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  • 1.
    Abbaszadeh Shahri, Abbas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. College of Civil Engineering, Roudehen branch, Islamic Azad University, Tehran, Iran.
    Larsson, Stefan
    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.
    CPT-SPT correlations using artificial neural network approach: A Case Study in Sweden2015In: Electronic Journal of Geotechnical Engineering, E-ISSN 1089-3032, Vol. 20, no 28, p. 13439-13460Article in journal (Refereed)
    Abstract [en]

    The correlation between Standard and Cone Penetration Tests (SPT and CPT) as two of the most used in-situ geotechnical tests is of practical interest in engineering designs. In this paper, new SPT-CPT correlations for southwest of Sweden are proposed and developed using an artificial neural networks (ANNs) approach. The influences of soil type, depth, cone tip resistance, sleeve friction, friction ratio and porewater pressure on obtained correlations has been taken into account in optimized ANN models to represent more comprehensive and accurate correlation functions. Moreover, the effect of particle mean grain size and fine content were investigated and discussed using graph analyses. The validation of ANN based correlations were tested using several statistical criteria and then compared to existing correlations in literature to quantify the uncertainty of the correlations. Using the sensitivity analyses, the most and least effective factors on CPT-SPT predictions were recognized and discussed. The results indicate the ability of ANN as an attractive alternative method regarding to conventional statistical analyses to develop CPT-SPT relations.

  • 2.
    Abbaszadeh Shahri, Abbas
    et al.
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Updated relations for the uniaxial compressive strength of marlstones based on P-wave velocity and point load index test2016In: INNOVATIVE INFRASTRUCTURE SOLUTIONS, ISSN 2364-4176, Vol. 1, no 1, article id UNSP 17Article in journal (Refereed)
    Abstract [en]

    Although there are many proposed relations for different rock types to predict the uniaxial compressive strength (UCS) as a function of P-wave velocity (V-P) and point load index (Is), only a few of them are focused on marlstones. However, these studies have limitations in applicability since they are mainly based on local studies. In this paper, an attempt is therefore made to present updated relations for two previous proposed correlations for marlstones in Iran. The modification process is executed through multivariate regression analysis techniques using a provided comprehensive database for marlstones in Iran, including UCS, V-P and Is from publications and validated relevant sources comprising 119 datasets. The accuracy, appropriateness and applicability of the obtained modifications were tested by means of different statistical criteria and graph analyses. The conducted comparison between updated and previous proposed relations highlighted better applicability in the prediction of UCS using the updated correlations introduced in this study. However, the derived updated predictive models are dependent on rock types and test conditions, as they are in this study.

  • 3.
    Abbaszadeh Shahri, Abbas
    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.
    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.
    Kartering av skredbenägenhet medartificiell intelligens2018In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, no 1Article in journal (Other academic)
  • 4.
    Abbaszadeh Shahri, Abbas
    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.
    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.
    Landslide susceptibility hazard map in southwest Sweden using artificial neural network2019In: Catena (Cremlingen. Print), ISSN 0341-8162, E-ISSN 1872-6887, Vol. 183, article id UNSP 104225Article in journal (Refereed)
    Abstract [en]

    Landslides as major geo-hazards in Sweden adversely impact on nearby environments and socio-economics. In this paper, a landslide susceptibility map using a proposed subdivision approach for a large area in southwest Sweden has been produced. The map has been generated by means of an artificial neural network (ANN) model developed using fourteen causative factors extracted from topographic and geomorphologic, geological, land use, hydrology and hydrogeology characteristics. The landslide inventory map includes 242 events identified from different validated resources and interpreted aerial photographs. The weights of the causative factors employed were analyzed and verified using accepted mathematical criteria, sensitivity analysis, previous studies, and actual landslides. The high accuracy achieved using the ANN model demonstrates a consistent criterion for future landslide susceptibility zonation. Comparisons with earlier susceptibility assessments in the area show the model to be a cost-effective and potentially vital tool for urban planners in developing cities and municipalities.

  • 5.
    Abbaszadeh Shahri, Abbas
    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.
    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.
    Storskalig kartering av skredbenägenhet i västra Götaland med artificiell intelligens2018Conference paper (Other academic)
  • 6.
    Bergman, Niclas
    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.
    Probabilistic serviceability limit statedesign approach for dry deep mixingManuscript (preprint) (Other academic)
  • 7.
    Bista, Dipen
    et al.
    SINTEF Narvik AS, N-8517 Narvik, Norway.;Norwegian Univ Sci & Technol NTNU, N-7491 Trondheim, Norway.;SINTEF Narvik AS, N-8517 Narvik, Norway.;Norwegian Univ Sci & Technol NTNU, N-7491 Trondheim, Norway..
    Sas, Gabriel
    SINTEF Narvik AS, N-8517 Narvik, Norway.;SINTEF Narvik AS, N-8517 Narvik, Norway..
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Lia, Leif
    Norwegian Univ Sci & Technol NTNU, N-7491 Trondheim, Norway.;Norwegian Univ Sci & Technol NTNU, N-7491 Trondheim, Norway..
    Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load2020In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 12, no 3, p. 449-460Article in journal (Refereed)
    Abstract [en]

    The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.

