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Aspects on probabilistic approach to design: From uncertainties in pre-investigation to final design
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-5243-4650
2016 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , xiv, 38 p.
Series
TRITA-JOB. LIC, ISSN 1650-951X ; 2029
Keyword [en]
Reliability-based design, Geotechnical design, Geotechnical structures, Sheet-pile wall, Characterization of uncertainties, Geotechnical investigations
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-178088OAI: oai:DiVA.org:kth-178088DiVA: diva2:897119
Presentation
2016-02-26, V33, Teknikringen 72 (floor 5), KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
TRUST, Transparent Underground Structures
Funder
Swedish Research Council Formas
Note

QC 20160201

Available from: 2016-02-01 Created: 2015-12-07 Last updated: 2016-02-01Bibliographically 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, 112-123 p.Article 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.

Keyword
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: 2017-12-05Bibliographically 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, 1-15 p.Article 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: 2017-12-04Bibliographically approved
3. Multivariate approach in reliability-based design of a sheet pile wall
Open this publication in new window or tab >>Multivariate approach in reliability-based design of a sheet pile wall
2016 (English)In: Transportation Geotechnics, ISSN 2214-3912, Vol. 7, 1-12 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Geotechnical engineering, Geotechnical investigation, Multivariate analysis, Probabilistic design, Sheet pile wall
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-178083 (URN)10.1016/j.trgeo.2016.03.001 (DOI)000377794500001 ()2-s2.0-84962160879 (Scopus ID)
Note

QC 20160516

Available from: 2015-12-07 Created: 2015-12-07 Last updated: 2016-07-19Bibliographically approved

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Prästings, Anders

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