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  • 51.
    Krounis Guerrero, Alexandra
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Effects of spatial variation in cohesion over the concrete-rock interface on dam sliding stability2015In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 7, no 6, p. 659-667Article in journal (Refereed)
    Abstract [en]

    The limit equilibrium method (LEM) is widely used for sliding stability evaluation of concrete gravity dams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously. However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stress over the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. In addition, the spatial variation in cohesion may introduce weak spots where failure can be initiated. Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shear strength of the interface has not been studied previously. In this paper, numerical analyses are used to investigate the effect of brittle failure in combination with spatial variation in cohesion that is taken into account by random fields with different correlation lengths. The study concludes that a possible existence of weak spots along the interface has to be considered since it significantly reduces the overall shear strength of the interface, and implications for doing so are discussed.

  • 52.
    Larsson, Stefan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Wersäll, Carl
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Geotekniker och bergmekaniker ska lära för livet: men hur ska det gå till?2014In: Bygg & teknik, ISSN 0281-658X, no 1, p. 70-72Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Geoteknikeroch bergmekaniker ska ha förmågan att projektera, bygga och underhålla geokonstruktionerför det moderna samhället. Konstruktionerna måste vara både ekonomiska, säkra,estetiska och miljövänliga. Ingenjören får sin kompetens genom utbildning,träning och erfarenheter från skolan, annan fortbildning och arbete iprojekten. Kraven på en bred kunskapsbas ökar alltmer, samtidigt som det krävsen betydande fördjupning inom det specifika ämnesområdet. Både högskolorna ochnäringslivet genomgår nu ett påtagligt generationsskifte och det är därförlämpligt att inom de närmaste åren utföra en omfattande didaktisk analysavseende: Vad ska läras ut? Varför ska det läras ut? Hur ska det läras ut? Förvem ska det läras ut? Vi anser att geoteknik­ och bergmekanikundervisningen börinriktas på att ge ingenjören förmågor som ska utgöra en bas för ett livslångtlärande.

  • 53.
    Lazzari, Elisa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ivars, D. M.
    Juncal, A. S.
    Advances, current limitations and future requirements for a numerical shear box for rock joints using PFC2D2014In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium / [ed] R . Alejano , Áurea Perucho , Claudio Olalla , and Rafael Jiménez, Taylor & Francis Group, 2014, p. 763-768Conference paper (Refereed)
    Abstract [en]

    Rock mechanical problems are often governed by the shear strength of joints, but assessing it theoretically is difficult because of the many underlying factors. Consequently, expensive and time-consuming shear tests must be performed either in laboratory or in situ. Artificial shear tests based on numerical models would therefore be a valuable complement. In this paper, results from an initial study on real shear tests are compared with numerically simulated shear tests performed with the computer software PFC2D. The results from the analyses are good from a qualitative view, but also revealed the need for further research. In this paper, the results from the performed analyses are presented and the current limitations and requirements of further development are discussed.

  • 54. Lindfors, Ulf
    et al.
    Lope Alvarez, Diego
    Johansson, Fredrik
    Sweco Civil AB.
    Stille, Björn
    Spänningsmodellering av storskaliga strukturer i Stockholmområdet2017In: / [ed] Eva Friedman, 2017Conference paper (Other academic)
    Abstract [en]

    The expansion of the new metro in Stockholm includes several extensions and a new line. The expansion and the new line in the south will pass through a number of regional large-scale structures. The magnitude and orientation of the stresses close to structures are uncertain and stress measurements are not practically possible to conduct. To increase the understanding of the rock stress situation in the southern side of Stockholm  and to quantify stress conditions near the structures, a stress analysis in regional scale along the planned extension was conducted. The analysis was performed using threedimensional numerical modeling, where topography and known structures were included. The model included eleven minor structures assumed to be vertical and two major structures dipping 70°. The results showed that stress re-distributions occurs for a distance up to 50 m from the structures where, for example, higher or lower stress magnitudes are to be expected depending on the side of the faults.

