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  • 1.
    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.

  • 2.
    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)
  • 3.
    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.

  • 4.
    Hov, Sölve
    et al.
    GeoMind/LabMind.
    Prästings, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Persson, Erik
    Bjerking.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    On empirical correlations for normalised shear strengths from fall cone and direct simple shear tests in soft Swedish clays2019In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529Article in journal (Refereed)
  • 5.
    Lingwanda, Mwajuma
    et al.
    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.
    Nyaoro, Dalmas L.
    Comparison of geotechnical uncertainties linked to different soil characterization methods2016In: Geomechanics and Geoengineering, ISSN 1748-6025, E-ISSN 1748-6033, p. 1-15Article in journal (Refereed)
    Abstract [en]

    One of the essential inputs in settlement prediction models is the soil modulus, which may be obtained from laboratory tests or estimated from in situ measurements. The total uncertainty in predicting the confined modulus of a sandy soil is quantified with data from side-by-side in situ testing using the standard penetration test, the static cone penetration test, the light dynamic probing and the laboratory oedometer test. To estimate transformation errors, correlations are proposed between in situ and laboratory data. The results indicate that similar magnitudes of total uncertainties are associated with the in situ methods, which are approximately twice as high as those from the direct oedometer method. The quantified uncertainties are an important input for reliability-based designs of foundations under similar soil conditions.

  • 6.
    Prästings, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Aspects on probabilistic approach to design: From uncertainties in pre-investigation to final design2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Geotechnical engineering is strongly associated with large uncertainties. Exploring a medium (soil) that is almost entirely and completely hidden from us is no easy task. Investigations can be made only at discrete points, and the majority of a specific soil volume is never tested. All soils experience inherent spatial variability, which contributes to some uncertainty in the design process of a geotechnical structure. Furthermore, uncertainties also arise during testing and when design properties are inferred from these tests. To master the art of making decisions in the presence of uncertainties, probabilistic description of soil properties and reliability-based design play vital roles. Historically, the observational method (sometimes referred to as the “learn-as-you-go-approach”), sprung from ideas by Karl Terzaghi and later formulated by Ralph Peck, has been used in projects where the uncertainties are large and difficult to assess. The design approach is still highly suitable for numerous situations and is defined in Eurocode 7 for geotechnical design. In paper I, the Eurocode definition of the observational method is discussed. This paper concluded that further work in the probabilistic description of soil properties is highly needed, and, by extension, reliability-based design should be used in conjunction with the observational method. Although great progress has been made in the field of reliability-based design during the past decade, few geotechnical engineers are familiar with probabilistic approaches to design. In papers II and III, aspects of probabilistic descriptions of soil properties and reliability-based design are discussed. The connection between performing qualitative investigations and potential design savings is discussed in paper III. In the paper, uncertainties are assessed for two sets of investigations, one consisting of more qualitative investigations and hence with less uncertainty. A simplified Bayesian updating technique, referred to as “the multivariate approach”, is used to cross-validate data to reduce the evaluated total uncertainty. Furthermore, reliability-based design was used to compare the two sets of investigations with the calculated penetration depth for a sheet-pile wall. The study is a great example of how a small amount of both time and money (in the pre-investigation phase) can potentially lead to greater savings in the final design.

    Download full text (pdf)
    Thesis
  • 7.
    Prästings, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Managing uncertainties in geotechnical parameters: From the perspective of Eurocode 72019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Geotechnical engineering is strongly associated with large uncertainties. Geotechnical site investigations are made only at discrete points and most of a soil volume is never tested. A major issue is therefore how to cost effectively reduce geotechnical uncertainties with respect to structural performance. Managing the geotechnical uncertainties is thus an important aspect of the design process. Guidance on this subject is given in the European design code for geotechnical design, Eurocode 7 (EN 1997), which advocates the use of the partial-factor method, with the added possibility to use the observational method if the uncertainties are large and difficult to assess.This thesis aims to highlight, develop and improve methods to assess the quality and value of geotechnical site investigations through reliability-based design. The thesis also discusses the limitations of the deterministic partial-factor method, according to its EN 1997 definition, and how to better harmonise this design methodology with the risk-based approach of reliability-based design. The main research contributions are: (1) a presented case study showing the importance of and potential gains with a robust framework for statistical evaluation of geotechnical parameters, (2) the discussion on the limitations of the partial-factor method in EN 1997, and (3) the discussion on how to harmonise the EN 1997 definition of the partial-factor method with the risk-based approach of reliability-based design.

    Download full text (pdf)
    Thesis_Anders Prästings_Kappa DIVA
  • 8.
    Prästings, Anders
    et al.
    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.
    Müller, Rasmus
    Tyréns AB.
    Multivariate approach in reliability-based design of a sheet pile wall2016In: Transportation Geotechnics, ISSN 2214-3912, Vol. 7, p. 1-12Article in journal (Refereed)
    Abstract [en]

    In light of a restricted budget, there is a need to stress on the potential savings in conducting qualitative geotechnical investigations. This paper presents a case study on how site investigation efforts can be linked to potential savings in designing a sheet pile wall in central Sweden. The uncertainty in the undrained shear strength is a measure of investigation effort and have been evaluated from multivariate information, several investigation methods. A multivariate analysis (MVA) procedure based on Bayesian statistics was used to cross-validate information obtained by different investigation methods, thus allowing the uncertainty or effort to be updated (reduced) when additional investigations are included in the analysis. The uncertainty was evaluated for two sets of investigations, one of which included additional measurements and hence less uncertainty. A reliability-based design method, FOSM, was then used to study how the additional investigations affected the evaluated uncertainty and one design constraint of the sheet pile wall, namely the depth of penetration. The results show that the depth of penetration can potentially be reduced by approximately 11% of the total wall area.

