2092-6219, Vol. 31, no 5, p. 461-476Article in journal (Refereed)
    Abstract [en]

    Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (Dmax and Dmin) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or phi v) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.

  • 18.
    Fernlund, Joanne M. Robison
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Tafesse, Solomon
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Magnusson, Mimmi K.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Total analysis of till using resistivity and 3D image analysisArticle in journal (Other academic)
  • 19.
    Fernlund, Joanne
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Tafesse, Solomon
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Magnusson, Mimmi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Lithological analysis of multiple size fractions of tillArticle in journal (Other academic)
  • 20.
    Fälth, Billy
    et al.
    Clay Technol AB, Lund, Sweden..
    Grigull, Susanne
    SKB Swedish Nucl Fuel & Waste Management Co, Solna, Sweden..
    Gåling, Jenny
    SKB Swedish Nucl Fuel & Waste Management Co, Solna, Sweden..
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. SKB Swedish Nucl Fuel & Waste Management Co, Solna, Sweden.
    Wagner, Frederic
    SKB Swedish Nucl Fuel & Waste Management Co, Solna, Sweden..
    Comment on "Modelling coseismic displacements of fracture systems in crystalline rock during large earthquakes: Implications for the safety of nuclear waste repositories" as published by Lei and Loew (2021) in IJRMMS, 138, 1045902022In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 150, article id 105013Article in journal (Refereed)
  • 21.
    Ghaderi, Abdolvahed
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Shahri, Abbas Abbaszadeh
    Islamic Azad Univ, Fac Civil Engn, Roudehen Branch, Tehran, Iran..
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    A visualized hybrid intelligent model to delineate Swedish fine-grained soil layers using clay sensitivity2022In: Catena (Cremlingen. Print), ISSN 0341-8162, E-ISSN 1872-6887, Vol. 214, p. 106289-, article id 106289Article in journal (Refereed)
    Abstract [en]

    In the current paper, a hybrid model was developed to generate 3D delineated soil horizons using clay sensitivity (St) with 1 m depth intervals in a landslide prone area in the southwest of Sweden. A hybridizing process was carried out using generalized feed forward neural network (GFFN) incorporated with genetic algorithm (GA). The model was conducted by means of seven variables consisting of the geographical coordinates and piezocone penetration test data (CPTu). The output of model (St) as a description of the effect of soil disturbance on shear strength plays a significant role in landslides in Sweden and thus can be applied for site-specific evaluation. Therefore, the use of St-based models to delineate soil layers can be a cost-effective solution to improve geoengineering design practices and assist in the reduction of related environmental risks, such as catastrophic landslide events or excavation failures. Evaluated model performance based on different applied soil classifications showed 4.38% improvement in the predictability level of GFFN-GA compared to optimum GFFN. Accordingly, delineated soil layers were evaluated using different criteria including previous landslides as well as supplementary geophysical and geotechnical investigations. The results show that the adopted hybrid GFFN-GA is an efficient tool that can potentially be applied to delineate soil horizons for the prediction of future events.

  • 22.
    Henkel, Herbert
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Piazolo, Sandra
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    A deep rock laboratory in the Dellen impact crater2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    The Deep Rock Lab is a platform to establish a comprehensive subsurface bedrock characterization approach, by integrating site characterization techniques applied from different disciplines of geo-mechanics, geochemistry, hydrogeology, structural geology, lithology and geophysics, with consideration of the effects of coupled geological processes of importance for the understanding of groundwater renewal, continental shield deformations, engineering issues related to geological disposal of nuclear waste and CO2, and geothermal energy retrieval in crystalline rocks. The approach will focus on the physics and chemistry of crystalline rocks and groundwater with down-the-hole measurements of relevant variables, using and developing more efficient geo-scientific site investigation techniques for deep boreholes at a chosen site, and develop more advanced down-the-hole measurements and numerical modelling methods with more advanced inversion algorithms to help integrate data interpretations and object representations. The goal is to develop this platform into a long-term research facility that can be readily used by the scientific community for both subsurface fundamental and engineering-oriented research. Such a platform will be especially important for the education of PhD students for generations to come. The integrated drilling and research facility is suggested to be located at the Dellen site. This site has an impact crater with a large range of expected physical property changes with depth, complex and multiple thermal processes that have affected the bedrock, a favorable infrastructure and local supporting activities, and a large body of existing geo-scientific data.

  • 23. Hollesen, J.
    et al.
    Elberling, B.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Modelling temperature-dependent heat production over decades in High Arctic coal waste rock piles2011In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 65, no 2, p. 258-268Article in journal (Refereed)
    Abstract [en]

    Subsurface heat production from oxidation of pyrite is an important process that may increase subsurface temperatures within coal waste rock piles and increase the release of acid mine drainage, AMD. Waste rock piles in the Arctic are especially vulnerable to changes in subsurface temperatures as the release of AMD normally is limited by permafrost. Here we show that temperatures within a 20 year old heat-producing waste rock pile in Svalbard (78 degrees N) can be modelled by the one-dimensional heat and water flow model (CoupModel) with a new temperature-dependent heat-production module that includes both biological and chemical oxidation processes and heat source depletion over time. Inputs to the model are meteorological measurements, physical properties of the waste rock material and measured subsurface heat-production rates. Measured mean annual subsurface temperatures within the waste rock pile are up to 10 C higher than the mean annual air temperature of -5.8 degrees C. Subsurface temperatures are currently decreasing with 0.5 degrees C per year due to decreasing heat production, which can be modelled using an exponential decay function corresponding to a half-life period of pyrite oxidation of 7 years. Simulations further suggest that subsurface temperatures two years after construction of the pile may have been up to 34.0 degrees C higher than in 2009 and that the release of AMD may have been more than 20 times higher. Sensitivity simulations show that maximum temperatures in the pile would have been up to 30.5-32.5 degrees C lower and that the pile would have been frozen 12-27 years earlier if the pile had been initially saturated with water, constructed with a thickness half of the original or a combination of both. Simulation show that the pile thickness and waste rock pyrite content are important factors controlling the internal build up of heat leading to potential self-incineration. However, site specific measurements of temperature-dependent heat production as well as simulation results show that the heat produced from pyrite oxidation alone cannot cause such a temperature increase and that processes such as heat production from coal oxidation may be equally important. (C) 2010 Elsevier B.V. All rights reserved.

  • 24.
    Hu, Yingtao
    et al.
    Zhejiang Univ, MOE Key Lab Soft Soils & Geoenvironm Engn, Hangzhou 310058, Peoples R China.;Zhejiang Univ, Ctr Hypergrav Expt & Interdisciplinary Res, Hangzhou 310058, Peoples R China..
    Xu, Wenjie
    Zhejiang Univ, MOE Key Lab Soft Soils & Geoenvironm Engn, Hangzhou 310058, Peoples R China.;Zhejiang Univ, Ctr Hypergrav Expt & Interdisciplinary Res, Hangzhou 310058, Peoples R China..
    Zhan, Liangtong
    Zhejiang Univ, MOE Key Lab Soft Soils & Geoenvironm Engn, Hangzhou 310058, Peoples R China.;Zhejiang Univ, Ctr Hypergrav Expt & Interdisciplinary Res, Hangzhou 310058, Peoples R China..
    Zou, Liangchao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Chen, Yunmin
    Zhejiang Univ, MOE Key Lab Soft Soils & Geoenvironm Engn, Hangzhou 310058, Peoples R China.;Zhejiang Univ, Ctr Hypergrav Expt & Interdisciplinary Res, Hangzhou 310058, Peoples R China..
    Modeling of solute transport in a fracture-matrix system with a three-dimensional discrete fracture network2022In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 605, article id 127333Article in journal (Refereed)
    Abstract [en]

    Understanding the fluid flow and solute transport mechanisms in fractured rocks is essential for many geo-engineering applications. In this study, the fluid flow and solute transport in a fracture-matrix system with a three-dimensional (3-D) discrete fracture network (DFN) are modelled through an efficient numerical simulation workflow. The simulation approach is used to systematically investigate the effects of the rock matrix on the transport behaviors in a fracture-matrix system. The results show that the mass exchange between the DFN and the rock matrix can be accurately evaluated based on the conforming mesh at the interface between the fractures (using triangular elements) and the rock matrix (using tetrahedral elements). The complementary cumulative distribution function curves (CCDFs) for the physical processes that consider sorption and decay exhibit significant long tail characteristics, which suggests that the sorption and decay processes play an important role in retarding the migration of solutes in fractured rocks. It is also found that a larger matrix porosity enhances the mass exchange at the interface between the DFN and the rock matrix, which consequently promotes the matrix diffusion effects. The distribution of the concentration plumes in the matrix demonstrates in fracture-matrix systems with larger fracture densities could result in a better connection between the fracture networks and the larger interface (specific wetting) areas, which therefore, promotes the mass exchange. These findings are critical to understanding the migration behavior of radioactive nuclides in far field areas and for the deep geological disposal of nuclear waste.

  • 25.
    Huber, Florian M.
    et al.
    Karlsruhe Inst Technol KIT, Inst Nucl Waste Disposal INE, POB 3640, D-76021 Karlsruhe, Germany..
    Leone, Debora
    Karlsruhe Inst Technol KIT, Inst Nucl Waste Disposal INE, POB 3640, D-76021 Karlsruhe, Germany..
    Trumm, Michael
    Karlsruhe Inst Technol KIT, Inst Nucl Waste Disposal INE, POB 3640, D-76021 Karlsruhe, Germany..
    Moreno, Luis
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering.
    Wenka, Achim
    Karlsruhe Inst Technol KIT, Inst Micro Proc Engn IMVT, Hermann Von Helmholtz Pl 1, DE-76344 Eggenstein Leopoldshafen, Germany..
    Schaefer, Thorsten
    Friedrich Schiller Univ Jena FSU, Inst Geosci, Appl Geol, Burgweg 11, D-07749 Jena, Germany..
    Impact of rock fracture geometry on geotechnical barrier integrity - A numerical study2021In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 142, article id 104742Article in journal (Refereed)
    Abstract [en]

    The effect of fracture geometry on bentonite erosion for a generic repository site in crystalline host rock environment was investigated by means of 2-d numerical simulations. Fracture geometry was varied systematically using random aperture normal distributions with a mean aperture of 1 mm and standard deviations between 0 and 0.7 mm, respectively. Moreover, two aperture correlation lengths (0.2 m and 2 m) were applied. Based on the synthetic fracture aperture fields generated the cubic law in conjunction with the Darcy equation is used to simulate fracture flow fields for mean flow velocities in the fracture between 1 x 10(-5) m/s and 1 x 10(-7) m/s. These flow fields are used in a two-way coupling approach to bentonite erosion simulations. The results of the study clearly show the influence of variable fracture aperture on bentonite erosion behaviour and erosion rates (kg/a). Increasing fracture aperture standard deviation leads to increasing heterogeneous flow velocity distributions governing the erosion behaviour and erosion rates. Calculated steady state erosion rates are in the range of similar to 0.25 kg/a down to similar to 0.014 kg/a. The highest erosion rate is calculated for the highest mean flow velocity in conjunction with the highest standard deviation. The effect of aperture heterogeneity diminishes for the lowest flow velocities. In summary, the results show the effect of fracture heterogeneity on bentonite erosion, especially for high to medium mean flow velocities combined with high to medium fracture heterogeneity under the model boundary conditions and model capabilities and limitations considered. An increase of up to g heterogeneous flow velocity distributions governing the erosion behaviour and erosion rates. Calculated steady state erosion rates are in the range of similar to 83% in erosion rate compared to the constant aperture case highlights the need to consider fracture aperture heterogeneity and its effect on the bentonite erosion in the assessment of the safety and evolution of a high-level nuclear waste repository.

