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Recent Swedish Studies on the Extent of Blast Damage after Excavation
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Swedish Nuclear Fuel and Waste Management Company (SKB).
Swedish Transport Administration (TRV).
Swedish Nuclear Fuel and Waste Management Company (SKB).
EDZ Consulting AB.
Show others and affiliations
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.

Place, publisher, year, edition, pages
2016.
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-39564Local ID: e60f1a29-4bed-4969-b2d3-a702d938deb5OAI: oai:DiVA.org:ltu-39564DiVA, id: diva2:1013078
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
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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