  • 55.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Lastförutsättningar avseende istryck2017Report (Other academic)
  • 56.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Fransson, Lennart
    Luleå Tekniska Universitet.
    Alternative methods to determine the ice load on concrete dams2015Conference paper (Other academic)
  • 57.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ríos Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Load Capacity of Grouted Rock Bolts Due to Degradation: 2017:3742017Report (Other academic)
    Abstract [en]

    In this report, the influence of degradation on the strength of rock bolts has been studied. A literature study has been performed in order to determine the degradation rate and to present observations and conclusions from available assessments of rock bolts. All cases found in the literature have shown that the rock bolts on concrete dams are in good condition with only minor superficial corrosion even after 50 years of service. In the project, a methodology to account for the degradation mechanism in evaluations of dam safety is presented, where all possible failure modes of rock bolts are considered. The contribution of the rock bolts to the dam stability is based on the failure mode with the lowest strength. The degradation has been taken into account based on a German DIN standard based on the chemical content of the water. Most available field tests have only measured the load capacity of bolts, where the deformation is typically not recorded. The relationship between forces and deformations is however important input to verify numerical and analytical analyses. Therefore, field tests have been performed on rock bolts that been in service for 50 years. A previously developed test rig had been modified in this project to register both load and deflection of the pull-out test. The test rig consists of a hydraulic jack that presses a cylinder towards the rock surrounding the bolt. Due to this configuration of the test equipment, a rock cone failure cannot be captured. The results showed that the test rig may influence the obtained load capacity if the failure occurs in the grout. A case study is presented where analytical, probabilistic and finite element analyses were performed to assess the dam safety. Based on the numerical analyses, it was possible to study the development of forces in the rock bolts due to successively increasing loads. The numerical analyses showed (as expected) that the rock bolts are subjected to both shear and tensile forces at the same time. In addition, the shear force was constantly higher than the tensile forces and that the shear forces were about 10% of the total shear resistance for normal loads. This implies that it is important to use a failure criterion for the rock bolts that considers combinations of tensile and shear forces. Besides this, the probabilistic analyses showed that pure overturning failure is extremely unlikely and cannot be considered as a relevant failure mode. The numerical analyses showed that the deformation start as for overturning failure resulting in that parts of the contact surface (on the upstream side) lose its contact. Thereby, the shear forces have to be transmitted over a reduced area which initiates the sliding failure. This implies that it is more suitable to define a criterion that limits the tensile forces in the upstream toe from serviceability loads, rather than having an overturning failure criterion.

  • 58.
    Nejad Ghafar, Ali
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Sadrizadeh, Sasan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Draganović, Almir
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Lawrence Berkeley National Laboratory.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Application of Low-Frequency Rectangular Pressure Impulse in Rock Grouting2017In: Grouting 2017: Grouting, Drilling, and Verification / [ed] Byle, MJ Johnsen, LF Bruce, DA ElMohtar, CS Gazzarrini, P Richards, TD, American Society of Civil Engineers (ASCE), 2017, Vol. 2, no 288, p. 104-113Conference paper (Refereed)
    Abstract [en]

    In order to sufficiently seal an underground facility in fractured rock, it is essential to obtain adequate grout spread into the surrounding fractures. The grout spread itself depends on parameters, the most significant of which are the filtration tendency and rheological properties. These properties can be affected by the applied pressure. High-frequency oscillating pressure has been shown to improve grout spread by virtue of reducing the grout viscosity. However, this method has not yet been industrialized due to the quick dissipation of the oscillation along a fracture. In a recent investigation, we examined a low-frequency rectangular pressure-impulse using a short slot. The results showed significant improvements in the injected grout volume in comparison to the static pressure results. In this paper, we examine the method in a considerably longer artificial fracture in order to investigate the dissipation of the pressure impulses. The study indicates the potential of the method to improve the grout spread in rock grouting.

  • 59.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ligier, Pierre-Louis
    Lier, Öyvind
    Betongdammars brottförlopp2015Report (Other academic)
  • 60.
    Prästings, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Müller, Rasmus
    Tyréns AB.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Bjureland, William
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Implementing the Extended Multivariate Approach in Design with Partial Factors for a Retaining Wall in Clay2017In: ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering, ISSN 2376-7642, Vol. 3, no 4, article id 04017015Article in journal (Refereed)
    Abstract [en]

    Limitations with the current design using partial factors in Eurocode 7 have been identified. Uncertainties in the material properties are incorporated in both the cautious estimate of the characteristic value and the partial factor. Furthermore, the partial factor is fixed, which limits the opportunities to update the design when additional information is available. A more rational procedure of managing uncertainties in design with partial factors is proposed based on the Bayesian methodology referred to as the extended multivariate approach. The benefits of the approach are illustrated with a case study in which uncertainties of undrained shear strength are characterized for a Swedish clay. The characteristic value and design value is calculated in accordance with the Swedish national annex to Eurocode 7 by adjusting the otherwise fixed partial factor with a conversion factor allowable through EN 1990. The study highlights major benefits in managing uncertainties in a quantifiable and rational way.