  • 26. Jacobsson, L.
    et al.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. SKB, Swedish Nuclear Fuel and Waste Management Company, Stockholm, Sweden..
    Kasani, H. A.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Lam, T.
    Experimental program on mechanical properties of large rock fractures2021In: IOP Conference Series: Earth and Environmental Science, IOP Publishing , 2021, Vol. 833, no 1, p. 012015-Conference paper (Refereed)
    Abstract [en]

    Predictions of fracture displacements are required to support the safety assessments of a deep geological repository for nuclear spent fuel. Laboratory and in-situ experiments are used to estimate these properties. Despite significant contributions in the last decades, there is a knowledge gap in terms of the impact of high normal stresses on the mechanical properties of large-scale fractures under Constant Normal Stiffness (CNS) boundary conditions. Within the framework of the POST project, a cooperative effort was made by SKB (Sweden), NWMO (Canada), and Posiva from Finland (in phase 1) to study these questions. In the second phase of the POST project, a first of a kind direct shear testing machine was manufactured and calibrated that can accommodate samples up to 400 × 600 mm under normal stresses up to 10 MPa, for both CNS and Constant Normal Load (CNL) conditions, with the ability to shear the sample up to 50 mm. Several best practice procedures were developed for fracture characterization pre-, syn-, and post-shear test which utilize high resolution optical scanning, contact pressure measurements, Digital Image Correlation (DIC) measurements, and acoustic emission measurements during the shear test. Natural and tensile-induced fractures of a granitic rock as well as replicas of the hard rock fractures, at three different fracture sizes of 35×60 mm, 70×100 mm, and 300×500 mm, are now being tested. It is hoped that this program will provide a set of high-quality data which will help reduce the knowledge gap in the understanding of fracture behavior.

  • 27.
    Jin, Yunzhe
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    He, Chen
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Yao, Chi
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Sun, Zhejie
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Zhang, Xiaobo
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Yang, Jianhua
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Jiang, Qinghui
    State Key Laboratory of Civil Engineering, Wuhan University, Wuhan, 430072, China.
    Zhou, Chuangbing
    School of Infrastructure Engineering, Nanchang University, Nanchang, 330032, China.
    Effects of in-situ stress on heat transfer in fracture networks2024In: Geomechanics for Energy and the Environment, ISSN 2352-3808, Vol. 37, article id 100516Article in journal (Refereed)
    Abstract [en]

    Stress-induced fracture deformation is the principal cause for permeability change in geothermal systems. This study focuses on the influence of the nonlinear deformation and dilation effect of fractures on the geothermal system under the action of in-situ stress. By adopting a nonlinear constitutive model of rock fractures and embedding discrete fracture networks, numerical studies are first conducted to investigate the effects of different in-situ stress schemes on fracture aperture evolution using a rigid-body spring method. Based on the anisotropic aperture field of the fracture network caused by the in-situ stress, a finite element method is then used to study the flow and heat transfer process. The effects of different stress schemes on the heat flow transfer process are analyzed. Numerical simulation results show that when the ratio of horizontal to vertical stresses is not sufficient to cause shear dilation effects, the nonlinear normal deformation is the main factor affecting flow and heat transfer. In this case, the heat extraction efficiency is reduced. As the stress ratio increases, the shear dilation gradually becomes the dominant mechanism, and the heat extraction performance is improved. The obtained results provide a practical guide for geothermal site siting and optimizing heat extraction efficiency in geothermal reservoirs.

  • 28.
    Jing, Lanru
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Feng, X
    Main rock mechanics issues in geological disposal of radioactive wastes: Yanshilixue Yu Gongcheng Xuebao2006In: Chinese Journal of Rock Mechanics and Engineering, ISSN 1000-6915, Vol. 25, no 4, p. 833-841Article in journal (Refereed)
    Abstract [en]

    Geological disposal of radioactive wastes is a multi-disciplinary issue of importance for national interest. It stimulated many challenging scientific and technical issues, and at a higher level, presented a series of demanding requirements for a country's overall research and development programme, its implementation and engineering practice, about basic policies and legislature concerning nuclear energy, defense, waste management and environment. Rock mechanics and rock engineering are very important fields for geological disposal of radioactive wastes, and contribute significantly to the conceptual design, site investigation, engineering design and construction, operation and the long-term safety assessment of the waste repositories. It plays, therefore, a irreplaceable role in the research and development programme of geological disposal of radioactive wastes. In this paper, we first summarizes briefly the main steps about repository system, followed by the major demands for rock mechanics and rock engineering during feasibility study and site investigation, and the major international trends concerning these issues. The focus is placed on the coupled thermo-hydro-mechanical and chemical (THMC) processes and the current status of research in international communities. At the end, the progresses in research and development works in the field of radioactive waste disposal in China are presented; and possible future working directions are discussed.

  • 29. Jing, Lanru
    et al.
    Stephansson, Ove
    Fundamentals of Discrete Element Methods for Rock Engineering2007Book (Refereed)
  • 30. Jing, Lanru
    et al.
    Stephansson, Ove
    Research results from the DECOVALEX III BECHPAR Projects2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 591-870Article in journal (Refereed)
  • 31.
    Johansson, Teddy
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Artificial Ground Freezingin Clayey Soils: Laboratory and Field Studies of Deformations During Thawing at the Bothnia Line2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Artificial ground freezing as a method to temporarily stabilize and create hydraulic sealing in urban as well as in rural areas has been used in a number of Swedish construction projects, particularly during the last decade.

    One problem with the freezing of soil and rock is that fine-grained clayey types of soils have showed a tendency to under certain circumstances, during the thawing process, create a pore water overpressure and to consolidate, despite a change in the external loading conditions. In certain cases, this condition can be a desired effect as the soil mass after a freeze- and thaw cycle acquires overconsolidated properties.

    The main objectives of this study are, to describe and review the knowledge and current state of practice of artificial ground freezing, to increase the understanding about the conceptual behaviour for prognosis of the vertical deformation concerning artificial ground freezing and to compare and discuss results from laboratory and field studies concerning vertical deformation during thawing process for Bothnia soil.

    The field studies and the laboratory tests in this research study have been performed with soil from the freezing of the Bothnia Line in the vicinity of Stranneberget. The Bothnia Line is the railway link between Nyland, north of Kramfors, and Umeå.

    This thesis relates to a part of the Bothnia Line. It deals with the behaviour of soil during thawing by means of temporary stabilization and hydraulic sealing of fine-grained soil through artificial freezing using brine as the cooling agent. However, the reason behind the problem consists of the final deformations due to the thawing process.

    The general conclusions of this study are;

    • the Bothnia soil water content decreased in mean approximately 14 % after a freeze-thaw cycle, which approximately corresponds to; wth = 0.8w – 1.5
    • the decrease of the water content has no correlation to the depth below ground surface, in contrast, there is a strong correlation between the undisturbed soil water content and the magnitude of the decrease in water content
    • the soil liquid limit decreases after a freeze-thaw cycle, simultaneously as the relative share of clay and fine silt grains decreases while the relative share of more coarse grains increases
    • the coarser and denser soil created after a freeze-thaw cycle obtains an increased preconsolidation pressure and an increased undrained shear strength.
    Download full text (pdf)
    Teddy Johansson Dr Thesis 20090914 (14MB)
    Download (pdf)
    Teddy Johansson SPIKBLAD 20090914
  • 32.
    Kamarad, Anthony
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Design and construction of a mobile equipment for thermal response test in borehole heat exchangers2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In 2010, the Ground Source Heat Pumps (GSHPs) market in the European Union went up over one million (1 014 436 units at the end of 2010 according to EUROBSERV’ER 2011). In 2011, it was estimated around 1.25 million according to Bayer et al. (2012). With more than 378 000 units installed in 2010, according to the Swedish heat pump association (SVEP), the Swedish GSHPs market was the first in the EU. As for the French GSHPs market, it was estimated to 151 938 units in service in 2010, which propelled France at the third rank in the EU. However, despite a relatively important number of GSHPs installed in the whole EU, since 2008 GSHP sales have shrank. Even Sweden which has been the most competitive country sees its GSHP sales decline in the first quarter of 2012 (EUROBSERV’ER 2011).

    This report is the achievement of my Master of Science Thesis project. It also represents the end of my studies at INSA Lyon in France and concludes my degree in Energetic and Environment Engineering. This report deals with the improvement of a heat injection apparatus which is available at KTH (Royal Institute of Technology). This equipment is better known as Thermal Response Test (TRT) apparatus. This kind of equipment improves Borehole Heat Exchangers (BHE) design in terms of size and cost benefits. This technology is generally used to design GSHP installations in both domestic and industrial purposes. It allows to determine really important thermal BHE parameters: the thermal conductivity of the ground and the borehole thermal resistance. The report covers a theoretical description of TRT experiments, the reasons and objectives of such a project, the apparatus design and its construction. The last part is dedicated to a first experimental laboratory results and some problems met during the project course. 

    Download full text (pdf)
    Kamarad Anthony EGI-2012-054MSC
  • 33.
    Kizito, Frank
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Management and Assessment.
    Ngirane-Katashaya, Gaddi
    Thunvik, Roger
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Management and Assessment.
    Using geovisualisation to support participatory problem structuring and decision making for an urban water utility in Uganda2008In: Applied GIS, E-ISSN 1832-5505, Vol. 4, no 2, p. 1-33Article in journal (Refereed)
    Abstract [en]

    This paper describes the application of geovisualisation to facilitate participatory identification and structuring of problems in an urban water supply system in Uganda. The city of Kampala has experienced rapid expansion over the years, with a corresponding increase inthe demand for piped water supply. However, this demand was not well matched with expansion of the water supply system, and as a result parts of the city have been facingchronic supply anomalies and insufficiencies. Faced with the task of identifying remedies to theproblems in the system, the city water company undertook a formal participatory problemstructuring and decision analysis process, to try and understand the underlying causes of system failures as well as the geospatial patterns of these failures. As part of this process,analysis, mapping and geovisualisation of data derived from historical records of waterconsumption, as well as records of pipe breakages, supply intermittences, and other recordedcustomer complaints, was done. The maps so produced were key in bringing the variousstakeholders and decision makers to a common understanding of the problem issues, andhelped in the formulation of alternative courses of action. Furthermore, with the establishment of a formal discussion forum for problem analysis and decision making, structured participatory decision making was entrenched within the company’s work ethos. It is hoped that in future,the coupling of the geovisualisation tools with the existing operational databases in thecompany will result in the development of a functional spatial decision support system and adynamic framework for system performance monitoring and reliability assessment.

