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Some aspect of reliability-based design for tunnels using observational method (EC7)
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
KTH, School of Architecture and the Built Environment (ABE).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.
2015 (English)In: EUROCK 2015 & 64th Geomechanics Colloquium, Salzburg, 2015Conference paper, Published paper (Refereed)
Abstract [en]

According to Eurocode 7, the observational method is an accepted design method, where a preliminary design may be updated as the construction progresses. However, Eurocode 7 does not give any advice on how to relate the observations to the acceptable level of safety of the structure. In this paper, we outline a methodology for how to use deformation measurements to predict the final deformation of a circular rock tunnel to calculate the probability of failure. Consequently, the measurements can be used to verify that the design does not violate the specified safety level. The paper shows the potential of combining the observational method with reliability-based design in tunneling

Place, publisher, year, edition, pages
Salzburg, 2015.
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-184132OAI: oai:DiVA.org:kth-184132DiVA: diva2:914949
Conference
ISRM Regional Symposium Eurock 2015
Note

QC 20160408

Available from: 2016-03-28 Created: 2016-03-28 Last updated: 2017-04-04Bibliographically approved
In thesis
1. Toward a reliability framework for the observational method
Open this publication in new window or tab >>Toward a reliability framework for the observational method
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Constructing sustainable structures in rock that satisfy all predefined technical specifications requires rational and effective construction methods. When the geotechnical behaviour is hard to predict, the Euro­pean design code, Eurocode 7, suggests application of the 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 to comply with 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.

Investigating the applicability of the observational method in rock en­gineering, the aim of this thesis is to identify, highlight, and solve the aspects of the method that limit its wider application. Furthermore, the thesis aims to improve the conceptual understanding of how design deci­sions should be made when large uncertainties are present.

The main research contribution is a probabilistic framework for the observational method. The suggested methodology allows comparison of the merits of the observational method with that of conventional design. Among other things, the thesis also discusses (1) the apparent contradiction between the preference for advanced probabilistic calculation methods and sound, qualitative engineering judgement, (2) how the establishment of limit states and alarm limits must be carefully considered to ensure structural safety, and (3) the applicability of the Eurocode defini­tion of the observational method and the implications of deviations from its principles.

Abstract [sv]

För att kunna konstruera en anläggning i berg, som uppfyller satta tek­niska krav, krävs det en rationell och effektiv konstruktionsmetod. När konstruktionens beteende är svårt att förutsäga, erbjuder den europeiska standarden 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 ger en rationell design, används metoden sällan i enlighet med Eurokod 7.

Denna doktorsavhandling undersöker tillämpbarheten av observa-tionsmetoden när man bygger i och på berg. Målet är att belysa de aspekter som begränsar dess användning och i dessa fall föreslå förbätt­ringar som ökar tillämpbarheten. I ett vidare perspektiv syftar avhand­lingen även till att förbättra den konceptuella förståelsen för hur beslut bör fattas i designprocessen när det finns stora osäkerheter.

Avhandlingen visar hur observationsmetoden kan användas i ett san­nolikhetsbaserat ramverk. Metodiken ger användaren möjlighet att jäm­föra för- och nackdelarna med observationsmetoden och konventionell dimensionering. Avhandlingen diskuterar bland annat även (1) den skenbara motsatsen mellan användandet av sannolikhetsbaserade beräkningsmetoder för att lösa komplexa dimensioneringsfrågor och kvalitativa ingenjörsmässiga bedömningar, (2) hur larmgränser och brottgränstillstånd bör definieras för att ge tillräcklig säkerhetsmarginal, samt (3) hur Eurokod 7:s strikta definition av observationsmetoden påverkar dess användbarhet.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2016
Series
TRITA-JOB PHD, ISSN 1650-9501 ; 1023
Keyword
Rock engineering, observational method, Eurocode 7, structural safety, reliability analysis, dam safety, Bergmekanik, observationsmetoden, Eurokod 7, sannolikhetsbaserad dimensionering, dammsäkerhet
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-192825 (URN)978-91-7729-128-2 (ISBN)
Public defence
2016-10-25, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160926

Available from: 2016-09-26 Created: 2016-09-20 Last updated: 2016-09-26Bibliographically approved
2. On reliability-based design of rock tunnel support
Open this publication in new window or tab >>On reliability-based design of rock tunnel support
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Tunneling involves large uncertainties. Since 2009, design of rock tunnels in European countries should be performed in accordance with the Eurocodes. The main principle in the Eurocodes is that it must be shown in all design situations that no relevant limit state is exceeded. This can be achieved with a number of different methods, where the most common one is design by calculation. To account for uncertainties in design, the Eurocode states that design by calculation should primarily be performed using limit state design methods, i.e. the partial factor method or reliability-based methods. The basic principle of the former is that it shall be assured that a structure’s resisting capacity is larger than the load acting on the structure, with high enough probability. Even if this might seem straightforward, the practical application of limit state design to rock tunnel support has only been studied to a limited extent.

The aim of this licentiate thesis is to provide a review of the practical applicability of using reliability-based methods and the partial factor method in design of rock tunnel support. The review and the following discussion are based on findings from the cases studied in the appended papers. The discussion focuses on the challenges of applying fixed partial factors, as suggested by Eurocode, in design of rock tunnel support and some of the practical difficulties the engineer is faced with when applying reliability-based methods to design rock tunnel support.

The main conclusions are that the partial factor method (as defined in Eurocode) is not suitable to use in design of rock tunnel support, but that reliability-based methods have the potential to account for uncertainties present in design, especially when used within the framework of the observational method. However, gathering of data for statistical quantification of input variables along with clarification of the necessary reliability levels and definition of “failure” are needed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 52 p.
Series
TRITA-JOB. LIC, ISSN 1650-951X ; 2033
Keyword
Rock engineering, reliability-based design, Eurocode 7, observational method, tunnel engineering, Bergmekanik, sannolikhetsbaserad dimensionering, Eurokod 7, observationsmetoden, tunnelbyggnation.
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-204919 (URN)978-91-7729-354-5 (ISBN)
Presentation
2017-05-18, B3, Brinellvägen 23, KTH-Campus, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20170407

Available from: 2017-04-07 Created: 2017-04-04 Last updated: 2017-04-07Bibliographically approved

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