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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: The Electronic journal of geotechnical engineering, ISSN 1089-3032, 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 & teknik, ISSN 0281-658X, 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.
    Storskalig kartering av skredbenägenhet i västra Götaland med artificiell intelligens2018Conference paper (Other academic)
  • 5.
    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)
  • 6.
    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.

  • 7.
    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)
  • 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.
    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)
  • 9.
    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.

  • 10.
    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)
  • 11.
    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.

  • 12.
    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

  • 13.
    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.

  • 14.
    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)
  • 15.
    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)
  • 16.
    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)
  • 17. 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)
  • 18. 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)
  • 19. 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)
  • 20. 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)
  • 21.
    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

  • 22.
    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.

  • 23.
    Ivars, Diego Mas
    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.
    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.

  • 24.
    Johansson, Fredrik
    KTH, Superseded Departments, Civil and Architectural Engineering.
    Grundläggning på berg med tunga konstruktioner: ett grundläggande problem2004In: Bygg & teknik, ISSN 0281-658X, no 1, p. 36-40Article in journal (Other (popular science, discussion, etc.))
  • 25.
    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.

  • 26.
    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)
  • 27. Johansson, Fredrik
    Inverkan från skala och passning på skjuvhållfastheten för råa ofyllda sprickor2013Report (Other academic)
  • 28.
    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.

  • 29.
    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)
  • 30.
    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)
  • 31.
    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.

  • 32.
    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.

  • 33.
    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)
  • 34.
    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.

  • 35.
    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.

  • 36.
    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)
  • 37.
    Johansson, Fredrik
    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.
    Damasceno, Davi
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Jan
    Naturgasteknik AB.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Investigation of research needs regarding the storage of hydrogen gas in lined rock caverns: Prestudy for Work Package 2.3 in HYBRIT Research Program 12018Report (Other academic)
    Abstract [en]

    The objective of HYBRIT RP1 is to explore and assess pathways to fossil-free energy-mining-iron-steel value chains and thereby provide a basis for industrial development activities and the necessary future transformative change in this field. A large-scale storage capacity for hydrogen gas is an important component of the proposed HYBRIT concept. Underground storage in lined rock caverns provides a reasonable option: a large-scale demonstration plant for storage of natural gas was constructed in Sweden in 2002 and has operated safely since then. Considering that this lined rock cavern facility was constructed for natural gas, the present report investigates the current research needs to allow for underground storage of hydrogen gas in such a facility. This will serve as a basis for the research in Work Package 2.3 of HYBRIT RP1.

    Studying the experiences from decades of Swedish and international research and practice on the construction of underground gas storage facilities, the conclusion is that the lined rock cavern concept seems a reasonable way forward. In terms of rock engineering research, there are currently no critical research issues; however, a development of a previously proposed risk-based design framework for lined rock caverns may further strengthen the ability to manage risks related to underground gas storage facilities. The report identifies several potential research questions on this topic to be further studied: development of a risk-based design approach using subset simulation, the optimization potential of the concrete thickness in the lining, and the effect of spatial variation of rock mass properties on a location’s suitability for the storage facility.

    Additionally, the report identifies the potential effect of hydrogen embrittlement on the steel lining as a critical research issue to ensure safe storage of hydrogen gas in lined rock caverns. However, as this issue is not related to rock engineering, but a material issue, it will not be covered further in Work Package 2.3.

  • 38.
    Johansson, Fredrik
    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.
    Fransson, Lennart
    Dammsäkerhet - Islast mot dammkonstruktioner: Sammanställning av kunskapsläget samt förslag till forskning och utveckling2013Report (Refereed)
  • 39.
    Johansson, Fredrik
    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.
    A conceptual model for the peak shear strength of fresh and unweathered rock joints2014In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 69, p. 31-38Article in journal (Refereed)
    Abstract [en]

    Several criteria have been proposed over the years in order to predict the peak shear strength of rock joints.The most widely used criterion is the JRC-JCS criterion by Barton. It says that changes in the peak shear strength originate from surface roughness, joint wall compressive strength and normal stress. A limitation with this criterion is that the contribution from roughness could be overestimated for natural and mismatched joints if the joint roughness coefficient, JRC, is estimated based on the direct profiling method. To account for this effect, Zhao introduced the joint matching coefficient, JMC, which accounts for the matedness of the joint. In addition to this, it is known that the scale of the sheared joint could affect the peak shear strength. However, no criterion exists that describes how roughness, matedness and scale interact. In this paper, a conceptual model is proposed. The model is based on adhesion and fractal theory, measurements of surface roughness and the anticipated variation of the number and size of the contact points. The model proposes how the compressive strength and the roughness of the joint surface together with the matedness of the joint interact in order to form the shear strength of the joint under constant normal load conditions. The model also suggests an explanation for the scale effect of rock joints with respect to the surface roughness.