  • 34.
    Kolesnikov, Anton
    et al.
    Carnegie Inst Washington, Geophys Lab.
    Kutcherov, Vladimir G.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Goncharov, Alexander F.
    Methane-derived hydrocarbons produced under upper-mantle conditions2009In: Nature geosicence, ISSN 1752-0894, Vol. 2, no 8, p. 566-570Article in journal (Refereed)
    Abstract [en]

    There is widespread evidence that petroleum originates from biological processes(1-3). Whether hydrocarbons can also be produced from abiogenic precursor molecules under the high-pressure, high-temperature conditions characteristic of the upper mantle remains an open question. It has been proposed that hydrocarbons generated in the upper mantle could be transported through deep faults to shallower regions in the Earth's crust, and contribute to petroleum reserves(4,5). Here we use in situ Raman spectroscopy in laser-heated diamond anvil cells to monitor the chemical reactivity of methane and ethane under upper-mantle conditions. We show that when methane is exposed to pressures higher than 2 GPa, and to temperatures in the range of 1,000-1,500 K, it partially reacts to form saturated hydrocarbons containing 2-4 carbons (ethane, propane and butane) and molecular hydrogen and graphite. Conversely, exposure of ethane to similar conditions results in the production of methane, suggesting that the synthesis of saturated hydrocarbons is reversible. Our results support the suggestion that hydrocarbons heavier than methane can be produced by abiogenic processes in the upper mantle.

  • 35.
    Koyama, Tomofumi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Numerical modelling of fluid flow and particle transport in rough rock fracture during shear2005Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The effects of different shearing processes and sample sizes on the fluid flow anisotropy and its impact on particle transport process in rough rock fractures are significant factors that need to be considered in the performance and safety assessments of underground nuclear waste repositories. The subjects, however, have not been adequately investigated previously in either laboratory experiments or numerical modeling. This thesis addresses these problems using numerical modeling approaches.

    The modeling consists of two parts: 1) fluid flow simulations considering more complex but realistic flow boundary conditions during shear processes that cannot be realized readily in laboratory experiments, using digitalized fracture surfaces scanned in the laboratory, so that anisotropic fluid flow induced by shearing with channeling phenomenon can be directly simulated and quantified; 2) particle tracking simulations to demonstrate the impacts of such channeling effects on characteristic properties of particle transport. The numerical method chosen for the simulations is the Finite Element Method (FEM). Scale effects were considered in the simulations by using fracture surface samples of different sizes.

    The distributions of fracture aperture during shear were obtained by numerically generating relative translational and rotary movements between two digitalized surfaces of a rock fracture replica without considering normal loading. From the evolutions of the aperture distributions during the shearing processes, the evolutions of the transmissivity fields were determined by assuming the validity of the cubic law locally. A geostatistical approach was used to quantify the scale effects of the aperture and transmissivity fields. The fluid flow was simulated using different flow boundary conditions, corresponding to translational and rotary shear processes. Corresponding to translational shear (with a 1 mm shear displacement interval up to a maximum shear displacement of 20 mm), three different flow patterns, i.e., unidirectional (flow parallel with and perpendicular to the shear direction), bi-directional and radial, were taken into account. Corresponding to rotary shear (with a 0.5o shear angle interval up to 90o), only the radial flow pattern was considered. The particle transport was simulated using the Particle Tracking Method, with the particles motion following the fluid velocity fields during shear, as calculated by FEM. For the unidirectional particle transport, the breakthrough curves were analyzed by fitting to an analytical solution of 1-D advection-dispersion equation. The dispersivity, Péclet number and tracer velocity, as well as their evolutions during shear, were determined numerically.

    The results show that the fracture aperture increases anisotropically during translational shear, with a more pronounced increase in the direction perpendicular to the shear displacement, causing significant fluid flow channelling. A more significant increase of flow rate and decrease in travel time of the particles in the direction perpendicular to the shear direction is predicted. The particle travel time and characteristics are, correspondingly, much different when such effects caused by shear are included. This finding may have an important impact on the interpretation of the results of coupled hydro-mechanical and tracer experiments for measurements of hydraulic properties of rock fractures, because hydraulic properties are usually calculated from flow test results along the shear directions, with the effects of the significant anisotropic flow perpendicular to the shear direction ignored. The results also show that safety assessment of a nuclear repository, without considering the effects of stress/deformation of rocks on fluid flow and transport processes, may have significant risk potential. The results obtained from numerical simulations show that fluid flow through a single rough fracture changes with increasing sample size, indicating that representativehydro-mechanical properties of the fractures in the field can only be accurately determined using samples of representative sizes beyond their stationarity thresholds.

    Download full text (pdf)
    FULLTEXT01
  • 36.
    Koyama, Tomofumi
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Stress, Flow and Particle Transport in Rock Fractures2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The fluid flow and tracer transport in a single rock fracture during shear processes has been an important issue in rock mechanics and is investigated in this thesis using Finite Element Method (FEM) and streamline particle tracking method, considering evolutions of aperture and transmissivity with shear displacement histories under different normal stresses, based on laboratory tests.