  • 8.
    Bjureland, William
    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.
    Sjölander, Andreas
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Probability distributions of shotcrete parameters for reliability-based analyses of rock tunnel support2019In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 87, p. 15-26Article in journal (Refereed)
    Abstract [en]

    A common support measure for underground excavations in jointed rock masses to support loose blocks is to apply a thin shotcrete layer to the periphery of the excavation and systematically install rockbolts into the surrounding rock mass. In this support system, large blocks are carried by the rockbolts and small blocks are carried by the thin shotcrete layer. To verify the shotcrete layer's load-bearing capacity and to stringently account for the large uncertainties incorporated in the variables involved in determining its capacity, analytical calculations in combination with reliability-based methods can be used. However, a lack of knowledge exists regarding the magnitude and uncertainty of shotcrete characteristics (thickness, adhesion, flexural tensile strength, residual flexural tensile strength, and compressive strength), making it difficult to apply reliability-based methods. A statistical quantification of these characteristics is therefore important to facilitate reliability-based methods in design and verification of shotcrete support. In this paper, we illustrate how shotcrete support against small loose blocks can be viewed as a correlated conditional structural system and how this system can be analyzed using reliability-based methods. In addition, we present a unique amount of data for the aforementioned variables, which are all incorporated in the design and verification of a shotcrete layer's ability to sustain loads from small loose blocks. Based on the presented data, we statistically quantify and propose suitable probability distributions for each variable. Lastly, we illustrate how the proposed probability distributions can be used in the design process to calculate the probability of exceeding the shotcrete's load-bearing capacity. Both the probabilistic quantification and the defined correlated conditional structural system along with the illustrative calculation example are followed by a discussion of their implications.

  • 9.
    Bjureland, William
    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.
    Spatial Variability of Shotcrete Thickness in Design of Rock Tunnel SupportManuscript (preprint) (Other academic)
  • 10.
    Bjureland, William
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Dimensionering av sprutbetongförstärkning för lösa block med sannolikhetsbaserade metoder2020Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    An accepted design approach according to the Eurocodes is the use of reliability-based methods. By using reliability-based methods, uncertainties are stringently accounted for by assigning probability distributions to all input parameters. Structural safety is ensured by verifying that the probability of exceeding the structural capacity is smaller than the target probability specified by the Eurocodes. An obstacle for the applicability of reliability-based methods for design of shotcrete support against small loose blocks, has been that insufficient amount of data have been available to assign probability distributions for the relevant input parameters. Additionally, the shotcrete’s failure modes are conditioned and correlated to each other and the shotcrete must therefore be analyzed as a structural system, which have not been performed in previous studies. In this paper, the results from a PhD-project financed by SBUF, BeFo, SVC, and SKB are presented. Based on the aforementioned aspects, a reliability-based design method for shotcrete support against loose blocks is presented. Initially, probability distributions are presented for the shotcrete parameters, based on a large amount of data from The Stockholm City Line. Afterwards, the developed design methodology is presented, in which an initial design is performed before the start of construction and, during construction, the applied shotcrete’s load-bearing capacity is verified using control measurements from the field and Bayesian statistics.

  • 11.
    Bjureland, William
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Influence from spatially varying thickness on shotcrete’s load-bearing capacityManuscript (preprint) (Other academic)
  • 12.
    Bjureland, William
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. KTH Royal Inst Technol, Dept Civil & Architectural Engn, SE-10044 Stockholm, Sweden..
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Influence of spatially varying thickness on load-bearing capacity of shotcrete2020In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 98, article id 103336Article in journal (Refereed)
    Abstract [en]

    A common approach to verify a shotcrete layer's ability to secure blocks that can exist between rockbolts in a tunnel is to use analytical calculations. For this situation, an attractive approach to account for variability in the shotcrete parameters is to use reliability-based methods. Variability can then be accounted for by assigning suitable probability distributions to all relevant input parameters. Structural safety can be ensured by verifying that the probability of limit exceedance is smaller than an acceptable target probability of failure. However, even though analytical calculations and reliability-based methods can be used to design shotcrete support, one of the commonly made basic assumptions is that the load-bearing capacity of the shotcrete is governed by the spatial average of the input parameters. Thus, the spatial variability of the parameters are neglected. As a result, if the capacity is governed by the lowest value of a certain parameter, this assumption is non-conservative. In this paper, we present a novel approach in which the minimum of either the spatial average of a shotcrete slab of varying thickness, or the spatial average along the periphery of a loose block of that same slab, is used to estimate the load-bearing capacity of the shotcrete in a tunnel. The approach is based on results from numerical simulations of a shotcrete slab that we perform to investigate the effect that a spatially varying thickness has on the flexural load-bearing capacity of the slab. The results from the simulations show that the shotcrete's flexural load-bearing capacity might be overestimated when using the spatial average of shotcrete thickness between four rockbolts in design. Using the presented approach, the spatial variability of shotcrete thickness can be accounted for in practical design of tunnels without complex and time-consuming numerical simulations.

  • 13.
    Bjureland, William
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Reliability-based design principles of shotcrete support for tunnels in hard rockManuscript (preprint) (Other academic)
  • 14.
    Bjureland, William
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Prästings, Anders
    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.
    Challenges in applying fixed partial factors to rock engineering design2017In: Geotechnical Special Publication, ISSN 0895-0563, no 283, p. 384-393Article in journal (Refereed)
    Abstract [en]

    The Swedish national guidelines for design of the main structural support system in road and railway rock tunnels have been adjusted to cohere with Eurocode 7. In the design guidelines, the limit states that the designer should consider are specified. The main method to account for uncertainties in the Swedish guidelines is similar to the method preferred in Eurocode 7: the partial factor method. For each limit state, fixed partial factors retrieved from different sections of the Eurocodes are specified. However, fixed partial factors may not correspond to the same structural reliability for all design situations. In this paper, we show for a common design situation in rock engineering design how partial factors in theory should vary with design geometries and uncertainties. The derived partial factors are compared to the Eurocodes’ fixed values. We find that using fixed partial factors to ensure structural safety in these limit states might not be suitable. The implications are discussed along with suggestions of other more suitable methods to account for uncertainties in rock engineering design.