  • 40.
    Johansson, Fredrik
    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.
    A simplified model for estimation of horizontal rock displacements in connection to Krokströmmen arch dam2004Conference paper (Other academic)
  • 41.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Westberg Wilde, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Probabilistiska metoder för stabilitetsanalys av betongdammar - förslag till framtida utveckling2012Report (Other academic)
  • 42.
    Johansson, Fredrik
    et al.
    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.
    Krounis, Alexandra
    KTH, School of Architecture and the Built Environment (ABE).
    Spross, Johan
    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.
    Some recent developments in reliability based slidingstability assessments for concrete dams2018In: 26th International Congress on Large Dams, 2018, CRC Press/Balkema , 2018, p. 1277-1294Conference paper (Refereed)
    Abstract [en]

    In this paper, a reliability based framework for the assessment of sliding stability for concrete dams was presented. The framework consists of several parts based on the Probabilistic model code for concrete dams developed by Westberg-Wilde and Johansson and includes guidelines on how reliability based sliding stability assessment should be performed, together with recent work by Krounis et al. how to account for partially bonded interfaces. In the proposed framework, the assessments start with performing preliminary calculations using a priori assumptions on parameters included in the analysis. If cost-benefit analyses show that further analyses could be beneficial, investigations are undertaken on relevant parameters in the failure modes. The results from the investigations are used to update the calculations in the assessment and decisions on stability enhancing measures are undertaken if necessary. In the presented example the preliminary sliding stability analysis of the interface, before testing was performed, showed a reliability index of 4.91, indicating an unacceptable failure probability of the dam without any testing. Taking into account the information obtained from testing the basic friction angle of the interface increased the reliability index from 4.91 to 7.24, clearly showing the gain of including test results in the assessment. When the influence of cohesion was accounted for a reliability index of 6.49 was obtained, which shows that cohesion can give a potential gain to the stability, even though it in this case still is lower than the gain from updating the basic friction angle. When both limit states of the interface were considered as a system the reliability index increased to 8.1.

  • 43.
    Krounis, Alexandra
    et al.
    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.
    A comparison between two techniques for including the influence of progressive sliding failure in structural reliability analyses of concrete dams2014In: ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014, International Society for Rock Mechanics , 2014, p. 528-535Conference paper (Refereed)
    Abstract [en]

    The shear strength of concrete-rock interfaces, used in reliability-based analyses of sliding stability of concrete dams, is commonly quantified using a simplified version of the Mohr-Coulomb shear strength criterion. This criterion is based on the assumption of a mean value driven process occurring according to the requirements imposed by perfectly-plastic failure theory. However, tests on cores with bonded interfaces exhibit semi-brittle post-peak behavior, which in combination with a possible spatial variation in cohesion implies that a progressive failure mechanism is a more correct description of the interface behavior. This has to be considered in sliding stability analyses in order to avoid overestimation of dam safety. Uncertainties between model and real behavior like the one described above can be taken into account by introducing a random variable representative of the specific uncertainty into the limit state function. A drawback with this technique is that the real shear strength of the interface is difficult to define since physical observations are not easy to acquire. Krounis and Johansson (2014), therefore, used a technique where numerical analyses were used in order to estimate the real behavior. The technique requires several numerical calculations and is extremely time-consuming. Another, less time-consuming, technique was used by Westberg Wilde and Johansson (2013). In their work, the progressive failure of the bonded interface was taken into account by simulating new distribution parameters for cohesion. This was done by means of an analytical procedure where the cohesive strength of the interface was considered to behave as a brittle parallel system. The stress state of the interface, however, was not considered, which may have significantly affected the results of the analyses. In this paper, a comparison between these two techniques for a hypothetical dam monolith is made in order to study the magnitude of the possible discrepancy between the two techniques. The benefits and limitations of each method are also discussed based on the results of the analyses.