  • 61. Rafi, J. Y.
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stiiie, Håkan
    Choice of pumping pressure in pre-grouting in scandinavian tunneling projects2016In: ITA-AITES World Tunnel Congress 2016, WTC 2016, Society for Mining, Metallurgy and Exploration , 2016, p. 124-134Conference paper (Refereed)
  • 62.
    Ríos Bayona, Francisco
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Bolin, Axel
    Swedish Transport Administration.
    Sánchez Juncal, Abel
    A&P Consultants.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Mas Ivars, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. SKB, Swedish Nuclear Fuel and Waste Management Co.
    Comparison between shear strength of real and numerical shear tests on rock joints using PFC2DManuscript (preprint) (Other academic)
  • 63.
    Ríos Bayona, Francisco
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Mas Ivars, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. SKB, Swedish Nuclear Fuel and Waste Management Co.
    Peak shear strength of natural and unfilled rock joints based on measured average apertureManuscript (preprint) (Other academic)
  • 64.
    Ríos Bayona, Francisco
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stigsson, Martin
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure. SKB, Swedish Nuclear Fuel and Waste Management Co.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Mas Ivars, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. SKB, Swedish Nuclear Fuel and Waste Management Co.
    Comparison between shear strength based on Barton’s roughness profiles and equivalent synthetic profiles based on fractal theory2018In: 52nd U.S. Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association (ARMA) , 2018Conference paper (Refereed)
    Abstract [en]

    A comprehensive understanding of the shear strength and the mechanical behavior of rock joints is to some extent still missing today. Several attempts have been made to develop empirical and analytical shear strength criteria that explain this mechanism. One of the most important parameters governing the shear strength of rock fractures is the surface roughness, which is generally determined using the Joint Roughness Coefficient (JRC). This parameter is often determined subjectively in the field by comparison with 10 predefined roughness profiles. Recent studies indicate that surface roughness can be accurately represented by using fractal analysis. The aim of this study is to perform a first attempt to investigate the mechanical equivalence in terms of the peak shear strength between synthetic rock fractures, where the surface roughness has been generated using fractal theory, and standard roughness profiles from Barton and Choubey, 1977, using the particle flow code PFC2D. The results from the numerical shear tests under constant normal load (CNL) are compared with the predicted peak shear strength using Barton’s criterion and a back-calculation of the JRC value is carried out.

  • 65.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Damasceno, Davi
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Jan
    Naturgasteknik AB.
    Stojanovic, Bojan
    Vattenfall.
    Simonsson, Nicklas
    Vattenfall.
    Storskalig lagring av vätgas i bergrum2019In: Bygg och Teknik, ISSN 0281-658X, no 1, p. 41-44Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Sveriges stålproduktion släpper idag ut stora mängder växthusgaser. Med initiativet HYBRIT hoppas SSAB, LKAB och Vattenfall göra stålproduktionen fossilfri genom att använda vätgas i processen. I HYBRIT:s forskningsprogram RP1 bidrar KTH Jord- och bergmekanik med att utveckla och förfina storskalig teknik för lagring av vätgas i bergrum. Artikeln beskriver de viktigaste frågeställningarna i forskningsprojektet.

  • 66.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    When is the observational method in geotechnical engineering favourable?2017In: Structural Safety, ISSN 0167-4730, E-ISSN 1879-3355, Vol. 66, p. 17-26Article in journal (Refereed)
    Abstract [en]

    The observational method in geotechnical engineering is an acceptable verification method for limit states in Eurocode 7, but the method is rarely used despite its potential savings. Some reasons may be its unclear safety definition and the lack of guidelines on how to establish whether the observational method is more favourable than conventional design. In this paper, we challenge these issues by introducing a reliability con­straint on the observational method and propose a probabilistic optimi­sation methodology that aids the decision-making engineer in choosing between the observational method and conventional design. The method­ology suggests an optimal design after comparing the expected utilities of the considered design options. The methodology is illustrated with a practical example, in which a geotechnical engineer evaluates whether the observational method may be favourable in the design of a rock pillar. We conclude that the methodology may prove to be a valuable tool for deci­sion-making engineers’ everyday work with managing risks in geotech­nical projects.