  • 15.
    Bjureland, William
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Prästings, Anders
    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.
    Reliability aspects of rock tunnel design with the observational methodManuscript (preprint) (Other academic)
  • 16.
    Bjureland, William
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Spross, Johan
    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.
    Prästings, Anders
    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.
    Reliability aspects of rock tunnel design with the observational method2017In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 98, p. 102-110Article in journal (Refereed)
    Abstract [en]

    According to Eurocode 7, two accepted approaches for managing uncertainty in tunnel design are reliability based methods and the observational method. Reliability-based methods account for uncertainty by acknowledging the random variation of the input parameters; the observational method does this by verifying the expected behavior from an initial design during the course of construction. However, in the framework of the observational method, as defined in Eurocode 7, no guidance is given on the selection of suitable parameters for observation and how they can be linked to the limits of acceptable behavior and, at a sufficiently early stage, the decision for implementing contingency actions. Furthermore, no guidance is given on how to verify that the structure fulfills society's required safety level. In this paper, we present a design procedure for shotcrete-supported rock tunnels that combines reliability-based methods with the observational method. The design procedure applies a deformation-based limit state function for the shotcrete support that is based on the convergence confinement method. We suggest how the requirements in the observational method, as defined in Eurocode 7, may be satisfied for this application. In particular, we focus on the structural reliability aspects. The structural reliability of the preliminary design is assessed with Monte Carlo simulations by calculating the expected deformations of the tunnel. The appropriateness of the preliminary design is then verified by observing the actual deformations during the course of construction. The observed deformations are used to predict the future behavior of the tunnel and to update the assessed probability of unsatisfactory behavior. If the defined deformation-based alarm limit regarding the structural reliability is exceeded, predefined contingency actions are put into operation. The procedure is illustrated with a shotcrete-lined circular rock tunnel and practical aspects in satisfying the reliability requirements with the observational method are discussed.

  • 17.
    Bjureland, William
    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).
    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.
    Some aspect of reliability-based design for tunnels using observational method (EC7)2015In: EUROCK 2015 & 64th Geomechanics Colloquium, Salzburg, 2015Conference paper (Refereed)
    Abstract [en]

    According to Eurocode 7, the observational method is an accepted design method, where a preliminary design may be updated as the construction progresses. However, Eurocode 7 does not give any advice on how to relate the observations to the acceptable level of safety of the structure. In this paper, we outline a methodology for how to use deformation measurements to predict the final deformation of a circular rock tunnel to calculate the probability of failure. Consequently, the measurements can be used to verify that the design does not violate the specified safety level. The paper shows the potential of combining the observational method with reliability-based design in tunneling

  • 18.
    Damasceno, Davi Rodrigues
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Effect of rock joints on lined rock caverns subjected to high internal gas pressure2023In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 15, no 7, p. 1625-1635Article in journal (Refereed)
    Abstract [en]

    The storage of hydrogen gas in lined rock caverns (LRCs) may enable the implementation of the first large-scale fossil-free steelmaking process in Sweden, but filling such storage causes joints in the rock mass to open, concentrating strains in the lining. The structural interaction between the LRC components must be able to reduce the strain concentration in the sealing steel lining; however, this interaction is complex and difficult to predict with analytical methods. In this paper, the strain concentration in LRCs from the opening of rock joints is studied using finite element (FE) analyses, where the large- and small-scale behaviors of the LRC are coupled. The model also includes concrete crack initiation and development with increasing gas pressure and rock joint width. The interaction between the jointed rock mass and the reinforced concrete, the sliding layer, and the steel lining is demonstrated. The results show that the rock mass quality and the spacing of the rock joints have the greatest influence on the strain distributions in the steel lining. The largest effect of rock joints on the maximum strains in the steel lining was observed for geological conditions of “good” quality rock masses.

  • 19.
    Damasceno, Davi Rodrigues
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Reliability-based design methodology for lined rock cavern depth using the response surface method2020In: ISRM International Symposium - EUROCK 2020, International Society for Rock Mechanics , 2020Conference paper (Refereed)
    Abstract [en]

    Efforts to decrease CO2 emissions in the Swedish steelmaking process involve the use of industrial quantities of hydrogen gas supplied from large-scale Lined Rock Cavern (LRC) storages in order to eliminate the use of fossil fuels. This storage must be placed at sufficient depth so that the overburden is able to resist the uplifting gas pressure from inside the cavern. Both the high reliability requirement and addressing the uncertainties related to the rock mass properties make it difficult to design for such structures. In this work, a reliability-based design methodology for the LRC depth specification using the Response surface (RS) method is presented. Geologic conditions of Sweden, i.e. hard rock, are considered and the analytical solution for the resistance to uplift includes the tensile strength of the failure surface in addition to the overburden weight pressure. The highest uncertainties are assumed to be related to the rock mass parameters and both the cavern radius and the maximum operational pressure are chosen to be the same as for the LRC in Skallen, in southwestern Sweden. Four random variables with varying correlation are used to estimate the acceptable cavern depth and the results are reasonable compared to previous experience. The efficiency of the RS method for the considered problem is observed both for required number of samples and accuracy, showing suitability to be used with more complex, difficult to evaluate, problems such as Finite Element models.