  • 44.
    Krounis, 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.
    Model uncertaintyin sliding stability analyses of concrete gravity dams with bonded concrete-rock interfacesManuscript (preprint) (Other academic)
  • 45.
    Krounis, 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.
    The influence of correlation between cohesion and friction angle on the probability of failure for sliding of concrete dams2012In: Proceedings of the 3rd International Forum on Risk Analysis, Dam Safety Dam Security and Critical Infrastructure Management / [ed] Ignacio Escuder-bueno, Enrique Matheu, Luis Altarejos-garcfa, CRC Press, 2012, p. 75-80Conference paper (Refereed)
    Abstract [en]

    In the latest years there has been a trend towards an implementation of structural reliability analysis, SRA, in the stability assessment of concrete dams. In these analyses, it is in general assumed that the basic variables are independent of each other. However, this may be incorrect. For example, when the shear strength of the bonded concrete-rock interface is approximated with the Mohr-Coulomb failure criterion, the linear approximation of the curved failure envelope implies that a negative correlation between cohesion and friction could be expected. The aim of this paper is to study how correlation between friction angle and cohesion for a bonded interface may affect the sliding stability of concrete gravity dams founded on rock. For this purpose, experimental data from uniaxial and triaxial compressive tests performed on intact rock were used in order to study the existence and magnitude of a possible negative correlation between friction angle and cohesion. After that, the reliability index for a concrete gravity dam was calculated using negatively correlated and uncorrelated friction angle and cohesion. The results showed that the safety index increased significantly as the correlation coefficient decreased. Therefore, in order to calculate the reliability of dams correctly in the future, it is important to study and determine the magnitude of this correlation.

  • 46.
    Krounis, 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.
    Theme C: Estimation of the Probability of Failure of a Gravity Dam for the Sliding Failure Mode2011In: Proceedings of 11th Benchmark Workshop on Numerical Analysis of Dams, 2011, , p. xvi, 34Conference paper (Other academic)
  • 47.
    Krounis, Alexandra
    et al.
    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.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Shear strength of partially bonded concrete-rock interfaces for application in dam stability analyses2016In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, no 7, p. 2711-2722Article in journal (Refereed)
    Abstract [en]

    The shear strength of the concrete–rock interface has a substantial influence on the sliding stability of concrete gravity dams founded on rock. While several studies have been done on concrete–rock contacts, there remains uncertainty regarding the peak shear strength of partially bonded interfaces. There exists, in particular, an uncertainty regarding the contribution from surface roughness of the unbonded parts to the peak shear strength of the interface due to the dependency of mobilized strength on shear displacement. In this study, a series of 24 direct shear tests are performed under CNL conditions on concrete–rock samples with different bonding conditions. Tests on samples with fully bonded and unbonded interfaces are conducted to study the strain compatibility of the different contacts, while the results of samples with partially bonded interfaces are evaluated in the context of linking the joint roughness of the unbonded parts to the peak shear strength of the interface. The results indicate that a significant part of the surface roughness of the unbonded parts is mobilized prior to degradation of bond strength, in particular for interfaces with low bonding percentages. It is recommended that further research should be conducted to understand how the contribution from roughness change with an increase in scale and degree of matedness.

  • 48.
    Krounis, 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.
    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 cohesive strength in probabilstic sliding stability re-assessment of concrete dams2016In: Journal of Geotechnical and Geoenvironmental Engineering, ISSN 1090-0241, E-ISSN 1943-5606, Vol. 143, no 2, article id 04016094Article in journal (Refereed)
    Abstract [en]

    For concrete dams, cohesive strength often constitutes a significant share of the overall shear strength of partially bonded concrete-rock interfaces. However, cohesive strength is also associated with great uncertainties that may have a significant impact on the assessed stability of the analyzed structure. In this paper, the merits of including cohesion are evaluated using a probability-based approach to analyze the sliding stability of an existing concrete gravity dam. The shear strength properties of the interface are inferred from a limited number of site-specific tests and previous knowledge from similar structures using Bayesian updating. The study shows that the potential gain from cohesive strength is strongly related to the involved uncertainties and identifies the bonding percentage and basic friction angle as the most influential parameters. The importance of testing, both with regard to the specific project and for future projects, is also highlighted.

  • 49.
    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.

  • 50.
    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.

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