    The distributions of fracture aperture and its evolution during shear were calculated from the initial aperture fields, based on the laser-scanned surface roughness features of replicas of rock fracture specimens, and shear dilations measured during the coupled shear-flow-tracer tests in laboratory performed using a newly developed testing apparatus in Nagasaki University, Nagasaki, Japan. Three rock fractures of granite with different roughness characteristics were used as parent samples from which nine plaster replicas were made and coupled shear-flow tests was performed under three normal loading conditions (two levels of constant normal loading (CNL) and one constant normal stiffness (CNS) conditions). In order to visualize the tracer transport, transparent acrylic upper parts and plaster lower parts of the fracture specimens were manufactured from an artificially created tensile fracture of sandstone and the coupled shear-flow tests with fluid visualization was performed using a dye tracer injected from upstream and a CCD camera to record the dye movement. A special algorithm for treating the contact areas as zero-aperture elements was used to produce more accurate flow field simulations by using FEM, which is important for continued simulations of particle transport, but was often not properly treated in literature. The simulation results agreed well with the flow rate data obtained from the laboratory tests, showing that complex histories of fracture aperture and tortuous flow channels with changing normal stresses and increasing shear displacements, which were also captured by the coupled shear-flow tests of fracture specimens with visualization of the fluid flow. From the obtained flow velocity fields, the particle transport was predicted by the streamline particle tracking method with calculated flow velocity fields (vectors) from the flow simulations, obtaining results such as flow velocity profiles, total flow rates, particle travel time, breakthrough curves and the Péclet number, Pe, respectively.

    The fluid flow in the vertical 2-D cross-sections of a rock fracture was also simulated by solving both Navier-Stokes (NS) and Reynolds equations, and the particle transport was predicted by streamline particle tracking method. The results obtained using NS and Reynolds equations were compared to illustrate the degree of the validity of the Reynolds equation for general applications in practice since the later is mush more computationally efficient for large scale problems. The flow simulation results show that the total flow rate and the flow velocity predicted by NS equations are quite different from that as predicted by the Reynolds equation. The results show that a roughly 5-10 % overestimation on the flow rate is produced when the Reynolds equation is used, and the ideal parabolic velocity profiles defined by the local cubic law, when Reynolds equation is used, is no longer valid, especially when the roughness feature of the fracture surfaces changes with shear. These deviations of flow rate and flow velocity profiles across the fracture aperture have a significant impact on the particle transport behavior and the associated properties, such as the travel time and Péclet number. The deviations increase with increasing flow velocity and become more significant when fracture aperture geometry changes with shear.

    The scientific findings from these studies provided new insights to the physical behavior of fluid flow and mass transport in rock fractures which is the scientific basis for many rock mechanics problems at the fundamental level, and with special importance to rock engineering problems such as geothermal energy extraction (where flow rate in fractures dominates the productivity of a geothermal energy reservoir) and nuclear waste repositories (where radioactive nuclides transport through fractures dominates the final safety evaluations) in fractured rocks.

    Download full text (pdf)
    FULLTEXT01
  • 37.
    Koyama, Tomofumi
    et al.
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    Fardin, Nader
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    Shear-induced anisotropy and heterogeneity of fluid flow in a single rock fracture with translational and rotary shear displacements: a numerical study2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 3, p. 426-426Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Fardin, Nader
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Stephansson, Ove
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Numerical simulation of shear-induced flow anisotropy and scale-dependent aperture and transmissivity evolution of rock fracture replicas2006In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 43, no 1, p. 89-106Article in journal (Refereed)
    Abstract [en]

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

  • 39.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Effects of shearing processes on the fluid flow and particle transport in a single rock fracture2006In: Rock mechanics in underground construction: ISRM International Symposium 2006 / [ed] Leung, CF Y, Zhou, YX, 2006, p. 408-Conference paper (Refereed)
  • 40.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Li, B.
    Jiang, Y.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Numerical simulations for the effects of normal loading on particle transport in rock fractures during shear2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 8, p. 1403-1419Article in journal (Refereed)
    Abstract [en]

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

  • 41.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Vilarrasa, Victor
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Tracer transport in a rough rock fracture during shear: a numerical study2006In: Proc of the 2nd International Conference on Coupled T-H-M-C Processes in Geo-Systems: Fundamentals, 2006, p. 575-580Conference paper (Refereed)
    Abstract [en]

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

  • 42.
    Koyama, Tomofumi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Vilarrasa, Victor
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Shear-induced flow channels and its effect on the particle transport in a single rock fractureIn: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157Article in journal (Other academic)
    Abstract [en]

    The effect of mechanical shearing on fluid flow anisotropy and particle transport in rough rock fractures was investigated using numerical modeling. Two opposite surfaces of a rock fracture of 194x194 mm in size were laser scanned to generate their respective digital profiles. Fluid flow through the fracture was simulated using a finite element code that solves the Reynolds equation, while incremental relative movement of the upper surface was maintained numerically to simulate a shearing process without normal loading. The motion of solute particles during shearing was studied using a simple particle-tracking code. It was found that shearing introduces anisotropy in both fluid transmissivity and particle motion, with a greatly increased flow rate and particle travel velocity in the direction perpendicular to the direction of shear. This finding has an important impact in the interpretation of the results of coupled hydro-mechanical and tracer transport experiments of hydraulic and transport properies of rock fractures.

  • 43. Li, B.
    et al.
    Mo, Y.
    Zou, Liangchao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Liu, R.
    Cvetkovic, V.
    Influence of surface roughness on fluid flow and solute transport through 3D crossed rock fractures2020In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 582, article id 124284Article in journal (Refereed)
    Abstract [en]

    The influence of surface roughness on fluid flow and solute transport through three-dimensional (3D) crossed rock fractures are investigated by numerical simulations. Three crossed fracture models with different degrees of surface roughness are established by two intersecting rough-walled fractures with four branches. The fracture surface morphological data are measured from three natural fractures in sandstone and granite rock samples. The fluid flow is simulated by solving the Navier-Stokes equations and solute transport is simulated by solving the advective-diffusion equation. By rotating one fracture plane while fixing the other, series of intersection models with different angles between the two crossed fractures are established to investigate the influence of the intersecting angle. Simulation results of the rough-walled fractures are compared with the smooth parallel-plate model, showing that the surface roughness significantly enhances channeling and mixing for fluid flow and solute transport at fracture intersections. The mechanism is that the complex geometry of the intersection for rough-walled models results in reallocation of fluid pathways at the intersection, which consequently affect the mixing behavior depending on the Peclet number. The intersecting angle affects the channeling and mixing behavior because it influences the geometrical structure of the fracture intersection. The correlation between the mixing ratio and the geometrical characteristics of intersections is quantified by a relative roughness parameter. The results reveal that the widely adopted smooth parallel-plate model may lead to significant uncertainty in predicting the solute transport in crossed fractures, especially at intersections with unmated fracture surfaces. The correlation between the mixing ratio and the roughness parameter developed in this study can be incorporated into discrete fracture network models to improve their performance in estimating solute transport in fractured rocks.

