Controlled blasting in hard intense jointed rock in tunnels

Abstract Falling rock is one of the major causes of serious injuries and deaths in Swedish mines. The research at the Division of Mining and Underground Construction was therefore directed toward controlled blasting in hard intense jointed rock.
The project was started with an extensive literature review. Model tests with a new equivalent model material have been initiated to find ways of improving blasting techniques. The result showed that long cracks arise at the perimeter holes when there is a long time delay between adjacent holes. This led to the theoretical development of a new initiation method with ultra short delays (1,5 ms)for controlled blasting, called "Cutblasting".
Full-scale tests have been done at LKAB in Malmberget in hard intense jointed magnetite ore. Four different types of perimeter charges have been tested, namely: tube charges, ANFO mixed with plastic beads, detonating cord and linear-shaped charges. Three types of initiation of the perimeter holes have been used, conventional (half-second delay detonators), instantaneous and ultra short "cutblasting initiation" (1,5 ms delay). The change in rock strength before and after blasting has been studied with bore hole periscope, vibration measurement and ocular observation of the rock surfaces.
The full-scale tests showed that "cutblasting" with detonating cord in the perimeter holes gave the smallest damage to the surrounding rock. A combination of cutblasting initiation and tube charges are anticipated to give an even better result. A new method of controlled blasting using linear-shaped charges has also been tested, however, this charge type needs further development.
The full-scale test also showed that the damage which can be seen on the rock surface is about the same for different controlled blasting methods but the not-visual-damage zone varies as much as from 0,1 to 0,7 m. A new classification system for controlled blasting regarding the damage to the surrounding rock has been devised.
Keywords: Rock mechanics, Controlled blasting, Hard intense jointed rock, Rock stability, ANFO, Explosives, Cutblasting, Blasting, Drilling, Initiation techniques, Vibration measurements.
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Publication: CIM Bulletin
Author(s): F.J. MUNN
Keywords: Rock mechanics, Pitwall stability, Wall failures, Coal mining, Wall control, Monitoring, Backfill, Cardinal River Coals Ltd.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: This report describes the development and effective use of shaped charges as part of the Elliot Lake Mine Roof Stability Project to remotely remove the heads from roof bolts. With a slight modification, these same shaped charges are being recommended for use to the Brunswick Mining and Smelting Corporation Limited (Mining Division), to cut steel cable bolts.
Publication: CIM Bulletin
Author(s): E. CONTESTABILE, T.R. CRAIG
Keywords: Rock mechanics, Shaped charges, Roof stability, Cable bolts, Explosives, Support systems, Loading.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: The selection of material comprising a backfill is, of economic necessity, site dependent. Nevertheless, given the existing range of typical components—coarse waste, alluvial sand, tailings— a balanced or optimal choice is no straightforward matter. A new design approach toward deciding what constitutes an optimum combination of backfill material promises to be useful. In particular a 'binder' number, based on the mean distance between aggregate particles, specific surface and...
Publication: CIM Bulletin
Author(s): G. SWAN
Keywords: Rock mechanics, Mine backfill, Backfill design, Mill tailings, Aggregates, Grading, Cement, Compressive strength.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: Equity Silver Mines Limited, Canada's largest silver mine, has designed, built and operated a leach plant to reduce the levels of antimony and arsenic in its silver-gold-copper flotation concentrate. The orebody contained deleterious antimony and arsenic minerals in such proportions that the economic long-term sales contracts necessary to obtain project financing could not be procured. Construction of the leach plant therefore allowed development of the mine to proceed. Although the plant...
Publication: CIM Bulletin
Author(s): C.R. EDWARDS
Keywords: Process development, Filtering, Leaching, Plant design, Process technology, Antimony, Arsenic, Silver.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: Competition in the world potash market has increased significantly since the late 1970s. The failure of consumption to grow at expected levels has led to industry over-capacity, a situation which is likely to persist at least until 1990. Individual Saskatchewan producers and their offshore marketing company, Canpotex, have responded to this challenge by increasing mining efficiency, developing more cost-effective and reliable transportation systems and establishing innovative financing and...
Publication: CIM Bulletin
Author(s): DOUGLAS A. KARVONEN
Keywords: Industrial minerals, Potash, Marketing, Domestic market, Offshore market product development, Transportation, Potassium chloride, Fertilizers.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: A sample of flotation feed from Bakertalc Inc., Highwater, Quebec was subjected to flotation evaluation to improve the recovery of talc. A number of alternative frother/collectors and depressants as well as flotation parameters including pH, conditioning time, frother/collector concentration and pulp density were assessed. In addition, the possibility of using a size coarser than that currently employed for flotation (95% minus 50 /j,m) was investigated.
As far as possible, a laboratory...
Publication: CIM Bulletin
Author(s): P.R.A. ANDREWS
Keywords: Industrial minerals, Talc, Flotation, Recovery, Milling, Grinding, Processing, Frothers, Depressants.
Issue: 884
Volume: 78
Year: 1985
Text
Summary: This paper describes a methodical approach to the estimation of the orientation and the magnitude of in-situ stresses. The study was performed at the Ruttan Mine, Sherritt Gordon Mines Ltd., a 6,000 T.P.D. underground operation, located in northern Manitoba, Canada. It involves an initial estimate to be made based upon:

structural interpretation
virgin stress measurements conducted in other areas (world wide, regional)

 The verification of the prevailing stress regime was...
Publication: CIM Bulletin
Author(s): R. PAKALNIS, H. MILLER, T. MADILL
Keywords: Rock mechanics, In-situ Stresses, Virgin stress measurements, Structural geology, Fractures, Boreholes, Debonding, Overcoring.
Issue: 884
Volume: 78
Year: 1985
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