  • 67.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Observationsmetoden – hur svårt kan det vara?2015Conference paper (Other academic)
  • 68.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    On the use of pore pressure measurements in safety reassessments of concrete dams founded on rock2013In: Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, ISSN 1749-9518, E-ISSN 1749-9526, Vol. 8, no 2, p. 117-128Article in journal (Refereed)
    Abstract [en]

    In probabilistic stability analyses of concrete dams founded on rock, the uplift pressure is often a parameter of major importance. In previous literature, it has been suggested that assessing uplift with pore pressure measurements, instead of using empirical assumptions, could improve the calculated dam safety. This paper presents a coherent methodology to investigate whether incorporating pore pressure measurements has any impact on the calculated dam safety, based on Bayesian linear regression of pore pressure data in combination with series-system and the first-order reliability method. The study concludes that the probability of sliding failure is closely related to the probability of an extreme increase in uplift. Hence, measured uplift should only be incorporated while this probability remains sufficiently small, which requires proper programs both for uplift monitoring and for maintenance of drains and grout curtains.

  • 69.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Reducing uplift pressure uncertainty with measurements under concrete dams2013In: Proceedings ICOLD 2013 International Symposium, Denver: US Society on Dams , 2013, p. 2551-2560Conference paper (Refereed)
    Abstract [en]

    In quantitative risk analyses of concrete dams founded on rock, it is necessary to consider the uplift pressure in the foundation with respect to both mean value and variation. With a more accurately predicted uplift pressure, the calculated probability of failure of the dam can be reduced. This paper proposes a methodology for predicting the current uplift pressure and related uncertainty, based both on pore pressure measurements and on expert judgment. An illustrative example is presented and the suggested methodology is compared with other conceivable approaches. The results are found to be reasonable in most conditions. However, it should be recognized that in risk analyses of dams, more extreme load cases not captured by the measurements also must be considered.

  • 70.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Tillståndsbedömning av betongdammar grundlagda på berg med observationsmetoden2013In: Bygg & teknik, ISSN 0281-658X, no 1, p. 83-87Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Observationsmetoden erbjuder ett alternativ till dagens mer etablerade dimensioneringsmetoder för geokonstruktioner. På Avdelningen för jord- och bergmekanik på Kungliga Tekniska högskolan (KTH) pågår för tillfället ett forskningsprojekt om när och i vilka typer av projekt som denna metod kan vara lämplig att använda, då man bygger i och på berg. Nu påbörjar vi ett delprojekt som syftar till att undersöka om och hur observationsmetoden kan tillämpas vid tillståndsbedömning av betongdammar grundlagda på berg, som ett led i att utveckla förvaltningen av Sveriges bestånd av dammar. Projektet finansieras av Svenskt Vattenkraftcentrum (SVC), Stiftelsen Bergteknisk forskning (BeFo) och Formas.

  • 71.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Towards an improved observational method2014In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium, Taylor & Francis Group, 2014, p. 1435-1440Conference paper (Refereed)
    Abstract [en]

    The observational method is today an accepted method in Eurocode 7 for design of geotechnical structures. However, case studies with formal application of its principles are still rare. One reason could be that the method to some extent is considered complex and associated with low safety margins. In fact, the Eurocode does not give any reference to how the safety of the completed structure can be assured. This paper strives to open up a discussion on how the observational method can be improved by including a requirement for a safety margin of the completed structure. A methodology is outlined and illustrated with a simple calculation example analysing the safety of a square rock pillar. Lastly, the compatibility with the observational method is discussed.

  • 72.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Uotinen, Lauri K.T.
    Department of Civil and Environmental Engineering, Aalto University.
    Rafi, Jalaleddin
    BGC engineering Inc.
    Using observational method to manage safety aspects of remedial grouting of concrete dam foundations2016In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529, Vol. 34, no 5, p. 1613-1630Article in journal (Refereed)
    Abstract [en]

    As concrete dams age, the need for remedial grouting to reduce the seepage and uplift pressure in the rock foundations under them increases. Based on a case study of a Swedish dam with very low calculated safety against sliding, this paper discusses the application of the observational method (as defined in Eurocode 7) to manage safety aspects during remedial grouting. The studied case was complex in that grouting works posed the risk of causing increased uplift pressure, which could have induced sliding failure along a shallow, persistent, horizontal rock joint in the foundation. The approach applied in the studied case mainly followed the principles of the observational method, except in some highly significant safety aspects for which alternative procedures are suggested and discussed. Implementing these procedures along with the observational method offers a coherent framework to manage the safety aspects of the remedial grouting of concrete dam foundations that is in line with modern risk-informed dam safety policies.

