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Multivariate evaluation of blast damage from emulsion explosives in tunnels excavated in crystalline rock
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Svensk Kärnbränslehantering AB.
EDZ Consulting AB.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

Blast damage in tunnels is usually regulated in Swedish infrastructure contracts as the extent of blast damage after excavation can affect the quality of the tunnel contour. 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. Data were compiled from several tunnel sites in Sweden and Finland where conventional emulsion explosives were used. The sites include experimental tunnels, a road tunnel, an underground depot for subway trains and a wastewater tunnel. Multivariate data analysis indicates a correlation between charge concentration and blast fracture length as well as a correlation between density of natural fractures and fracture length. A larger charge concentration increases the extent of blast fracturing and a high density of natural fractures decreases the extent of blast fracturing in the data set. The results suggest that the longer blast fractures could be more dependent on geology compared to shorter blast fractures. The initiation method seems to influence the blast fracture length but not the number of blast fractures and variance when data from conventional contour charges with simultaneous and single initiation is compared. The evaluation method was found to give indications on how blast design variables interact with different aspects of the results.

Keywords [en]
Blasting, Blast damage, Emulsion explosives, Mechanized charging, Principal Component Analysis
National Category
Geotechnical Engineering
Research subject
Mining and Rock Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-67454OAI: oai:DiVA.org:ltu-67454DiVA, id: diva2:1179595
Funder
Rock Engineering Research Foundation (BeFo)Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2018-02-01
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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