  • 20.
    Damasceno, Davi Rodrigues
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Reliability-based design tool for gas storage in lined rock caverns2023In: Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, ISSN 1749-9518, E-ISSN 1749-9526, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The transition to a fossil-free energy matrix may require large quantities of hydrogen gas, which could be stored efficiently in an underground lined rock cavern (LRC). Since the consequences of failure can be catastrophic, the LRC design needs to have a small probability of failure. However, the current design practice for LRCs is deterministic, which limits the possibility to stringently address geotechnical uncertainties in the design. In this paper, a reliability-based design tool is presented for LRCs. The adaptive directional importance sampling (ADIS) method, which requires a relatively small number of samples, is used with a 3D finite element (FE) model to evaluate small probabilities of failure. An illustrative example based on the LRC in Skallen, southwestern Sweden, demonstrates the implementation and applicability of the developed design tool. The considered uncertainties are related to the geological conditions and the steel lining. The results show that the reliability of this LRC design meets the expected safety requirements. Considering different geological conditions with correlations, at least “good” quality rock mass is needed for the LRC design. An additional sensitivity analysis is performed to study the potential influence of corrosion and hydrogen embrittlement on the reduction of the LRC design reliability.

  • 21.
    Damasceno, Davi Rodrigues
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rock mass response for lined rock caverns subjected to high internal gas pressure2023In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 15, no 1, p. 119-129Article in journal (Refereed)
    Abstract [en]

    The storage of hydrogen gas in underground lined rock caverns (LRCs) enables the implementation of the first fossil-free steelmaking process to meet the large demand for crude steel. Predicting the response of rock mass is important to ensure that gas leakage due to rupture of the steel lining does not occur. Analytical and numerical models can be used to estimate the rock mass response to high internal pressure; however, the fitness of these models under different in situ stress conditions and cavern shapes has not been studied. In this paper, the suitability of analytical and numerical models to estimate the maximum cavern wall tangential strain under high internal pressure is studied. The analytical model is derived in detail and finite element (FE) models considering both two-dimensional (2D) and three-dimensional (3D) geometries are presented. These models are verified with field measurements from the LRC in Skallen, southwestern Sweden. The analytical model is inexpensive to implement and gives good results for isotropic in situ stress conditions and large cavern heights. For the case of anisotropic horizontal in situ stresses, as the conditions in Skallen, the 3D FE model is the best approach.

  • 22.
    Damasceno, Davi Rodrigues
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Jan
    Naturgasteknik.
    Efficiency of subset simulation in the design of lined rock caverns for storage of hydrogen gas2019In: Proceedings of the 13th International Conference on Applications of Statistics and Probability in Civil Engineering, Seoul, South Korea, 2019, article id 124Conference paper (Refereed)
    Abstract [en]

    Efforts to substitute the use of fossil fuels in industry by hydrogen gas requires the storage of large volumes of gas with a reliable pressure vessel design. The Hydrogen Breakthrough Ironmaking Technology (HYBRIT) initiative aims to make the whole steel making process in Sweden fossil-free with the storage of industrial scale quantities of hydrogen in underground Lined Rock Cavers (LRCs). The LRC concept is a relatively new design methodology that can be further developed with respect to safety and economic efficiency and reliability-based design methods provide one option to comply with codes and regulations. High reliability is required for the storage of hydrogen gas and the computational time becomes unpractical for the evaluation of a complex system such as the LRC. In this paper, the efficiency of Subset Simulation (SuS) regarding accuracy, precision and required number of samples is studied for the calculation of probability of failure against fatigue of the steel lining. It can be observed that by increasing the number of samples per level and increasing the conditional probability of failure the precision increases as well as the total number of samples. The accuracy of the SuS is checked with respect to Monte Carlo simulation (MCS) showing good agreement and with greater precision for fewer number of samples. A case study is performed for the geologic conditions of Sweden showing that the considered failure mode is unlikely for high stresses and good rock mass quality.

  • 23.
    Draganović, Almir
    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.
    Svällande leror i bergtunnlar - Förstudie2010Report (Other academic)
  • 24.
    Elsayed, Ahmed
    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.
    Verification of a conceptual model for the shear strength of rock joints with different degrees of matedness2012In: Bergmekanikdagen 2012, 2012Conference paper (Other academic)
  • 25.
    Ghazal, Rima
    et al.
    Itasca .
    Mas Ivars, Diego
    Itasca.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Batres-Estrada, Rocio
    SWECO Civil AB.
    Back analysis of in situ stress at shallow depth using discontinuum numerical modeling - a case study at the Odenplan station in Stockholm, Sweden2015Conference paper (Refereed)
  • 26. Gustafsson, A
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Krounis, Alexandra
    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.
    Krokströmmen valvdamm, stabilitetsanalys i 3D / Stability analysis of the arch dam at Krokströmmen2010Conference paper (Other academic)
  • 27. Gustafsson, A
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Löwen, K-E
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Analysis, instrumentation and upgrading of the Krokströmmen Arch Dam2010In: Dam Safety: Sustainability in a Changing Environment, 2010Conference paper (Refereed)
  • 28. Gustafsson, A
    et al.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rytters, K
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Sliding stability analyses of concrete gravity dams founded on rock: proposal for new Swedish guidelines2009Conference paper (Refereed)
  • 29. Gustafsson, Anders
    et al.
    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.
    Betongdammas glidstabilitet: Förslag på nya riktlinjer2008Report (Other academic)
  • 30.
    Hellgren, Rikard
    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.
    Fransson, Lennart
    Luleå University of Technology.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Measurement of ice pressure on a concrete dam with aprototype ice load panelManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents the development and installation of a prototype ice load panel andmeasurements of ice load from February 2016 to February 2018 at the Rätan hydropower damin Sweden. The design of the 1x3 m2 panel enabling direct measurement of ice pressure on theconcrete surface is based on previous experience from similar measurements with sea ice.Important features of the design are sufficient height and width to reduce scale effects and tocover the ice thickness and variations in water level. The Rätan dam was chosen based onseveral criteria so that the ice load is considered to be reasonably idealized against the damstructure.For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations duringthe cold winter months, and the daily peak ice loads showed a visual correlation with the dailyaverage temperature and with the daily pattern of operation of the power station with itscorresponding water level variations