  • 9.
    Prästings, Anders
    et al.
    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.
    Müller, Rasmus
    Tyréns AB.
    Optimizing geotechnical site-investigations2017In: Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017, 2017, p. 639-642Conference paper (Refereed)
    Abstract [en]

    One major question to deal with in the process of updating the current version of Eurocode 7 is how to convert thequality of a performed site-investigation into a measurable context. This should, in turn, affect the safety factor applied to the soil-strength properties in a limit state. This paper presents a study in which the total uncertainty from the evaluation of undrained shearstrength in clay is assessed from single and multiple site-investigation methods with regard to both random and systematicuncertainties. A Bayesian procedure is used to convert potential reduction of random and systematic uncertainties into a measurablecontext in relation to: (1) the type of site-investigation method, (2) the combination of methods, and (3) the number of measurementsperformed.

  • 10.
    Prästings, Anders
    et al.
    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.
    Müller, Rasmus
    Tyréns .
    Sannolik besparing av spont2016In: Bygg & teknik, ISSN 0281-658X, no 1, p. 47-51Article in journal (Other (popular science, discussion, etc.))
  • 11.
    Prästings, Anders
    et al.
    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.
    Müller, Rasmus
    Tyréns.
    Utvärdering av osäkerheter i geotekniska parametrar2014Conference paper (Other academic)
  • 12.
    Prästings, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Müller, Rasmus
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    The observational method applied to a high embankment founded on sulphide clay2014In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 181, p. 112-123Article in journal (Refereed)
    Abstract [en]

    Since its introduction, Eurocode 7 has acknowledged the observational method as a valid design approach for geotechnical structures. The observational method is defined in five paragraphs. Although several case studies have concluded that the observational method is useful, the method is still sparsely used. This study compares the actual implementation of the observational method in the Veda embankment project according to the definitions given in Eurocode 7. The outcome of the observational method as a design approach, and the major deviations compared to the definitions in Eurocode 7 are discussed. It is concluded that the design of a multi-staged embankment, where the building process is governed by consolidation in the subsoil, can only partly be adapted to the observational method as defined in Eurocode 7. Furthermore, when this is the case, the possibility of combining "design by calculations" and the observational method is discussed.

  • 13.
    Prästings, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Characteristic values of geotechnical parameters in Eurocode 72019In: Proceedings of the Institution of Civil Engeneers: Geotechnical Engineering, ISSN 1353-2618, E-ISSN 1751-8563, Vol. 172, no 4, p. 301-311Article in journal (Refereed)
    Abstract [en]

    Lack of harmonisation between reliability-based design and the partial factor method in Eurocode 7 (EN 1997-1:2004) is preventing the widespread introduction of a risk-based concept in geotechnical design. This paper discusses how uncertainties are managed according to EN 1997-1:2004 and possible implications of not harmonising the current safety format with reliability-based design. One of several challenges highlighted is how EN 1997-1:2004 defines the characteristic value and design value. The characteristic value is therein defined based on a classical frequentist approach through a confidence interval. From a Bayesian point of view, the current definition does not treat the characteristic value as an uncertain variable. Consequently, the definitions of the characteristic value and design value in EN 1997-1:2004 feature weak connections between uncertainties in the geotechnical properties and the consequences of failure, as regulated by the target reliability index.

  • 14.
    Prästings, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Müller, Rasmus
    Tyréns AB.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Bjureland, William
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Implementing the Extended Multivariate Approach in Design with Partial Factors for a Retaining Wall in Clay2017In: ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering, ISSN 2376-7642, Vol. 3, no 4, article id 04017015Article in journal (Refereed)
    Abstract [en]

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

  • 15.
    Spross, Johan
    et al.
    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.
    Probabilistic evaluation of settlement monitoring with the observational method during construction of embankments on clay2019In: Proceedings of the 7th International Symposium on Geotechnical Safety and Risk (ISGSR 2019): State-of-the-Practice in Geotechnical Safety and Risk / [ed] Jianye Ching, Dian-Qing Li and Jie Zhang, 2019, article id IS3-3Conference paper (Refereed)
    Abstract [en]

    Preloading  is  commonly  used  to  accelerate  primary  consolidation  and  increase  strength  under  embankments founded on highly compressible clay. By installing prefabricated vertical drains, this process can be even further accelerated. Because of significant geotechnical uncertainties, primarily regarding the vertical and horizontal coefficients of consolidation, prediction of settlement development with time is difficult. This paper shows how Bayesian statistics can be used to update a prior prediction of  the  final  settlement  from  the design  stage, with observations of  settlement made during  the preloading. With  this  approach,  the  observations  during  construction  are  used  to  significantly  reduce  the  considerable  epistemic uncertainty present at the design stage. This allows the surcharge design to be adjusted to suit the actual ground conditions, which is done by increasing the surcharge height if the settlement develops too slowly.

  • 16.
    Sölve, Hov
    et al.
    GeoMind.
    Persson, Erik
    Bjerking.
    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.
    Korrelationer mellan odräneradskjuvhållfasthet och förkonsolideringstryck i lera2018In: Bygg & teknik, ISSN 0281-658X, no 1, p. 55-58Article in journal (Other academic)
1 - 16 of 16
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