  • 44. Li, B.
    et al.
    Wang, Y.
    Zou, Liangchao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Yang, L.
    Displacement laws of grout-water two-phase flow in a rough-walled rock fracture through visualization tests2022In: Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering, ISSN 1000-4548, Vol. 44, no 9, p. 1608-1616Article in journal (Refereed)
    Abstract [en]

    The grouting in water-rich fractured rock masses is a process in which the pressurized grouts gradually displace the existing water. It is important to thoroughly investigate the grout-water displacement laws for improving the engineering grouting efficiency. In this study, a visualization technique that incorporates the particle image velocimetry (PIV) into the grout-water displacement tests is established, and is used to capture the flow field distribution in a 3D-printed transparent rough-walled fracture along with the flow velocity and hydraulic pressure measurements. The Navier-Stokes equations are solved based on the finite element method to simulate the displacement process, and the simulation is compared with the experimental observations. The results show that under the constant flow rate, the injection pressure first increases gently, followed by a rapid increase stage, and finally approaches a constant value. The grouts preferentially flow through some major channels, and the injection pressure tends to increase gently after the grout reaches the outlet. The residual water is mainly distributed in the dead end close to the edge of main flow channels and the locations where sudden changes in aperture happen. The parallel-plate model can underestimate the injection pressure by up to 45% comparing to the corresponding rough-walled model. It is therefore necessary to consider fracture roughness in the theoretical assessment of grouting pressures to achieve better grouting performance. 

  • 45. Li, B.
    et al.
    Ye, P. -J
    Huang, L.
    Wang, D.
    Zhao, C.
    Zou, Liang-Chao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.
    Deformation and acoustic emission characteristics of dry and saturated rock fractures2021In: Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering, ISSN 1000-4548, Vol. 43, no 12, p. 2249-2257Article in journal (Refereed)
    Abstract [en]

    The natural rock masses are situated in various complex geological conditions. Quantitative description of the deformation and failure behaviors of rock fractures under these conditions is of fundamental importance for the studies related to their mechanical behaviors. In this study, the unconfined compression tests and the elastic-plastic contact numerical simulations are implemented to study the compressive deformation and failure behavior of two kinds of rock fractures under dry and saturated conditions, together with acoustic emission detection and analysis. The results show that the normal stress-displacement curves and the plastic failure areas obtained from the experiment and the numerical simulation agree well with each other, which verifies the reliability of the contact method. The mean increment of plastic deformation decreases nonlinearly with the increasing normal stress with a decreasing rate, and a fitting formula is established using mechanical and geometric parameters. The position of acoustic emission (AE) sources matches with the damage area obtained from the experiment and the numerical simulation. Both the AE ringing count and the cumulative count are higher in dry rocks than those in saturated rocks. The AE ringing count and the mean increment of plastic deformation follow an identical changing trend. These results reveal the controlling role played by the fundamental mechanical parameters and geometric properties in the deformation and failure behaviors of rock fractures. 

  • 46.
    Li, Bo
    et al.
    Tongji Univ, Dept Geotech Engn, Shanghai, Peoples R China.;Shaoxing Univ, Key Lab Rock Mech & Geohazards Zhejiang Prov, Shaoxing, Peoples R China..
    Cui, Xiaofeng
    Shaoxing Univ, Key Lab Rock Mech & Geohazards Zhejiang Prov, Shaoxing, Peoples R China..
    Zou, Liangchao
    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.
    On the Relationship Between Normal Stiffness and Permeability of Rock Fractures2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 20, article id e2021GL095593Article in journal (Refereed)
    Abstract [en]

    The hydraulic permeability and normal stiffness of rock fractures are fundamentally related, which can serve as a probe for assessing hydro-mechanical properties in a variety of geo-engineering contexts. We present experimentally validated numerical simulations of fracture closure and fluid flow processes in realistic aperture structures with mean in the range of 0.01-2 mm. A relatively simple relationship between permeability and normal stiffness is derived in the effective medium regime, using the elastic modulus of the rock matrix, the mean mechanical aperture, and the relative standard deviation (RSD) of the local mechanical aperture. The established relationship between stiffness and permeability appears independent of scale or orientation. Plain Language Summary A natural rock fracture is formed by two rough walls that create complex internal void space structures. Subject to an increasing normal stress, the bridging asperities jointing a fracture deform elastically at first, and then may fail when the local stress reaches critical strength. These elastic and elastic-plastic mechanisms determine the closure behavior of a fracture and the evolution of void spaces that provide the paths for fluid flow. In such a manner, the deformability of a fracture (stiffness) is fundamentally related to the permeability that is controlled by the average aperture of void spaces and their spatial distributions. We prepared a series of natural and synthetic rock fractures with apertures falling in the typical engineering range. By conducting experimental and numerical investigations on the normal loading and fluid flow processes, we were able to obtain a relatively simple relationship between the permeability and normal stiffness in the effective flow regime. This relationship is composed of broadly accepted physical parameters and is independent of scale or direction. It can help the estimation of fracture stiffness from the permeability or fracture permeability from stiffness, depending on which quantity is observable in the field. Key Points Laboratory tests and numerical simulations are combined to analyze the relationship between normal stiffness and permeability in rock fractures Effects of surface roughness, matedness and fracture scale on normal stiffness and permeability are investigated A physically based stiffness-permeability relationship is established for rock fractures in the effective medium regime