  • 31.
    Hellgren, Rikard
    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.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Luleå, Sweden.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Measurement of ice pressure on a concrete dam with a prototype ice load panel2020In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 170, article id 102923Article in journal (Refereed)
    Abstract [en]

    This paper presents the development and installation of a prototype ice load panel and measurements of ice load from February 2016 to February 2018 at the Rätan hydropower dam in Sweden. The design of the 1 × 3 m2 panel enables direct measurement of ice pressure on the concrete surface is based on previous experience from similar measurements with sea ice. Important features of the design are sufficient height and width to reduce scale effects and to cover the ice thickness and variations in water level. The Rätan dam was chosen based on several criteria so that the ice load is considered to be reasonably idealized against the dam structure.

    For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161 kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations during the cold winter months, and the daily peak ice loads showed a visual correlation with the daily average temperature and with the daily pattern of operation of the power station with its corresponding water level variations.

  • 32.
    Hellgren, Rikard
    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.
    Ríos Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Pull-out tests of 50-year old rock bolts2016In: Proceedings of the International Symposium on Appropriate technology to ensure proper Development, Operation and Maintenance of Dams in Developing Countries, Johannesburg, 2016, p. 263-272, article id 258Conference paper (Refereed)
    Abstract [en]

    In this paper, detailed numerical and analytical calculations are presented with the aim to study the effect of rock bolts and the influence of degradation on the dam safety. In addition, results from inspections and pull-out tests are presented from a case study with rock bolts that has been installed for 50 years. All tested bolts have with margin withstood higher stresses than the maximum allowed stresses according to Swedish standards. At visual inspection, no bolts have shown any major signs of degradation and all investigate bolts are in very good condition.

  • 33.
    Hoeft, Madeleine
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Kronsell, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Manzoor, Sohail
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. KTH.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    von Haslingen, Tobias
    ConcretePrint.
    Eriksson, Kent
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Real Estate Business and Financial Systems.
    Construction Automation and Robotics in Infrastructure2022Report (Other academic)
    Abstract [en]

    In Sweden, as in many other countries, the construction andinfrastructure sector are of large and growing importance for the economyand society. For instance, the construction industry’s turnover equals 11% ofthe Swedish gross domestic product (GDP) (Byggföretagen 2021), and theSwedish Transport Administration plans to invest SEK 799 billion during theperiod 2022-2033 (Regeringen 2021). At the same time, the cost ofinfrastructure projects has increased more than the consumer price index(CPI) (Trafikverket (2021)), partly due to a poorer development of theproductivity compared to other industries. An improved productivity andefficiency in the transport infrastructure and construction industry istherefore necessary. One way to increase productivity, improve theoccupational health and safety, and sustainability is through automation anddigitalization of the construction industry.The aim of the present report has been to identify ongoing initiatives andexisting research trends in construction automation with a focus on civilengineering, both nationally and internationally; and to identify potentialsand challenges that exist for the development of construction automation.Furthermore, the prerequisites for the implementation of automation in theconstruction industry have been studied. The research questions were studiedthrough a literature study and two thematic days on the subject.The results from the literature study shows that a clear increasing trendexists, both nationally and internationally, in automation, digitization androbotisation in the construction industry. The same trend can also be seen incivil engineering for roads, bridges, tunnels, as well as in the mining industry.With the mining industry as a role model, construction companies,universities, suppliers and clients together with small and medium-sizedenterprises (SMEs) should come together to develop a common vision and astrategic roadmap to enforce automation and digitization of the constructionindustry. A development of both technical, organizational and financialstructures is required, where an attractive business ecosystem can bedeveloped, enabling the upscaling of construction automation.Interdisciplinary collaborations, test-beds at an early stage, competencedevelopment, new financing infrastructure and a common vision are crucialto create conditions for construction automation.

