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Investigation of blast fractures from mechanized charging with emulsion during tunnelling
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Svensk Kärnbränslehantering AB.
Forcit Sweden AB.
Forcit Sweden AB.
Forcit Norway AS.
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.

Place, publisher, year, edition, pages
2017. p. 1542-1549
National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-67455OAI: oai:DiVA.org:ltu-67455DiVA, id: diva2:1179597
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
In thesis
1. Excavation damage from blasting with emulsion explosives: Quality control and macro fracturing in the remaining rock
Open this publication in new window or tab >>Excavation damage from blasting with emulsion explosives: Quality control and macro fracturing in the remaining rock
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:nbn:se:ltu:diva-67456 (URN)978-91-7790-047-4 (ISBN)978-91-7790-048-1 (ISBN)
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

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