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Excavation damage from blasting with emulsion explosives: Quality control and macro fracturing in the remaining rock
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Svensk Kärnbränslehantering AB.
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Excavation damage is usually regulated in Swedish infrastructure tunnel contracts as it can influence the quality and lifecycle cost for tunneling projects. The topic is important for underground constructions with a long operation period such as tunnels for public transport, permanent access tunnels in mines or underground repositories for nuclear waste. In competent crystalline rock, excavation damage is often simplified to macro fractures induced by blasting as this has the most significant impact on the remaining rock. Blasting in Scandinavian tunneling projects is mostly conducted with pumpable emulsion explosives and a good result is often dependent on control of the charging process, i.e. that the explosives are charged according to the blast design.

This thesis is based on data from five field investigations carried out in Sweden and Finland. In addition, data from a case study on quality control and documentation in a tunnel excavation project in Äspö Hard Rock Laboratory (HRL) is also included. Data on blast fracture length and frequency have been compiled from all sites, where emulsion explosives were used. The sites include experimental tunnels, a road tunnel, an underground depot for subway trains and a wastewater tunnel. Data from the field investigations have been analyzed using statistical methods including statistical hypothesis test and multivariate data analysis by means of Principal Component Analysis (PCA).

The evaluation method gives indications as to how blast design and geology influence the development of blast fractures. Charge concentration was found to be the most influential design variable and simultaneous initiation of contour holes (delay time <1 ms) gave shorter blast fractures with a longest blast fracture of approx. 25 cm compared to approx. 40 cm from pyrotechnical initiation. However, the delay time had limited influence on the number of blast fractures in the remaining rock. Results from the PCA suggest that blast fractures length could be dependent also on geology.

Three main groups of fracture patterns were identified, one group with relatively few and short fractures, a group with several longer blast fractures and a group with few or a single long blast fracture. The result shows differences in fracture length between the column and bottom charge part of the contour holes, with blast fracture lengths up to approx. 40 cm for the column charge and up to approx. 60 cm for the bottom charge.

The case study showed that good precision in charging with string emulsion can be achieved and documented using modern logger technology in drilling and charging equipment. However, the methods applied for evaluation of charging precision as well as documentation require manual processing and interpretation of data. Further development of the logger systems and processing software is needed in order to follow up logged amounts of emulsion explosive during production.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Geotechnical Engineering
Research subject
Mining and Rock Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-67456ISBN: 978-91-7790-047-4 (print)ISBN: 978-91-7790-048-1 (electronic)OAI: oai:DiVA.org:ltu-67456DiVA, id: diva2:1179603
Presentation
2018-02-28, F1031, Luleå Tekniska Universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
Rock Engineering Research Foundation (BeFo)Available from: 2018-02-02 Created: 2018-02-01 Last updated: 2018-03-02Bibliographically approved
List of papers
1. Design and control of the EDZ for a deep repository in crystalline rock
Open this publication in new window or tab >>Design and control of the EDZ for a deep repository in crystalline rock
2014 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

Knowledge about the Excavation Damaged Zone (EDZ) is essential for underground construction design, underground facility layout, work environment issues and analysis of post-closure safety for a final repository for nuclear waste. The EDZ is defined as the zone around a tunnel where the damage is not reversible. The EDZ can be caused by the excavation method as well as by the actual strength–stress conditions.SKB has chosen the Forsmark site for disposal of spent fuel. The site conditions include hard crystalline rock and fairly high stresses. However, analyzes prior to site selection found that the risk for stress induced development of an EDZ is limited. The aim of this paper is to outline the blast design concept and quality control measures to ensure that the excavation method fulfills the requirements. Strategies for blast design and QA/QC measures for tunnel excavation were applied during construction works for the Äspö HRL expansion 2012. This provided an opportunity to demonstrate methods for tunnel excavation and verify that requirements on minimizing the EDZ could be met during the construction of the planned Swedish final repository for spent fuel.

National Category
Other Civil Engineering
Identifiers
urn:nbn:se:ltu:diva-37287 (URN)b43aa003-de4a-430f-8b57-9e49df2c35f2 (Local ID)b43aa003-de4a-430f-8b57-9e49df2c35f2 (Archive number)b43aa003-de4a-430f-8b57-9e49df2c35f2 (OAI)
Conference
ISRM International Symposium EUROCK : 26/05/2014 - 28/05/2014
Note
Upprättat; 2014; 20160513 (henitt)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-02-01Bibliographically approved
2. Recent Swedish Studies on the Extent of Blast Damage after Excavation
Open this publication in new window or tab >>Recent Swedish Studies on the Extent of Blast Damage after Excavation
Show others...
2016 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

This paper presents two recent studies on the extent of blast damage after excavation in crystalline rock. The Swedish Transport Administration and the Swedish Nuclear Fuel and Waste Management Company (SKB) are both under regulations to limit excavation damage during construction of tunnels. SKB is also required to limit the Excavation Damage Zone (EDZ), as this could be a potential flow path for radionuclides in the planned repository for spent nuclear fuel.Presented in this paper are investigations of blast damage from three tunnel sites, a road tunnel, an experimental tunnel in Äspö Hard Rock Laboratory and an underground subway depot.As expected the fractures resulting from the bottom charge are both longer and more frequent then those mapped in the column charge. The results show that the requirement to limit blast damage according to Swedish regulations was fulfilled for the column charge at the three studied sites.

National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-39564 (URN)e60f1a29-4bed-4969-b2d3-a702d938deb5 (Local ID)e60f1a29-4bed-4969-b2d3-a702d938deb5 (Archive number)e60f1a29-4bed-4969-b2d3-a702d938deb5 (OAI)
Conference
World Tunnel Congress : 22/04/2016 - 28/04/2016
Note
Godkänd; 2016; 20160513 (henitt)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-04-16Bibliographically approved
3. Investigation of blast fractures from mechanized charging with emulsion during tunnelling
Open this publication in new window or tab >>Investigation of blast fractures from mechanized charging with emulsion during tunnelling
2017 (English)In: Proceedings of the World Tunnel Congress 2017: Surface challenges – Underground solutions, 2017, p. 1542-1549Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Aquality factor that can decrease the need for rock reinforcement andmaintenance in underground facilities is limitation of blast damage in thetunnel contour. This paper presents results from a project initiated by the SKBand Forcit Sweden AB to investigate the extent of blast damage from emulsionexplosives. The investigations were conducted at two tunnel sites in Sweden,Äspö HRL and a wastewater tunnel under construction in Kista. The tunnels wereexcavated with the same technology for mechanized charging but with differentpurposes and quality requirements. Results from the presented project includefracture mapping of the excavated slots, blast fracture length and frequency,calculated charge concentration for mapped blasting halfpipes in the slots atÄspö HRL and measurements of VOD (velocity of detonation) in the wastewatertunnel in Kista and the Kankberg mine.

National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-67455 (URN)
Conference
ITA-AITES World Tunnel Congress, Bergen, 9-15 June 2017
Funder
Rock Engineering Research Foundation (BeFo)
Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2018-02-12Bibliographically approved
4. Multivariate evaluation of blast damage from emulsion explosives in tunnels excavated in crystalline rock
Open this publication in new window or tab >>Multivariate evaluation of blast damage from emulsion explosives in tunnels excavated in crystalline rock
2019 (English)In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 85, p. 331-339Article in journal (Refereed) Published
Abstract [en]

Blast damage in tunnels is usually regulated in Swedish infrastructure contracts as it can influence the quality and lifecycle cost for tunneling projects. The topic is important for underground constructions with a long operation period such as tunnels for public transport, permanent access tunnels in mines or underground repositories for nuclear waste. This paper aims to evaluate the influence of design and geology variables on the resulting blast fracture length and frequency by means of multivariate data analysis. The analysis was based on data from five field investigations carried out at tunnel sites in Sweden and Finland where emulsion explosives were used. Data was compiled and analyzed using Principal Component Analysis (PCA). Charge concentration was found to be the most influential design variable and hole spacing had limited influence on blast fracturing. Results from the PCA suggest that blast fractures length could be dependent also on geology and natural fractures. Three main groups of fracture patterns were identified, one group with relatively few and short blast fractures, a group with several longer blast fractures and a group with few or a single long blast fracture. The result shows differences in fracture length between the column and bottom charge part of the contour holes, with blast fracture lengths up to approx. 40 cm for the column charge and up to approx. 60 cm for the bottom charge.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Blasting, Blast damage, Emulsion explosives, Mechanized charging, Principal Component Analysis
National Category
Geotechnical Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-67454 (URN)10.1016/j.tust.2018.12.021 (DOI)000457512000031 ()2-s2.0-85059473074 (Scopus ID)
Funder
Rock Engineering Research Foundation (BeFo)
Note

Validerad;2019;Nivå 2;2019-01-10 (svasva)

Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2019-04-23Bibliographically approved

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