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Reducing uplift pressure uncertainty with measurements under concrete dams
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-5372-7519
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0002-8152-6092
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-9615-4861
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. 2551-2560 p.
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-136565ISBN: 978-1-884575-63-1 (print)OAI: oai:DiVA.org:kth-136565DiVA: diva2:676409
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
In thesis
1. A Critical Review of the Observational Method
Open this publication in new window or tab >>A Critical Review of the Observational Method
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
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:nbn:se:kth:diva-144207 (URN)
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

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Spross, JohanJohansson, FredrikLarsson, Stefan

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