  • 73.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Palmström, Arild
    Rock Mass AS.
    Hur ska bergbyggande kunna inkluderas i Eurokod 7: How to include rock engineering in Eurocode 72019In: Proceedings Bergdagarna 2019, 2019Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Sweden, among other countries, has chosen not to apply Eurocode 7 to rock engineer­ing design. However, Eurocode 7 is currently under revision, with one purpose being to improve its applicability to rock engineering. Such a revision would however require that the code accommodates the current principles of rock engineering design and exe­cution, since rock engineering in many cases fundamentally differs from other types of construction. In this presentation, we give our view on how a design code for rock engineering needs to be organized, in order to ensure that new rock engineering struc­tures become both sufficiently safe and cost-effectively constructed. An important pre­requisite is having a decision-theoretical connection between design and risk manage­ment that always should permeate geotechnical design and construction. The presented research is based on the results from a research project funded by the Rock Engineering Research Foundation (BeFo) that was finalized in January 2019.

  • 74.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Palmström, Arild
    RockMass Consulting Co, Ovre Smestad Vei 35E, N-0378 Oslo, Norway..
    On the Need for a Risk-Based Framework in Eurocode 7 to Facilitate Design of Underground Openings in Rock2018In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 51, no 8, p. 2427-2431Article in journal (Refereed)
    Abstract [en]

    The European design code for geotechnical engineering, EN-1997 Eurocode 7, is currently under revision. As design of underground openings in rock fundamentally differs from design of most other types of structures, the revised Eurocode 7 must be carefully formulated to be applicable to underground openings. This paper presents the authors' view of how a design code for underground openings in rock needs to be organized to ensure that new structures are both sufficiently safe and constructed cost-effectively. The authors find that the revised version of Eurocode 7 carefully must acknowledge the fundamental decision-theoretical connection between design and risk management that should permeate all geotechnical design work. Otherwise, if the revised code is not given a risk-based framework, the authors fear that, as a consequence, the observational method will not be favorable to use in excavations of underground openings in rock. Then, cost-effective construction will be very difficult to achieve.

  • 75.
    Stigsson, Martin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Some aspects on the applicability of peak shear strength criteriaManuscript (preprint) (Other academic)
  • 76.
    Stille, B.
    et al.
    Department of Civil Infrastructure, AECOM Nordic AB, Stockholm, Sweden.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Department of Civil Infrastructure, AECOM Nordic AB, Stockholm, Sweden.
    Ríos Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Department of Civil Infrastructure, AECOM Nordic AB, Stockholm, Sweden.
    Batres Estrada, R.
    Department of Civil Infrastructure, AECOM Nordic AB, Stockholm, Sweden.
    Roslin, M.
    Swedish Transport Administration, Stockholm, Sweden.
    Stockholm bypass project – passage under the Lake Mälaren2019In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress (WTC 2019), May 3-9, 2019, Naples, Italy / [ed] Daniele Peila, Giulia Viggiani, Tarcisio Celestino, London: CRC Press, 2019, p. 1569-1578Conference paper (Refereed)
    Abstract [en]

    In the last years, the Swedish Transport Administration has been working on improving and expanding road communications in Sweden. The Stockholm Bypass Project, one of the biggest projects in Swedish history, consists of a 21 km long highway that goes around the city from north to south. In order to reduce the environmental impact, 17 km of the total length will be excavated underground passing through several regional fault zones and subsea passages. One of the most difficult technical challenges in this project is the passage under the Lake Mälaren and the regional fault zone in the Fiskar fjord. This paper presents the utilized methodology to design the temporary rock support and to manage the risks and uncertainties for the excavation through the fault zone, which mainly originate from the limited information about the rock conditions and the relatively large width of the tunnels.

  • 77. Swindell, Robert
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Kjellström, Ingrid
    ÅF Consult.
    Benhalimi, Mehdi
    Karaktärisering av bergmassor – systematiska fel och möjliga åtgärder2017In: / [ed] Eva Friedman, 2017Conference paper (Other academic)
    Abstract [en]

    Rock mass quality assessment is performed in a variety of situations by engineers andgeologists during design and excavation of rock engineering projects. The results form thebasis for rock engineering design and are an important part of the tender documents andcontract for rock engineering works. Trafikverket sponsored two Masters Theses to analyzethe occurrence and possible causes of systematic “errors” introduced during rock masscharacterization. This paper provides a summary of the results of these theses and shows thatthere are clear indications that systematic “errors” are introduced due to the methods used forrock mass characterization. The paper also provides suggestions for how these errors can bemitigated in future projects. Possible remedial measures include the introduction of guidelinesfor drill core logging, incorporation of geotechnical baseline reports, better coupling of rockmass characterization and rock engineering design, implementation of guidelines forexcavation mapping and continued statistical analysis of rock mass characterization data.

  • 78. Uotinen, L. K. T.
    et al.
    Korpi, E.
    Hartikainen, A.
    Yorke, R.
    Antikainen, J.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE).
    Rinne, M.
    A method to downscale joint surface roughness and to create replica series using 3D printed molds2017In: 13th ISRM International Congress of Rock Mechanics, International Society for Rock Mechanics , 2017Conference paper (Refereed)
    Abstract [en]

    In order to determine the in-situ shear strength of rock joints, large scale testing is required. However, this is both expensive and difficult to execute. One possible method to overcome this may be to use photogrammetry to capture large joint surface roughness in-situ and downscale it to replica samples, which could be sheared in laboratory. In this paper, as a first part in such a method, a technique to digitize surface roughness and to produce replica samples for laboratory shear testing from a larger joint sample are presented. First, a thin granitic rock slice with dimensions of 1.75 m x 0.95 m of granitic intact rock was chosen for the study. The joint surface is fresh and created through tensile induced splitting. The large joint sample is digitized using photogrammetry. Then, one fullscale 1.7 m x 0.6 m geometry is cropped from the digitized joint geometry and then subsamples at 10x, 7.5x, 5x, 2.5x and 1x scales. All sub-geometries are scaled down digitally to produce 0.17 m by 0.06 m geometries. The geometries are used to make casting molds both positive and negative to produce samples with perfect matedness. The casting molds are 3D printed in polylactic acid plastic and C60/75 concrete is cast to produce a replica series. In addition to the creation of this replica series, two pilot replicas are also tested using a portable shear box with a 0.5 MPa normal pressure. The results from the pilot rounds are presented and discussed. Finally, suggestions for future research are given.

  • 79.
    Vestberg Wilde, Marie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Suggested probabilistic model code for probability-based assessment of concrete dams2015In: ICOLD 25th Congress/ICOLD 83rd Annual Meeting/Symposium Hydropower 15, 2015Conference paper (Other academic)
    Abstract [en]

    For design and assessment of concrete dams the standard procedure is to calculate safety factors and compare with some experience-based requirements. Probability-based design and assessment is still in its infancy, but in recent years an increasing number of papers has been presented in different contexts, e.g. ICOLD (2009), 3IWRDD (2011). This paper describes the background and main contents of a suggested “probabilistic model code for concrete dams” that gives recommendations on how to perform probabilistic analysis of concrete gravity and buttress structures. The purpose of the work is to educate dam owners, consultants and researchers in Sweden and to, in the long-term, implement probability-based guidelines and, if found appropriate, partial factors. In this paper, some of the most important points in the PMCD are described and an example is given on the use. The main conclusion from the work is that the code enables probabilistic analyses and also comparisons of dams. When several dams are analyzed using similar assumptions, for their specific context, the resulting comparison will become a useful tool to identify the necessary remedial works.

  • 80.
    Westberg, Mari
    et al.
    Lund University.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Possible consequences of deterministic design of concrete dams: a comparison to probabilistic design2010In: Dam Safety: Sustainability in a Changing Environment, 2010Conference paper (Refereed)
  • 81. Westberg, Mari
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    System for concrete dam reliability with respect to foundation stability2012In: Proceedings of the 3rd International Forum on Risk Analysis, Dam Safety Dam Security and Critical Infrastructure Management, 3IWRDD-FORUM, CRC Press, 2012, p. 87-92Conference paper (Refereed)
    Abstract [en]

    In order to perform a complete risk analysis of a dam facility, it is necessary to have information about the probability and consequences of failure. To analyze the probability of failure of a concrete dam, all components and all failure modes must be accounted for. This paper presents a methodology for the calculation of the failure probability of a concrete dam with respect to foundation stability where the dam is considered as a system. The system is divided into different levels, where the top event on the "structure level" is failure of the dam. The next level is "monolith level", where each monolith can be considered as an element in a series system of the concrete dam. Below the monolith level is the "failure location level" which describes where the failure occurs, in the concrete-rock contact, in the rock mass or in the concrete. Since it is the weakest of these failure locations that will govern where the failure occurs, each failure location can be seen as elements in a series system. Beneath this level is the "failure mode level" where failure modes such as sliding and rotation also constitute elements in a series system. The "Basic failure modes" are the foundation level in the system. In some situations, the reliability of all failure modes as well as the correlation between failure modes is of importance for the overall reliability. In other situations only the reliability of a dominant failure mode is of importance. A discussion regarding this is given.