  • 47.
    Li, Bo
    et al.
    Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China.
    Xu, Jiujun
    Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing University, Shaoxing 312000, China.
    Zhong, Jie
    Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing University, Shaoxing 312000, China.
    Huang, Na
    College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao 266590, China.
    Zou, Liangchao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.
    Effects of surface roughness and shear processes on solute transport through 3D crossed rock fractures2023In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 170, article id 105529Article in journal (Refereed)
    Abstract [en]

    The influences of surface roughness and shear processes on fluid flow and solute transport through three-dimensional (3D) crossed rock fractures, a vital element of fracture networks, were systematically investigated. Surfaces of tensile fractures created by splitting granite and sandstone samples along its two orthogonal central axes were optically scanned to generate rough-walled crossed fracture models. Shearing processes on the models were realized by assigning experimentally measured normal and shear displacements to one fracture while fixing the other. Fluid flow and solute transport through the models were numerically simulated taking into account different combinations of inlets and outlets, in which distilled water and solution are injected into the two inlets, respectively. The results show that compared to the parallel-plate model, the rough-walled crossed fracture model exhibits obvious flow channelization and fluid redistribution at the intersection, significantly promoting the mixing. The shear process affects the mixing at the intersection as it induces dilation and geometric change of the intersection. Increasing shear displacement can either enhance or reduce the mixing depending on combinations of the inlets and outlets, and the mixing ratio is controlled by the aperture difference between two outlet branches and the surface roughness. Effects of surface roughness, shear displacement and shear-induced dilation on the mixing ratio are quantified, upscaling of which can be potentially useful for field-scale characterization of solute transport in fractured systems.

  • 48.
    Liu, Chia-Chuan
    et al.
    Natl Cheng Kung Univ, Tainan, Taiwan.
    Maity, Jyoti Prakash
    Natl Cheng Kung Univ, Tainan, Taiwan.
    Jean, Jiin-Shuh
    Natl Cheng Kung Univ, Tainan, Taiwan.
    Reza, A. H. M. Selim
    Natl Cheng Kung Univ, Tainan, Taiwan.
    Li, Zhaohui
    Univ Wisconsin Parkside, Kenosha, WI USA.
    Nath, Bibhash
    Univ Sydney, Sydney, NSW Australia .
    Lee, Ming-Kuo
    Auburn Univ, Auburn, AL USA.
    Lin, Kao-Hung
    Natl Cheng Kung Univ, Tainan, Taiwan.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Geochemical characteristics of the mud volcano fluids in southwestern Taiwan and their possible linkage to elevated arsenic concentration in Chianan plain groundwater2012In: ENVIRONMENTAL EARTH SCIENCES, ISSN 1866-6280, Vol. 66, no 5, p. 1513-1523Article in journal (Refereed)
    Abstract [en]

    Fluid and mud samples were collected from Wushanting (WST), Hsiaokunshui (HKS), Yenshuikeng (YSK), Kuantzeling (KZL), and Kunshuiping (KSP) mud volcanoes of southwestern Taiwan. Concentrations of major ions and trace elements in mud volcanic fluids were analyzed to find the possible linkage to elevated arsenic (As) concentrations in the Chianan plain groundwater. The elevated Na+, K+, and Cl- concentrations indicated possible marine origin of the fluids. The trace element concentrations in the mud volcanic fluids were generally low, but the As concentrations were up to 0.12 mg/L. High contents of As, Fe, and Mn were observed in the mud samples. Saturation index calculations indicated that both carbonate and oxide minerals acted as potential sinks for As in the mud volcanic fluids. Arsenic in the dewatering fluids and muds may be transported by the subsurface flow and surface streams as suspended solids and eventually deposited in the Chianan plain aquifers. Under reducing conditions, As may be released from the host minerals (such as Fe- and Mn-oxides/hydroxides), thereby causing widespread groundwater As pollution.

  • 49.
    Malmström, Maria
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Docampo Cabaleiro, Eva
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Regenspurg, Simona
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Modelling Ni(II) Sorption in Granitic Groundwater2006In: Geochimica et Cosmochimica Acta 70 (18):Suppl 1:A387., 2006, p. A387-A387Conference paper (Other academic)
  • 50. Marklund, Lars
    et al.
    Simic, Eva
    Wörman, Anders
    Swedish University of Agricultural Sciences.
    The impact of different geological parameters on transport of radionuclides2006In: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM, American Nuclear Society , 2006, p. 369-373Conference paper (Refereed)
    Abstract [en]

    Quaternary deposits and topography are two geological parameters which have a great impact on transport and retardation of radionuclides from a leaking repository of high level nuclear waste in crystalline bedrock. Due to the hydraulic and sorption properties of quaternary deposits, even thin layers significantly increase the residence time of leaking radionuclides. This study also shows that the flow paths predominantly discharge in low areas of the catchments where the layers of quaternary deposits often are relatively deep. The effect of topography is depending on the relationship between the local(kilometres) topography at the repository site and the large scale(hundreds of kilometres) topography surrounding the site area. The areas studied here, are located at discharge areas of deep groundwater flow, driven by large scale topography. Therefore residence times of radionuclides significantly decrease when large scale topography is accounted for. The impact of large scale topography is particularly clear in areas of flatter local topography.

123 1 - 50 of 116
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf