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Managing uncertainties in geotechnical parameters: From the perspective of Eurocode 7
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-5243-4650
2019 (English)Doctoral 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.

Abstract [sv]

Geoteknik förknippas med ett stort antal osäkerheter. Geotekniska undersökningar utförs i diskreta punkter och den absolut största delen av en jordvolym testas aldrig. En viktig fråga inom geotekniken är därför hur man kan minimera osäkerheterna i relation till kostnaderna för undersökningarna och konstruktionens säkerhet. En annan fråga som uppstår när en konstruktion ska dimensioneras är hur osäkerheterna bör hanteras i dimensioneringsprocessen. För detta ges vägledning i de europeiska dimensioneringsprinciperna för geotekniska konstruktioner, Eurokod 7 (EN 1997), som förespråkar partialkoefficientmetoden. Om osäkerheterna är stora och svåra att uppskatta kan observationsmetoden användas som ett komplement. Syftet med denna avhandling är att belysa, utveckla och förbättra metoder för bygg- och anläggningsbranschen att uppskatta kvalité och värde av geotekniska undersökningar. Ett bayesianskt tillvägagångssätt (multivariabel analys) har använts för att utvärdera osäkerheterna relaterade till de geotekniska undersökningarna. Därtill presenterar avhandlingen en diskussion om begränsningarna i partialkoefficientmetoden, enligt definitionen i EN 1997, och hur denna metod kan utvecklas för att bättre harmonisera med sannolikhetsbaserad dimensionering. De huvudsakliga forskningsbidragen är: (1) den presenterade fallstudien som visar vikten, och den potentiella nyttan, av ett robust ramverk för statistisk utvärdering av geotekniska parametrar som grund för sannolikhetsbaserad dimensionering, (2) diskussionen om begränsningarna med partialkoefficientmetoden enligt definitionen i EN1997, och (3) diskussionen om hur partialkoefficientmetoden kan utvecklas för att bättre harmonisera med sannolikhetsbaserad dimensionering.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 79
Series
TRITA-ABE-DLT ; 1924
Keywords [en]
Eurocode 7, Characteristic value, Partial-factor method, Reliability-based design
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-256058ISBN: 978-91-7873-249-4 (print)OAI: oai:DiVA.org:kth-256058DiVA, id: diva2:1344017
Public defence
2019-09-19, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council FormasSwedish Transport Administration
Note

QC 20190822

Available from: 2019-08-22 Created: 2019-08-20 Last updated: 2019-08-22Bibliographically approved
List of papers
1. The observational method applied to a high embankment founded on sulphide clay
Open this publication in new window or tab >>The observational method applied to a high embankment founded on sulphide clay
2014 (English)In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 181, p. 112-123Article in journal (Refereed) Published
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.

Keywords
Geotechnical engineering, Observational method, Eurocode 7, Embankments, Field testing and monitoring
National Category
Geology
Identifiers
urn:nbn:se:kth:diva-157215 (URN)10.1016/j.enggeo.2014.07.003 (DOI)000344426900010 ()2-s2.0-84908702194 (Scopus ID)
Note

QC 20141209

Available from: 2014-12-09 Created: 2014-12-08 Last updated: 2019-08-20Bibliographically approved
2. Comparison of geotechnical uncertainties linked to different soil characterization methods
Open this publication in new window or tab >>Comparison of geotechnical uncertainties linked to different soil characterization methods
2016 (English)In: Geomechanics and Geoengineering, ISSN 1748-6025, E-ISSN 1748-6033, p. 1-15Article in journal (Refereed) Epub ahead of print
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.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-161340 (URN)10.1080/17486025.2016.1184761 (DOI)2-s2.0-84969753258 (Scopus ID)
Note

QC 20160608

Available from: 2015-03-11 Created: 2015-03-11 Last updated: 2019-08-20Bibliographically approved
3. On empirical correlations for normalised shear strengths from fall cone and direct simple shear tests in soft Swedish clays
Open this publication in new window or tab >>On empirical correlations for normalised shear strengths from fall cone and direct simple shear tests in soft Swedish clays
2019 (English)In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529Article in journal (Refereed) Submitted
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-256056 (URN)
Note

QC 20190823

Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2019-08-23Bibliographically approved
4. Implementing the Extended Multivariate Approach in Design with Partial Factors for a Retaining Wall in Clay
Open this publication in new window or tab >>Implementing the Extended Multivariate Approach in Design with Partial Factors for a Retaining Wall in Clay
Show others...
2017 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2017
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-211541 (URN)10.1061/AJRUA6.0000918 (DOI)000423145500009 ()2-s2.0-85045346080 (Scopus ID)
Funder
Swedish Transport AdministrationSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning
Note

QC 20170808

Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2019-08-20Bibliographically approved
5. Optimizing geotechnical site-investigations
Open this publication in new window or tab >>Optimizing geotechnical site-investigations
2017 (English)In: Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017, 2017, p. 639-642Conference paper, Published 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.

Abstract [fr]

L’une des questions majeures qui se posent lors du processus de mise à jour de la version actuelle de l’Eurocode 7est la suivante : comment convertir la qualité d’une investigation de site en une quantité mesurable ? Cela devrait alors affecterle niveau de sécurité appliqué aux propriétés de résistance du sol dans un état limite. Cet article présente une étude au cours de laquelle l’incertitude totale découlant de l’évaluation de la résistance au cisaillement de l’argile non évacuée est évaluée à partir de méthodes d’investigation de site uniques et multiples en relation avec des incertitudes aléatoires et systématiques. Une procédure bayésienne est utilisée pour convertir la réduction potentielle des incertitudes aléatoires et systématiques en une incertitude mesurable en rapport avec : (1) le type de méthode d’investigation de site, (2) la combinaison des méthodes, (3) le nombre de mesures effectuées.

National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-221082 (URN)2-s2.0-85040043034 (Scopus ID)
Conference
19th International Conference on Soil Mechanics and Geotechnical Engineering, 17 to 21 September 2017, Seoul 2017
Funder
Swedish Research Council Formas
Note

QC 20180115

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2019-08-20Bibliographically approved
6. Characteristic values of geotechnical parameters in Eurocode 7
Open this publication in new window or tab >>Characteristic values of geotechnical parameters in Eurocode 7
2019 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
ICE Publishing, 2019
Keywords
codes of practice & standards, geotechnical engineering, risk & probability analysis
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-255551 (URN)10.1680/jgeen.18.00057 (DOI)000475709400002 ()2-s2.0-85068838228 (Scopus ID)
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-20Bibliographically approved

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