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Shear strength of partially bonded concrete-rock interfaces for application in dam stability analyses
KTH, School of Architecture and the Built Environment (ABE).ORCID iD: 0000-0003-4555-0471
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
2016 (English)In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Refereed) Epub ahead of print
Abstract [en]

The shear strength of the concrete–rock interface has a substantial influence on the sliding stability of concrete gravity dams founded on rock. While several studies have been done on concrete–rock contacts, there remains uncertainty regarding the peak shear strength of partially bonded interfaces. There exists, in particular, an uncertainty regarding the contribution from surface roughness of the unbonded parts to the peak shear strength of the interface due to the dependency of mobilized strength on shear displacement. In this study, a series of 24 direct shear tests are performed under CNL conditions on concrete–rock samples with different bonding conditions. Tests on samples with fully bonded and unbonded interfaces are conducted to study the strain compatibility of the different contacts, while the results of samples with partially bonded interfaces are evaluated in the context of linking the joint roughness of the unbonded parts to the peak shear strength of the interface. The results indicate that a significant part of the surface roughness of the unbonded parts is mobilized prior to degradation of bond strength, in particular for interfaces with low bonding percentages. It is recommended that further research should be conducted to understand how the contribution from roughness change with an increase in scale and degree of matedness.

Place, publisher, year, edition, pages
2016.
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-184115DOI: 10.1007/s00603-016-0962-8ISI: 000379015700013ScopusID: 2-s2.0-84962169543OAI: oai:DiVA.org:kth-184115DiVA: diva2:914866
Note

QC 20160516

Available from: 2016-03-27 Created: 2016-03-27 Last updated: 2016-08-15Bibliographically approved
In thesis
1. Sliding stability re-assessment of concrete dams with bonded concrete-rock interfaces
Open this publication in new window or tab >>Sliding stability re-assessment of concrete dams with bonded concrete-rock interfaces
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The shear strength of the concrete-rock interface is an important parameter in sliding stability analyses of concrete dams founded on rock and depends, in addition to the normal stress state, on the bonding conditions of the interface; concrete-rock interfaces can be either unbonded, partially bonded or fully bonded.

In the Swedish guidelines for dam safety all dam-foundation contacts are treated as unbonded. This has the benefit of eliminating all uncertainties related to the cohesive strength of bonded contacts but it might also lead to unnecessary strengthening of dams. Other national guidelines deal with the uncertainties related to cohesion by applying higher safety factors, mainly determined based on previous experience, when both cohesion and friction are taken into account.

The main objective of this project is to study if and how cohesion can be included when evaluating the shear strength of bonded or partially bonded interfaces. To accomplish this, uncertainties associated with cohesion are identified and their influence on the assessed stability is investigated.

The results show that the influence on the assessed sliding stability is strongly dependent on the magnitude of the involved uncertainties that might vary significantly for different dams. It is thus questionable if one safety factor applicable for all dams can be established for use in deterministic analyses.

Taking into account cohesion when reliability methods are used is somewhat less complicated because of the possibility of directly incorporating the uncertainties in the analysis. The main challenge in such cases is the quantification of the involved uncertainties due to lack of proper data and, in some cases, knowledge. In this thesis, a framework for quantification of parameter uncertainty is suggested and the model error due to brittle failure in combination with spatial variation in cohesion is analysed. Areas that require more research to further refine the analysis are also identified.

Abstract [sv]

Skjuvhållfastheten i betong-berggränssnittet är en avgörande faktor vid glidstabilitetsutvärderingar av befintliga betongdammar grundlagda på berg och beror dels på normalspänningsfördelningen och dels på kontaktytans status med avseende på vidhäftning, vilken kan delas in i tre separata fall; då vidhäftning existerar och kohesion medräknas (intakt), då vidhäftning aldrig funnits eller förlorats (bruten), samt en kombination av föregående (delvis intakt).

I RIDAS, de svenska riktlinjerna för dammsäkerhet, behandlas alla berg-betonggränssnitt som brutna. Detta förhållningssätt har fördelen att det utelämnar all osäkerhet förknippad med intakta kontaktytors kohesion men det kan också resultera i icke nödvändiga förstärkningar av dammar. I andra nationella riktlinjer för dammsäkerhet beaktas osäkerheterna förknippade med kohesion genom att högre säkerhetsfaktorer, i huvudsak bestämda baserat på erfarenhet, tillämpas då både kohesion och friktion används vid beräkning av kontaktytans skjuvhållfasthet.

Det övergripande syftet med detta doktorandprojekt är att studera om och hur kohesion kan medräknas vid stabilitetsutvärderingar av befintliga betongdammar med helt eller delvis intakta betong-berggränssnitt. För att uppnå detta, identifieras osäkerheter förknippande med kohesionen och deras inverkan på den bedömda glidstabiliteten utvärderas.

Resultaten från projektet visar att osäkerheternas inverkan på den uppskattade glidstabiliteten är starkt beroende av osäkerheternas storlek, vilken varierar för olika dammar. Det är således tveksamt om en säkerhetsfaktor giltig för alla dammar kan bestämmas för användning i deterministiska stabilitetsanalyser. När sannolikhetsbaserade metoder används kan osäkerheterna införlivas direkt i analysen. Kvantifieringen av osäkerheterna förknippade med ett specifikt fall utgör då den huvudsakliga utmaningen. I denna avhandling presenteras ett ramverk för att uppskatta de statistiska parametrarna hos de ingående variablerna. Dessutom studeras modellosäkerheten förknippad med intakta gränssnitts spröda brott i kombination med kohesionens rumsliga variation i detalj. Områden som fordrar ytterligare forskning i syfte att förbättra analysen identifieras också.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. xxiv, 71 p.
Series
TRITA-JOB PHD, ISSN 1650-9501 ; 2031
Keyword
concrete dams, sliding stability, cohesion, shear strength, uncertainty, bond
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-185144 (URN)978-91-7595-907-8 (ISBN)
Public defence
2016-05-04, Kollegiesalen, Brinellvägen 8, KTH campus, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20160411

Available from: 2016-04-11 Created: 2016-04-11 Last updated: 2016-04-11Bibliographically approved

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Krounis, AlexandraJohansson, FredrikLarsson, Stefan
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