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  • 34.
    Ivars, Diego Mas
    et al.
    SKB.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ghazal, Rima
    Itasca Consultants SAS.
    Sánchez Juncal, Abel
    Itasca Consultants AB.
    Batres Estrada, Rocío
    AECOM.
    A case study of the Odenplan station in the Stockholm City Link project - Analysis of in situ stresses and observed ground behaviour.2016Report (Refereed)
    Abstract [en]

    The Odenplan Station in the Stockholm City Link project is located directly under theexisting subway station with a minimum rock cover of approximately 7 m. The span of theOdenplan Station is 25 m. When the Odenplan station was excavated, deformations largerthan anticipated in previous calculations were observed. The main reason for this discrepancyis believed to be high horizontal in situ and/or persistent fractures in the area parallel withthe excavation.The excavation of the Odenplan station constitutes a case study with well-documented rockmass characteristics, excavation sequences, support sequences and measured deformations.It therefore provides a unique project to analyse. Based on this case study, the main objectivesof this study was to (1) suggest a general technique for numerical back analyses based onmeasured deformations under geological conditions as those present in the Stockholm area,and (2) analyse the range of possible in situ stresses at Odenplan Station in the City Linkproject.The complex three-dimensional 3DEC model lead to rather long computational times. Ageneral technique for a real back analysis was therefore not possible to obtain in this study,since it would require unrealistically long computational time. Instead, a sensitivity study onthe in situ stresses and different types of continuum and discontinuum approaches wereperformed. The results from the analyses gave valuable insight into which types of modelsthat were able to properly recreate the observed ground behavior at Odenplan. The resultsfrom the study clearly showed that a continuum approach does not capture the true behaviorof the blocky rock mass at Odenplan. It is therefore recommended that discontinuumapproaches are used in the future when structurally controlled block movements could beexpected. However, the exact cause behind the discrepancy between the continuum and thediscontinuum model has not been determined in this report.The performed sensitivity analysis suggests that the in situ stresses are high and in the rangeof those previously measured. Maximum horizontal in situ stresses are probably in the rangeof 5.7-7.2 MPa at a depth of 0-20 m, which agrees well with the results of previous rockstress measurements, which were, on average, 8.1 MPa at a depth of 30 m.The encouraging results from this project indicate that further stress sensitivity analysesshould be performed to have a better estimation of the range of in situ stresses in theStockholm area by fitting displacements obtained from modeling to those measured in situ in different projects. These analyses are important in order to understand our present abilityto perform numerical simulations reflecting true rock mass behavior.

  • 35. 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.

  • 36.
    Johansson, Fredrik
    KTH, Superseded Departments (pre-2005), Civil and Architectural Engineering.
    Grundläggning på berg med tunga konstruktioner: ett grundläggande problem2004In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, no 1, p. 36-40Article in journal (Other (popular science, discussion, etc.))
  • 37.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Influence of scale and matedness on the peak shear strength of fresh, unweathered rock joints2016In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 82, p. 36-47Article in journal (Refereed)
    Abstract [en]

    It is widely recognized that the mechanical parameters for unfilled and rough rock joints, such as the peak shear strength, can vary with scale. However, due to contradictory results concerning the extent and nature of the scale effect reported in the literature, it is still a debated subject. A conceptual model developed by Johansson and Stille 2014 suggests how roughness and matedness at different scales influences the peak shear strength for fresh, rough and unweathered joint. However, the model's ability to predict how the roughness and matedness affects the peak shear strength at different scales was not verified. The aim of this paper is to investigate the ability of the conceptual model to estimate the peak shear strength at different degrees of matedness and scales. A series of direct shear test were carried out at two different scales and two different degrees of matedness. The peak shear strength from the tests was compared to the peak shear strength calculated with the conceptual model. The results showed that the model can predict the peak shear strength for both the perfectly mated and the unmated joints. No scale effect was observed in the shear tests, which is in line with the predictions using the model. The influence of matedness in combination with scale might explain some of the contradictory findings regarding the scale effect.

  • 38.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Inverkan från skala och passning på skjuvhållfastheten för råa bergsprickor2014Conference paper (Other academic)
  • 39. Johansson, Fredrik
    Inverkan från skala och passning på skjuvhållfastheten för råa ofyllda sprickor2013Report (Other academic)
  • 40.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Managing uncertainties in sliding stability re-assessment of concrete dams founded on rock2020In: ISRM International Symposium - EUROCK 2020, International Society for Rock Mechanics , 2020Conference paper (Refereed)
    Abstract [en]

    Many of the concrete dams in the western world today have reached a considerable age. With an ageing population of dams, re-assessment of their structural safety is becoming increasingly important to ensure that failure does not occur because of material deterioration in the dam body or foundation. But re-assessing the current safety of an existing dam is many times more difficult than ensuring that a dam-to-be-built satisfies all safety criteria. In sliding stability re-assessment of concrete dams, sliding along potential weakness planes in the rock foundation is an important failure mode that needs to be addressed. However, the parameters governing the shear strength of this failure mode are associated with large uncertainties and are difficult to assess due to the existing dam. This keynote paper presents a summary of the work performed at the Division of Soil and Rock Mechanics, KTH Royal Institute of Technology on this topic during the last decade by the author and colleagues. The main massage is that a combination of reliability-based design, statistical decision theory and observations through investigations and testing are key tools to obtain optimal decisions for acceptable dam safety in the re-assessment of existing concrete dams.

  • 41.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Shear Strength of Unfilled and Rough Rock Joints in Sliding Stability Analyses of Concrete Dams2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The horizontal water load combined with uplift forces implies that concrete damsare sensitive for sliding. At the same time, the safety of concrete dams againstsliding in the rock foundation is associated with large uncertainties. One of themain uncertainties regards the shear strength of rock joints.

    Several failure criteria exist to express the shear strength for unfilled and roughrock joints. However, these criteria do not in general consider a possible scaleeffect which means that the shear strength could be lower at larger scales. Somesuggestions exist for how a possible scale effect could be considered, but theseare mainly based on empiric grounds. This means that there exists a need of amore detailed and conceptual understanding on the scale effect of rock joints.

