Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
A Critical Review of the Observational Method
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-5372-7519
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Building a sustainable structure in soil or rock that satisfies all predefined technical requirements implies choosing a rational and effective construction method. An important aspect is how the performance of the structure is verified. For cases when the geotechnical behaviour is hard to predict, the existing design code for geotechnical structures, Eurocode 7, suggests the so-called “observational method” to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during construction, in order to accommodate the actual ground conditions, if the current design is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare. It is therefore not clear which prerequisites and circumstances that must be present for the observational method to be applicable and be the more suitable method.

This licentiate thesis gives a critical review of the observational method, based on, and therefore limited by, the outcome of the performed case studies. The aim is to identify and highlight the crucial aspects that make the observational method difficult to apply, thereby providing a basis for research towards a more applicable definition of the method. The main topics of discussion are (1) the apparent contradiction between the preference for advanced probabilistic calculation methods to solve complex design problems and sound, qualitative engineering judgement, (2) the limitations of measurement data in assessing the safety of a structure, (3) the fact that currently, no safety margin is required for the completed structure when the observational method is applied, and (4) the rigidity of the current definition of the observational method and the implications of deviations from its principles.

Based on the review, it is argued that the observational method can be improved by linking it to a probabilistic framework. To be applicable, the method should be supported by guidelines that explain and exemplify how to make the best use of it. The engineering judgement is however not lost; no matter how elaborate probabilistic methods are used, sound judgement is still needed to define the problem correctly. How to define such a probabilistic framework is an urgent topic for future research, because this also addresses the concerns regarding safety that is raised in the other topics of discussion.

Abstract [sv]

För att i berg eller jord kunna konstruera en anläggning, som uppfyller satta tekniska krav, krävs det att man väljer en rationell och effektiv konstruktionsmetod. En viktig aspekt i detta val är hur man verifierar konstruktionens funktion avseende exempelvis bärförmåga eller stadga. För fall när konstruktionens beteende svårt att förutsäga, erbjuder gällande standard (Eurokod 7) den så kallade observationsmetoden. Denna metod tillåter i förväg förberedda förändringar i designen under konstruktionstiden, om observationer av konstruktionens beteende indikerar att så behövs. På så vis anpassas konstruktionen till de faktiska förhållandena i marken. Trots att detta tillvägagångssätt i teorin borde ge en rationell design, används metoden sällan. Det råder därför oklarheter om vilka förutsättningar och omständigheter som krävs för att observationsmetoden ska kunna användas och dessutom utgöra den bästa lösningen.

I denna licentiatuppsats granskas observationsmetoden och dess användbarhet. Målet med licentiatuppsatsen är att belysa de aspekter som kan utgöra svårigheter när observationsmetoden används. Dessa identifierades under arbetet med några fallstudier. Licentiatuppsatsen ger därmed en utgångspunkt för fortsatt forskning för att ta fram en mer användbar definition av observationsmetoden. De viktigaste aspekterna som diskuteras i uppsatsen är (1) den skenbara motsatsen mellan användandet av sannolikhetsbaserade beräkningsmetoder för att lösa komplexa dimensioneringsfrågor och kvalitativa ingenjörsmässiga bedömningar, (2) de begränsningar som finns när man använder mätdata för att utvärdera konstruktioners säkerhet, (3) att det för tillfället saknas krav på säkerhetsmarginal mot brott för konstruktioner som byggts med observationsmetoden, och (4) vad svårigheten att uppfylla Eurokodens strikta definition innebär för metodens användbarhet.

Utifrån resultatet av granskningen dras slutsatsen att observationsmetoden kan förbättras genom att ge den ett sannolikhetsbaserat ramverk. För att förenkla användningen bör riktlinjer och anvisningar utformas. Även om metoden utvecklas mot en högre grad av beräkningskomplexitet, kommer ingenjörsmässiga bedömningar också framgent att vara viktiga, eftersom en avgörande aspekt är hur problemställningen formuleras. Med ett sannolikhetsbaserat ramverk ökar möjligheten att lösa de frågeställningar kring säkerhet som också diskuteras i uppsatsen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xii, 45 p.
Series
TRITA-JOB. LIC, ISSN 1650-951X ; 2024
Keyword [en]
Rock mechanics, observational method, Eurocode 7, reliability analysis, dam safety, tunnelling, system reliability
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-144207OAI: oai:DiVA.org:kth-144207DiVA: diva2:712427
Presentation
2014-05-07, B1, Brinellvägen 23, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20140415

Available from: 2014-04-15 Created: 2014-04-14 Last updated: 2014-04-15Bibliographically approved
List of papers
1. On the observational method for groundwater control in the Northern Link tunnel project, Stockholm, Sweden
Open this publication in new window or tab >>On the observational method for groundwater control in the Northern Link tunnel project, Stockholm, Sweden
2014 (English)In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 73, no 2, 401-408 p.Article in journal (Refereed) Published
Abstract [en]

For tunnelling in rock in Sweden, the public authorities usually set stringent requirements on low groundwater inflow to the tunnel, to minimise the risk of building settlement and the environmental impact. To improve this groundwater control, the potential application of the observational method in this matter was studied. A comparison was made between the actual implementation of groundwater control in the Northern Link road tunnel project in Stockholm and the definition of the observational method in Eurocode 7. The results showed that the groundwater control in the Northern Link project mainly agreed with the Eurocode. The significance of the deviations was discussed, and it was concluded that adopting the observational method for groundwater control so that it complied with Eurocode 7 would mostly entail simply a formalisation of today's procedures.

Keyword
Eurocode 7, Groundwater, Observational method, Tunnelling
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-136378 (URN)10.1007/s10064-013-0501-8 (DOI)000335156900011 ()2-s2.0-84899647565 (Scopus ID)
Funder
Formas
Note

QC 20140604

Available from: 2013-12-04 Created: 2013-12-04 Last updated: 2017-12-06Bibliographically approved
2. Reducing uplift pressure uncertainty with measurements under concrete dams
Open this publication in new window or tab >>Reducing uplift pressure uncertainty with measurements under concrete dams
2013 (English)In: Proceedings ICOLD 2013 International Symposium, Denver: US Society on Dams , 2013, 2551-2560 p.Conference paper, Published paper (Refereed)
Abstract [en]

In quantitative risk analyses of concrete dams founded on rock, it is necessary to consider the uplift pressure in the foundation with respect to both mean value and variation. With a more accurately predicted uplift pressure, the calculated probability of failure of the dam can be reduced. This paper proposes a methodology for predicting the current uplift pressure and related uncertainty, based both on pore pressure measurements and on expert judgment. An illustrative example is presented and the suggested methodology is compared with other conceivable approaches. The results are found to be reasonable in most conditions. However, it should be recognized that in risk analyses of dams, more extreme load cases not captured by the measurements also must be considered.

Place, publisher, year, edition, pages
Denver: US Society on Dams, 2013
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-136565 (URN)978-1-884575-63-1 (ISBN)
Conference
ICOLD 2013 International Symposium, Seattle, Washington. Denver: US Society on Dams
Note

QC 20140415

Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2014-04-15Bibliographically approved
3. On the use of pore pressure measurements in safety reassessments of concrete dams founded on rock
Open this publication in new window or tab >>On the use of pore pressure measurements in safety reassessments of concrete dams founded on rock
2013 (English)In: Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, ISSN 1749-9518, E-ISSN 1749-9526, Vol. 8, no 2, 117-128 p.Article in journal (Refereed) Published
Abstract [en]

In probabilistic stability analyses of concrete dams founded on rock, the uplift pressure is often a parameter of major importance. In previous literature, it has been suggested that assessing uplift with pore pressure measurements, instead of using empirical assumptions, could improve the calculated dam safety. This paper presents a coherent methodology to investigate whether incorporating pore pressure measurements has any impact on the calculated dam safety, based on Bayesian linear regression of pore pressure data in combination with series-system and the first-order reliability method. The study concludes that the probability of sliding failure is closely related to the probability of an extreme increase in uplift. Hence, measured uplift should only be incorporated while this probability remains sufficiently small, which requires proper programs both for uplift monitoring and for maintenance of drains and grout curtains.

Place, publisher, year, edition, pages
Taylor & Francis, 2013
Keyword
dam safety, dams, probability of failure, reliability analysis, system reliability
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-136377 (URN)10.1080/17499518.2013.864172 (DOI)2-s2.0-84897054569 (Scopus ID)
Note

QC 20140415

Available from: 2013-12-04 Created: 2013-12-04 Last updated: 2017-12-06Bibliographically approved
4. Towards an improved observational method
Open this publication in new window or tab >>Towards an improved observational method
2014 (English)In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium, Taylor & Francis Group, 2014, 1435-1440 p.Conference paper, Published paper (Refereed)
Abstract [en]

The observational method is today an accepted method in Eurocode 7 for design of geotechnical structures. However, case studies with formal application of its principles are still rare. One reason could be that the method to some extent is considered complex and associated with low safety margins. In fact, the Eurocode does not give any reference to how the safety of the completed structure can be assured. This paper strives to open up a discussion on how the observational method can be improved by including a requirement for a safety margin of the completed structure. A methodology is outlined and illustrated with a simple calculation example analysing the safety of a square rock pillar. Lastly, the compatibility with the observational method is discussed.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2014
Keyword
Rock mechanics, observational method, Eurocode, reliability-based design
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-144206 (URN)10.1201/b16955-250 (DOI)000345985300233 ()2-s2.0-84901325558 (Scopus ID)978-1-138-00149-7 (ISBN)
Conference
2014 ISRM European Regional Symposium on Rock Engineering and Rock Mechanics: Structures in and on Rock Masses, EUROCK 2014, Vigo, Spain, 26 May 2014 through 28 May 2014
Note

QC 20150108. Updated from manuscript to proceedings paper

Available from: 2014-04-14 Created: 2014-04-14 Last updated: 2016-09-23Bibliographically approved

Open Access in DiVA

spross_lic_kappa(542 kB)887 downloads
File information
File name FULLTEXT01.pdfFile size 542 kBChecksum SHA-512
682ca0d7f5c0fe66b7e333a6785c7d89b4f8c32a9d1899b4cc9fd05fd7afade61d378457627f7bbbdadc0aaf3c3c958662049609d7eb5e3d74a886bc65071dba
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Spross, Johan
By organisation
Soil and Rock Mechanics
Geotechnical Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 887 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 1136 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf