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Analytical and numerical approaches to estimate peak shear strength of rock joints
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0002-8621-694X
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In Sweden, there exists a large number of dams. Many of them are founded on rock masses normally affected by the presence of sub-horizontal rock fractures, which makes sliding along rock joints under the dam foundation one of the most critical failure mechanism. Various attempts have been made to relate the peak shear strength of rock joints to measurable parameters. However, the uncertainty in the determination of the shear strength of rock joints is nonetheless still significant.The main aim of this thesis is to investigate, develop and apply analytical and numerical techniques for estimation of peak shear strength of natural and unfilled rock joints. In a first step, the peak shear strength of several natural and unfilled rock joint was calculated by using surface aperture measurements from high-resolution optical scanning and a modified version of the analytical criterion previously developed by Johansson and Stille in 2014. In a second step, PFC2D was utilised to perform numerical shear tests on two-dimensional profiles selected from high-resolution optical scanning on unweathered and perfectly mated tensile induced rock joints.The results from the analytical approach show that the calculated peak shear strengths of the analysed samples are in good agreement compared with the laboratory investigations. Conversely, the obtained results from the numerical approach show lower peak shear strengths in the analysed two-dimensional profiles compared with the conducted laboratory shear tests.The analytical approach together with the advanced techniques to measure surface roughness available today, may be a possible way forward towards a methodology to determine peak shear strength of large-scale natural rock joints in-situ.

Abstract [sv]

Bergsprickors skjuvhållfasthet är en avgörande faktor för att kunna bestämma säkerheten mot gliding för dammar där sub-horisontella utbredda bergsprickor existerar. Samtidigt är parametern svår att bestämma då den påverkas av flera faktorer som sprickytans råhet, vittringsgrad, normalspänning, skala samt passning. Skjuvhållfasthet av bergsprickor kan bestämmas genom att använda empiriska och analytiska brottkriterier samt numeriska metoder. Problemet med de befintliga metodikerna är att de inte beaktar inverkan från sprickans passning. Detta innebär att hållfastheten riskerar att överskattas.Det övergripande syftet med denna licentiatuppsats är att studera, utveckla och tillämpa analytiska och numeriska metoder för uppskattning av skjuvhållfasthet för naturliga och ofyllda bergsprickor. I ett första steg beräknades skjuvhållfastheten för ett antal naturliga och ofyllda bergsprickor. Detta gjordes genom att mäta aperturen baserat på högupplöst skanning och en vidareutvecklad version av det analytiska kriteriet som föreslogs av Johansson och Stille 2014. I ett andra steg användes PFC2D för att genomföra numeriska skjuvtester på två-dimensionella sprickprofiler baserat på högupplöst skanning av perfekt passade och draginducerade bergsprickor.Resultaten från uppskattad skjuvhållfasthet med den analytiska metodiken visar på en bra överensstämmelse i jämförelse med de utförda skjuvförsöken. Resultaten från de utförda analyserna med PFC2D visar på en något lägre skjuvhållfasthet än vad som observeras i verkligheten.Den utvecklade analytiska metodiken, tillsammans med de avancerade tekniker som idag finns för att mäta sprickytornas råhet, bedöms kunna utgöra ett första steg mot att bättre kunna bestämma den storskaliga skjuvhållfastheten för bergsprickor i fält.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 53
Series
TRITA-ABE-DLT ; 196
Keywords [en]
Rock joint, Shear strength, Failure criterion, Numerical shear tests
Keywords [sv]
Bergsprickor, Skjuvhållfasthet, Brottkriterium, Numeriska skjuvförsök
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-248019ISBN: 978-91-7873-150-3 (print)OAI: oai:DiVA.org:kth-248019DiVA, id: diva2:1301601
Presentation
2019-04-25, B3, Brinellvägen 23, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-03Bibliographically approved
List of papers
1. Peak shear strength of natural and unfilled rock joints based on measured average aperture
Open this publication in new window or tab >>Peak shear strength of natural and unfilled rock joints based on measured average aperture
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-248014 (URN)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-06-19Bibliographically approved
2. Comparison between shear strength of real and numerical shear tests on rock joints using PFC2D
Open this publication in new window or tab >>Comparison between shear strength of real and numerical shear tests on rock joints using PFC2D
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-248015 (URN)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-05-21Bibliographically approved
3. Comparison between shear strength based on Barton’s roughness profiles and equivalent synthetic profiles based on fractal theory
Open this publication in new window or tab >>Comparison between shear strength based on Barton’s roughness profiles and equivalent synthetic profiles based on fractal theory
2018 (English)In: 52nd U.S. Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association (ARMA) , 2018Conference paper, Published paper (Refereed)
Abstract [en]

A comprehensive understanding of the shear strength and the mechanical behavior of rock joints is to some extent still missing today. Several attempts have been made to develop empirical and analytical shear strength criteria that explain this mechanism. One of the most important parameters governing the shear strength of rock fractures is the surface roughness, which is generally determined using the Joint Roughness Coefficient (JRC). This parameter is often determined subjectively in the field by comparison with 10 predefined roughness profiles. Recent studies indicate that surface roughness can be accurately represented by using fractal analysis. The aim of this study is to perform a first attempt to investigate the mechanical equivalence in terms of the peak shear strength between synthetic rock fractures, where the surface roughness has been generated using fractal theory, and standard roughness profiles from Barton and Choubey, 1977, using the particle flow code PFC2D. The results from the numerical shear tests under constant normal load (CNL) are compared with the predicted peak shear strength using Barton’s criterion and a back-calculation of the JRC value is carried out.

Place, publisher, year, edition, pages
American Rock Mechanics Association (ARMA), 2018
Keywords
Fractals, Rock mechanics, Rocks, Shear flow, Back calculation, Fractal analysis, Fractal theory, Joint roughness coefficients, Mechanical behavior, Particle flow code, Peak shear strength, Strength criteria, Surface roughness
National Category
Geophysical Engineering
Identifiers
urn:nbn:se:kth:diva-236439 (URN)2-s2.0-85053478312 (Scopus ID)
Conference
52nd U.S. Rock Mechanics/Geomechanics Symposium, 17 June 2018 through 20 June 2018, Seattle, WA, USA
Note

QC 20181025

Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2019-04-16Bibliographically approved

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  • apa
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