  • 82.
    Westberg Wilde, Marie
    et al.
    ÅF Industry, Stockholm, Sweden .
    Johansson, Fred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Probability-based guidelines for design and assessment of concrete dams2013In: Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures - Proceedings of the 11th International Conference on Structural Safety and Reliability, ICOSSAR 2013 / [ed] George Deodatis, Brude R. Ellingwood, Dan M. Frangopol, London: Taylor & Francis Group, 2013, p. 5187-5194Conference paper (Refereed)
    Abstract [en]

    Dams are designed and assessed based on a factor of safety methodology. Several drawbacks of this approach exist; for example varying failure probability for structures where the factor of safety is the same. Dam owners in Sweden recently decided to bring forth a probability-based guideline. This paper describes the intended process, where the first step is to put together a probabilistic model code for concrete dams based on JCSS Probabilistic model code (2001). A summary of the level of knowledge for relevant limit states, safety index and load and resistance parameters, as well as the expected difficulties involved in the process are also discussed.

  • 83.
    Westberg Wilde, Marie
    et al.
    ÅF Industry.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE).
    Analysis of concrete dams based on "Probabilistic model code for concrete dams"2015Conference paper (Refereed)
  • 84.
    Westberg Wilde, Marie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. ÅF.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Sweco.
    Probablilistic model code for concrete dams.: Report 2016:2922016Report (Other academic)
    Abstract [en]

    The Probabilistic model code for concrete dams presented in this document is a first attempt to put together in a consistent way rules, regulations and explanations necessary for design and assessment of concrete dams from a probabilistic point of view. It is believed that this document will be helpful to perform probabilistic assessments of concrete dams in a systematic way.

    The Probabilistic Model Code for Concrete dams is divided into three parts: Part I: Basis of design, Part II: Load models and Part III: Resistance models. The document also contains one example of a probabilistic assessment.

    Basis of design is based on JCSS (2001), Eurocode 1990 (2001) and ISO 2394 , with some changes has been in order to be applicable for concrete dams and dam safety. Basis of design contains general principles, information of how a probabilistic verification is performed; limit states and design situations, limit state functions and target reliabilities relevant for concrete dams. It also contains a part on updating of prior estimates. The target reliabilities applied are similar to those described in e.g. SS-EN 1990, but are based on calibration of the existing practice. This is further described in Westberg Wilde & Johansson (2016).

    In Part II Load models general descriptions on loads and load modelling are given, based on JCSS (2001). Next relevant loads for concrete dams are discussed and “best estimates” on statistical descriptions are presented. Part II includes ice loads, hydrostatic pressure, uplift and earth pressure.

    In Part III Resistance models general descriptions on resistance and resistance modelling is given, based on JCSS (2001). Next relevant resistance parameters for concrete dams are discussed and “best estimates” on statistical descriptions are presented. The resistance parameters included are self weight, friction properties of concrete/rock contact and in rock, material properties (concrete, rock, steel), rock bolts and rock anchors.

    Finally an example is given. In the example a probabilistic analysis of a concrete gravity dam is performed, based on the Probabilistic model code.

    The process of bringing forth this document and the calibration procedure is further described in Westberg Wilde & Johansson (2016).

  • 85.
    Westberg Wilde, Marie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. ÅF.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rios Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Altarejos Garcia, Luis
    Theme D - Syntheis: Risk analysis – assessment of reliability for concrete dams: 14th International Benchmark Workshop on Numerical Analysis of Dams2018Report (Refereed)
    Abstract [en]

    In the last decade the attention and application of a reliability-based methodology for concrete dams has increased. A recent project aiming at bringing forth a reliability-based methodology for design and assessment of concrete dams founded on rock for conditions applicable in a Nordic climate has resulted in a “Probabilistic model code for concrete dams” (PMCD). The objective of Theme D was to estimate probability of failure of an existing concrete dam for sliding along the concrete/rock interface and sliding along a joint in the rock mass, using the PMCD. The dam analyzed is a 25 m high concrete gravity dam located in the north part of Sweden. Contributions from six authors were received and have been analysed in this summary along with a reference solution by the authors. The first assignment was to estimate the deterministic factor of safety. Although the definitions of the factor of safety were similar there was large differences in the results. For the probabilistic analysis, definition of limit state functions was straight forward and have been defined similarly. Variables in the probabilistic analysis were defined somewhat differently, e.g. for concrete density, friction angle and ice loads. The results of the probabilistic analysis of sliding along the interface for normal water levels were varying, although five of the results were within the range of β = 3.7-5. There was less variability for the flood load case and for sliding along the rock joint. There reason was considered to be mainly due to the different parameter definitions. Identification of the most important parameters was successful; although the exact sensitivity values varied (due to variation in parameters), the most important factors were identified. In the calculation of system reliability, the previously described differences were reflected. Bayesian updating proved to be a tricky task, where especially results of the updated standard deviation varied. One conclusion is, however, that the updating of the friction angle is rewarding in terms of increasing the safety index due to the reduction in epistemic uncertainties.

    For a probabilistic methodology to be trustworthy it should produce stable and reproducible results. The conclusion is that the PMCD is successful as a guideline in this process, but that further development and more experience of practical use is necessary. More benchmarks of similar characteristics are thus believed to be a good way forward and a broader discussion among practitioners would also be beneficial in reaching a “consensus” on how to perform reliability-based assessments.

  • 86. Wilde, Marie Westberg
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    System Reliability of Concrete Dams with Respect to Foundation Stability: Application to a Spillway2013In: Journal of Geotechnical and Geoenvironmental Engineering, ISSN 1090-0241, E-ISSN 1943-5606, Vol. 139, no 2, p. 308-319Article in journal (Refereed)
    Abstract [en]

    Structural reliability analysis is not widely used for the design and assessment of concrete dams. In this paper, the system reliability of a spillway structure consisting of two monoliths is calculated. Limit state functions are defined from the failure modes sliding in the concrete rock contact, sliding in the rock mass, and adjusted overturning. Random variables in the limit state functions are defined by stochastic distributions. These are defined based on site investigations and laboratory tests from samples taken at the dam. Simulations and information from the literature are used for the remaining variables. The safety index is calculated by the first-order reliability method for each failure mode and monolith, and the system reliability is approximated by direct integration of the bivariate normal distribution. The output is the safety index including associated sensitivity values at the single failure mode, monolith, and system levels. The results show that the system safety is governed by a persistent rock joint beneath one monolith. A system reliability analysis is found to be a useful tool in the dam risk management process as it can be used to calculate the probability of failure and to identify important failure modes and variables.

  • 87.
    Zhou, Pin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    A comparison between the represenatative volume for circular excavations and rectangular rock mass samplesIn: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Other academic)
  • 88.
    Zhou, Pin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    On the use of the continuity factor for rock mass properties based on a literature review of the representative elementary volume2014In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium, Taylor & Francis Group, 2014, p. 427-431Conference paper (Refereed)
    Abstract [en]

    The REV (Representative Elementary Volume) is widely employed to define the scale limit when the continuum or discontinuum method is suitable for rock mass analyses. A simplified tool is needed as an aid to approximate this limit. The Continuity Factor (CF) was proposed by Palmstrom for this purpose. The definition of the CF implies that the joint spacing is the most significant parameter for the REV. However, other parameters might also influence the REV. In this paper, a literature review of derived REVs is performed. For each REV, the average block size is calculated. The correlation between the REV and the average block size index I-b is thereafter analyzed. The results show that a CF limit of approximately four may exist for the geometrical and the mechanical REV. If other parameters exists that significantly influence the REV are discussed.

  • 89.
    Zhou, Pin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Numerical study on the continuity factor and the limits between continuous and discontinuous behaviors2012In: ISRM International Symposium 28-30 May 2012, Stockholm, 2012Conference paper (Refereed)
    Abstract [en]

     Discontinuum approach or equivalent continuum approach is usually adopted in order to model the behavior of rock masses. The latter approach is more frequently used. However, this approach might be unacceptable for slightly-jointed rock masses. The continuity factor (CF), mainly derived from empirical experience, is defined as the ratio of the tunnel span to the block diameter. It is commonly used to determine whether a rock mass should be modeled as a continuum or a discontinuum material. Only a few analyses regarding the CF have been performed previously. In order to study the limits between continuous and discontinuous behavior, nu-merical analyses with UDEC have been performed. In these analyse, a rock mass with two sets of orthogonal joints are initially generated. From this rock mass, square areas corresponding to a certain CF are randomly chosen as models in UDEC. Confined compression test is conducted on the mentioned model and the constrained modulus (Dm) regarding this rock mass is calculated. Due to the variations of the relative loca-tions between the square and the joints cut inside, as well as the joint quantity and the joint lengths, several Dm are yielded for each CF. Several CFs are also analyzed and the results are compared with previous suggested limits between continuous and dis-continuous behaviors.

12 51 - 89 of 89
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