    In an attempt to increase the understanding on the scale effect of unfilled andrough rock joints, a conceptual model was derived. The model is based on theassumptions that contact points occur at the steepest asperities facing the sheardirection and that their total area could be expressed with adhesion theory. Fractaltheory is used in order to idealize the surface roughness by superposition ofasperities at different scales. Based on changes in the size and number of contactpoints, the conceptual model suggests that the scale effect does not occur for alltypes of rock joints. Perfectly mated joints are suggested to not exhibit any scaleeffect while a considerable scale effect could be expected for unmated joints.

    The practical implications from this, for foundations with unfilled joints, is thatunmated joints with large aperture are most critical for the sliding stability ofconcrete dams, since these joints probably are the ones with longest persistenceand lowest shear strength.

    In order to study the scale effect of rock joints further, eighteen shear tests atdifferent scales were performed. All of the samples were taken from the rockfoundation at Långbjörn hydropower station. Possible scale effects could beobserved, but no firm conclusions could be made, mainly due to different surfacecharacteristics of the tested joints. Three of the samples were also used toinvestigate the accuracy of the conceptual model. This investigation revealed thatit may be necessary to distinguish between weathered and unweathered joints,since the distribution of contact points appears to become more randomlydistributed for a weathered joint which in turn results in lower friction angles.

    In Sweden, dam safety is governed by the Swedish power company’s guidelinesfor dam safety, RIDAS. When the Swedish guidelines were compared withguidelines and regulations in other countries, it was realized that there exists aneed for a more balanced evaluation of the sliding stability for concrete damsfounded on rock in Sweden. In a first step of development, it can be based onsafety factors and an increased use of investigations. However, in a second step, anatural way of the development of RIDAS would be in a direction towardsreliability based methods.

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  • 42.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Skjuvhållfasthet för råa och ofyllda bergsprickor2009Report (Other academic)
  • 43.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stabilitetsanalyser av stora konstruktioner grundlagda på berg: En inledande litteraturstudie2006Report (Other academic)
  • 44.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stabilitly analysis of large structures founded on rock: an introductory study2005Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Previous investigations of Swedish and international dams have shown difficultiesto assess the safety against failure in rock foundations. The problem was alsogiven additional interest in connection to the recent construction of the newbridge at Traneberg in Stockholm. This project was created in order to increasethe knowledge in the subject of stability analysis of large structures founded onrock, and how they should be performed in order to describe the safety in areliable way.

    This thesis covers the first half of this project. The objectives of the thesis were todescribe the knowledge and current state of practice in the subject with a literaturestudy, and with a case study of the arch dam at Krokströmmen show the problemsfor stability analyses where foundation and structure interact. The objective wasalso to produce a foundation for future work.

    At Krokströmmen arch dam, previous three dimensional finite element analyseshave been performed (Johansson and Palmgren 1996). In these analyses, thestiffness of the foundation was not considered. Based on the results from theseanalyses, stability was analytically analyzed for each monolith by Stille et al.(2002). The results indicated low factors of safety for the central monoliths. As aconsequence, a reinforcement slab was constructed to increase stability.

    In order to show how varying stiffness and non-linear resistance of the foundationaffects stability, a quasi three dimensional finite element analyses were carriedout. In these analyses, five of the central monoliths were first analyzed separately.Thereafter, the reaction forces were adjusted to fit the results from the analyses byJohansson and Palmgren (1996). The monoliths were thereafter coupled togetherwith assumptions of equal deformations and constant total reaction forces for thefive monoliths. Through an iterative procedure, constant deformation and newredistributed reaction forces were obtained. These forces were used to discuss thestability for one of the monoliths in detail.

    This thesis shows that the problem is more complex than described in the Swedishdam safety guidelines, RIDAS (Svensk Energi 2002), and the Swedish bridgedesign code, BRO 2004 (Vägverket 2004). An accurate analysis of the stability ina rock foundation under large structures demands a more refined approach, whichconsiders the specific features associated with rock mechanical problems. Thecase study showed that the interaction between foundation and structure can beconsiderable; deformations and reaction forces acting on the foundation wereredistributed when the stiffness of the foundation was considered. Furthermore,the resistance is a function of deformation. These aspects are necessaryconsidering if stability should be determined with high confidence.

    An additional question which was identified and brought up for discussion wasthe possibility of time-dependent deformation in the foundation at Krokströmmendue to creep and cyclic loading, which in turn can affect the long term stability.

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  • 45.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Bagheri, Mehdi
    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.
    Variation of mechanical parameters of a slightly weathered joint in granite estimated from fourteen shear tests2010In: ROCK MECHANICS IN CIVIL AND ENVIRONMENTAL ENGINEERING, 2010, p. 223-226Conference paper (Refereed)
    Abstract [en]

    Describing the mechanical parameters of a rock joint with single values is difficult since rock has a natural spatial variation. In addition to this, the interpretation of the results is dependent on the number of tests. Despite this fact, input data for these parameters are often given with a deterministic value. This paper presents the results of fourteen shear tests tested under a constant normal stress of approximately 0.8 MPa. The samples were taken from a slightly weathered rock joint in granite. Basic friction angle and dilation angle, together with shear and normal stiffness, are evaluated. Based on the results, mean values and standard deviations together with coefficient of variations for the different parameters are presented. After that, different statistical distributions for the parameters are compared. Finally, the results are compared against calculated values derived from commonly used equations.

  • 46.
    Johansson, Fredrik
    et al.
    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.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Application of Reliability-based Design Methods to Underground Excavation in Rock2016Report (Other academic)
  • 47.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Edeskär, Tommy
    Luleå Tekniska Universitet.
    Reparationsinjektering av dammar och undergrund: strategi för forskning och utveckling2012Report (Other academic)
    Abstract [sv]

    Svenska dammar blir allt äldre och i huvudsak fokuserar industrin på att bibehålla dammarnas funktion och anpassa dem till förändrade förutsättningar och ökade säkerhetskrav. Det är i allmänhet mer komplicerat att reparera eller uppgradera befintliga anläggningar jämfört med att bygga nya. Bygga nytt är i allmänhet orealistiskt vilket innebär att det är angeläget att det finns tillförlitliga metoder tillgängliga för att reparera och uppgradera befintliga anläggningar.Det finns en rad injekteringsmetoder som kan användas för reparation av dammar och undergrund och som prövats internationellt och i viss utsträckning även tidigare i Sverige. Följande metoder har identifierats: kompaktinjektering, permeationsinjektering, inträngningsinjektering och slitsmur. Av dessa metoder har permeationsinjektering identifierats som mest intressant för rehabilitering av medelstora svenska dammar. Inom detta område finns ett antal intressanta forsknings- och utvecklingsspår som är viktiga för branschen.Permeationsinjektering innebär vanligen en användning av en kombination av injekteringsbruk, oftast två olika, för att åtgärda sprickor av olika storlek. Det finns en rad injekteringsbruk tillgängliga men för flera kan beständigheten ifrågasättas eller bör undvikas av miljöskäl. Det finns dock alternativ som bör undersökas närmare och som inte tidigare använts i Sverige, t.ex. silica sol i lösning som aktiveras med kalcium.Vidare behöver en mer ingenjörsbaserad injekteringsmetodik utvecklas och skräddarsys för användning på dammar. Det gäller framförallt vid vilket tryck injekteringen ska utföras för att uppnå ett tillfredsställande injekteringsresultat utan att äventyra dammkonstruktionens säkerhet. Det krävs även bättre kontrollmetoder för brukets spridning under injektering, där forskning rekommenderas inom konceptet ”real time grouting method”. Injektering i strömmande förhållanden och under vattentryck bör också studeras närmare. Särskilt fokus bör läggas på att säkerställa under vilka förhållanden bruket är erosionsstabilt samt att injekteringsskärmarna uppnår de egenskaper som förväntas.Det finns idag bristande erfarenhetsåterföring i Sverige från genomförda reparationsinjekteringsprojekt. Historiska och kommande projekt bör därför dokumenteras inom SVC.

  • 48.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ekström, I.
    Rito Pi, C.
    Malm, Richard
    Carlsson, V.
    FEM-analysis of a concrete dam in northern Sweden2015In: Association of State Dam Safety Officials, Dam Safety 2015, Association of State Dam Safety Officials , 2015Conference paper (Refereed)
    Abstract [en]

    Krångfors is a concrete dam located in northern Sweden that was constructed in three stages from 1928 to 1973. This expansion in different stages resulted in a complicated structural design. Extensive cracks have been noticed in parts of the structure. Two main hypotheses for the cause of these cracks were initially established; 1) alkali-silica reaction (ASR) and 2) large temperature variations in the structure. Petrographic analyses of concrete cores showed that the concrete ballast consisted of greywacke with potential for ASR. However, accelerated testing of concrete cores showed that the potential for expansion due to ASR was limited. To analyze the effect from temperature variations, three dimensional FEManalyses were performed. The results from these FEM-analyses are the main focus of this paper. These analyses showed that adding the annual temperature variation and possible shrinkage to the FEM-model gave results that could explain the observed cracks.

  • 49.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Krounis, Alexandra
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Igensättning av dränage under betongdammar – Orsaker, övervakning och åtgärder: Energiforskrapport 2017:3692017Report (Other academic)
  • 50.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Roslin, Mattias
    Trafikverket.
    Josefsson, Johanna
    Rise.
    Utvärdering av glasfiberbult som permanent bergförstärkning2020Report (Other academic)
    Abstract [en]

    Rock support for tunnels and caverns is usually performed with a combination of conventional steel bolts and shotcrete. The high density of the steel implies that these bolts are rather heavy. At the same time, the installation is performed manually, which can imply a risk from a work environment perspective. The use of bolts consisting of glass-fiber reinforced polymers could reduce these problems since their density is approximately four times lower than that for steel. The aim of this report has been to evaluate if glass-fiber reinforced rock bolts fulfill the requirements for permanent rock support and recommend possible further studies necessary for approval of these types of bolts as construction elements in the main load bearing system. After studying the results from Swedish and international research, the conclusion is that glass-fiber reinforced rock bolts could be suitable in the future under certain conditions, which mainly consists of a rock mass of good quality where block instability is the main failure mode and the expected strain in the rock mass is limited. At the present time, the information is insufficient and further knowledge is required before an approval of glass-fiber reinforced rock bolts should be given. The main cause is that there exists uncertainties concerning the combined effect from static long-term loading and the influence from environmental factors such as water and alkali. Further research is recommended in order to reduce these uncertainties and enable the use of glass-fiber reinforced rock bolts as construction elements in the main load bearing system. By doing so, an improved working environment and a reduced environmental impact could be achieved.

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