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| 2. |
- Bjureland, William, et al.
(författare)
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Reliability aspects of rock tunnel design with the observational method
- 2017
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1365-1609 .- 1873-4545. ; 98, s. 102-110
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Hov, Sölve, et al.
(författare)
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On Empirical Correlations for Normalised Shear Strengthsfrom Fall Cone and Direct Simple Shear Tests in SoftSwedish Clays
- 2021
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Ingår i: Geotechnical and Geological Engineering. - : Springer Nature. - 0960-3182 .- 1573-1529. ; 39:7, s. 4843-4854
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Tidskriftsartikel (refereegranskat)abstract
- Empirical correlations provide valuable information in early design stages, and they help tovalidate or discard single values from site investigations.This paper presents a multivariate database from commercial projects consisting of evaluated shear strengths obtained from direct simple shear tests and fall cone tests (which are calibrated to the field vane test), including index tests. The multivariate databaseis used to investigate the performance of common transformation models and to test the recommended correction for fall cone tests. It is found that the measured normalised shear strength evaluated from direct simple shear tests and fall cone tests is correlated to the liquid limit and that the results conform to Swedish and Norwegian recommendations. However, the scatter is large, more for fall cone tests than for direct simple shear tests, which is thought to depend mainly on sample disturbance. It can however be concluded that the trend of normalised shear strengths increases with increasing plasticity.
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| 4. |
- Prästings, Anders, 1984-
(författare)
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Aspects on probabilistic approach to design : From uncertainties in pre-investigation to final design
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Prästings, Anders, 1984-, et al.
(författare)
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Characteristic values of geotechnical parameters in Eurocode 7
- 2019
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Ingår i: Proceedings of the Institution of Civil Engeneers. - : ICE Publishing. - 1353-2618 .- 1751-8563. ; 172:4, s. 301-311
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Prästings, Anders, 1984-, et al.
(författare)
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Erratum: : Implementing the Extended Multivariate Approach in Design with Partial Factors for a Retaining Wall in Clay" by Anders Prästings, Johan Spross, Rasmus Müller, Stefan Larsson, William Bjureland, and Fredrik Johansson (ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering (1983) (257–277) DOI; 10.1061/AJRUA6.0000918)
- 2017
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Ingår i: ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering. - : American Society of Civil Engineers (ASCE). - 2376-7642. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- Several corrections should be made to the original paper. The errors include corrections to Eqs. (8) and (9). Furthermore, a mistake in the calculation of the uncertainty related to random measurement error, COVe;Di , requires corrections to Table 4 and to Figs. 7, 9, and 10. The corrections of the calculation results are inconsequential and do not alter the conclusions of the published paper. The corrections are given subsequently.Corrections to Section “Project Description and Site Characterization” [Eqs. (8a), (8b), and (9)] In Eqs. (8) and (9), the braces defining the measured or evaluated property, δi, and transformation factor, Ci, are incorrectly stated. The correct equations are provided as follows: (Formula Presented) (Table Presented) Thus, when α varies between 1.0 and 0.6, γM=η ranges from 1.16 to 1.29.
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| 7. |
- Prästings, Anders, 1984-, et al.
(författare)
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Optimizing geotechnical site-investigations
- 2017
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Ingår i: Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017. ; , s. 639-642
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Konferensbidrag (refereegranskat)abstract
- 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.
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