Numerical study on the effectiveness of mechanical rock bolts in an underground opening excavated by blasting

l12A holes. This is an analogue of a pressurised hole with diametrical notches along its length. The equivalent notched hole concept has been investigated in the laboratory in plexiglas and in a quarry bench of highly jointed limestone. Geometry and hole spacing limitations of the technique are discussed and it is compared with other controlled blasting methods. 932314 Effect of explosive type on fines generation in blasting Sheahan, R M; Beattie, T A Proc 3rd International Symposium on Rock Fragmentation by Blasting, Brisbane, 26-31 August 1990 P413-415. Publ Parkville: AuslMM, 1990 Fragmentation performance of a range of A N F O explosives was examined in small scale trials in a granite quarry. 65mm blastholes were fired simultaneously in a 5m bench and rock collected, sieved, and weighed. A linear relation is seen between fines production and effective energy. The mass of fines remained the same as the pattern was expanded, suggesting fines are formed around the borehole. Strong decoupling significantly reduces the amount of coarse material, but not the fines. Lengthening the period of energy delivery improved fragmentation. Explosive energy correlated well with face velocity. 932315 Factors affecting explosive sensitivity Armstrong, L W; Torrance, A C; Moxon, N T Proc 3rd International Symposium on Rock Fragmentation by Blasting, Brisbane, 26-31 August 1990 P417-422. Publ Parkville: AuslMM, 1990 Glass microspheres (GMS) are commonly used to sensitise emulsion explosives. GMS integrity is critical to explosive performance. The effects of damage caused by production of a typical GMS sensitised emulsion, use of different strength detonating cords, and of the variation of percentage of broken GMS as supplied by the manufacturer have been studied. Poor initiation can reduce available G M S by 50%. Based on these laboratory tests, suggestions are made for design of GMS sensitised explosive charges. 932316 Numerical study on the effectiveness of mechanical rock bolts in an underground opening excavated by blasting Chua, K M; Aimone, C; Majtabai, N Proc 33rd US Symposium on Rock Mechanics, Santa Fe, 3-5 June 1992 P285-293. Publ Rotterdam: A A Balkema, 1992 Smooth wall blasting is often used in underground excavations in hard, fine grained rock. To ensure rock reinforcement schemes are effective, it is necessary to know the extent of damage caused by the blast. Damage zone estimation is described. A three dimensional elastic wave propagation code was modified for application to underground blasting and used with the damage criterion of Grady and Lipkin (1980). Effectiveness of rock bolting is assessed using the finite element code GEOT2D. The analysis presented uses properties of the welded tufts from the Yucca Mountain Project. 932317 Computer modeling of gas flow and gas loading of rock in a bench blasting environment Preece, D S; Knudsen, S D Proc 33rd US Symposium on Rock Mechanics, Santa Fe, 3-5 June 1992 P295-303. Publ Rotterdam: A A Balkema, 1992 Detonation of an explosive in a blastwell produces a transient stress wave which fragments the rock and a high pressure, high temperature gas pocket which expands and pushes the rock in

front of it. The spherical element computer code DMC (Distinct Motion Code), originally developed to simulate blasting in a cratering environment, has been modified for application to bench blasting. It is used to study variation in face velocity as burden, blastwell diameter, and explosive type are altered. 932318 Effects of blasting practices on fragmentation Stagg, M S; Otterness, R E; Siskind, D E Proc 33rd US Symposium on Rock Mechanics, Santa Fe, 3-5 June 1992 P313-322. Publ Rotterdam: A A Balkema, 1992 An outline is presented of results of tests carried out by the USBM over the last decade to define relations between blast parameters and resulting fragmentation. Empirical relations developed to describe effects of explosive energy, decoupling, and rock mechanical properties are given. Predicted and measured fragmentations from test and full scale blasts are compared.

Crushing and grinding 932319 Mechanism of action of grinding aids in comminution Moothedath, S K; Ahluwalia, S C Powder Teclmol V71, N3, Sept 1992, P229-237 Specially designed experiments in a laboratory ball mill were used to study the mechanism and action of grinding aids on attrition and breakage in comminution. Small amounts of grinding aid assist attrition of limestone, excess amounts have the reverse effect. No change is seen in impact breakage rate of (-10 + 14) mesh material as a result of use of grinding aids. The theory of easier crack propagation due to reduction of surface energy cannot explain the effects of grinding aids in this case. Improvement of flowability, reduction of fines aggradation, and reduction in ball and mill wall coating can explain the enhancement.

Machine excavation See a~o: 932291 932320 Cuttability measurement as a basis for determining the plonghability of coal seams (In German) Paschedag, U; Schwolow, G Gluckauf-forschungsh V53, N2, April 1992, P63-67 Cuttability measurements made by the DMT using a technique comparable to ploughing are correlated with results from a reference plough working the same coal. The reference plough design is used as a basis for design of other plough installations. Simple nomograms are presented which make it possible to dimension a plough installation such that it matches the ploughability of the coal. 932321 Wear characteri~tion of rock Fowell, R J; Gillani, T; Altinoluk, S Proc ISRM Symposium: Eurock '92, Chester, 14-17 September 1992 P13-18. Publ London: Thomas Tel_ford, 1992 Drag pick consumption rates in tunnelling machines depend on many rock, tool, and machine parameters. In an attempt to characterise some of these effects, drag pick tools were mounted on a workshop vertical boring machine and used to cut a range of sandstones, typical of sedimentary strata in which drag picks are used. The influence of rock properties,

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