921298 Analysis of explosions in hard rocks: the power of discrete element modelling Heuze, F E; Walton, O R; Maddix, D M; Shaffer, R J; Butkovich, T R Proc International Conference on Mechanics o f Jointed and Faulted Rock, Vienna, 18-20 April 1990 P21-28. Publ Rotterdam: A A Balkema, 1990

Discrete element modelling, applied in conjunction with realis- tic fragmentation models, can trace discrete particles resulting from explosions and describe their dynamic interaction. Fea- tures of the DIBS (Discrete Interacting Block System) code developed by the Lawrence Livermore National Laboratory are described and its use to simulate a cratering test in dry basalt is illustrated. A second simulation uses DIBS and UDEC to describe detonation in an array of planar boreholes in granite. Finally a deep, contained explosion is modelled.

Crushing and grinding

921299 Coal crushing for minimum fines Schutte, H O W S Af t Min World VIO, N2, March 1991, P32-37

Effective crushing means minimum of fines, power, and cost, plus a product of good size distribution. The crushing actions of jaw, impact, hammermill, single roll, and double roll crush- ers are described. Screening to avoid crushing material already in the correct size range is essential. Low crushing ratios, mul- tiple pass crushing, and use of secondary crushers should be used. Features to be considered in selection of the right crusher, calculation of crushing capacity, and maintenance of optimum performance are discussed.

Machine excavation

921300 Design guidelines for picks Powell, F Colliery Guard V239, N5, July 1991, P139-141

Selection of tools for cutting quartzitic rocks in coal mines must be made with due consideration of cutting rate, dust make, risk of sparking, and economics. Tests carried out using point attack, radial, and forward attack picks with various tool tip materials are reported. Large round-nosed tips, prefer- ably attached to forward attack picks are recommended, with extra tough tungsten carbide tips with PDC layers on the rake face. Correctly designed water sprays minimise the risk of igni- tion of air/methane mixtures.

921301 BoreabUity assessments for the Lesotho Highlands Water Project Blindheim, O T; Richards, L A Tunn Tunnlg I1"23, N6, June 1991, P55-58

The size of the LHWP and the lengths of TBM drives envis- aged make estimation of advance rates important to both owner and contractor. The project is in the Karoo Basin with sedimentary rocks capped by basalt flows. A variety of indi- rect tests is available to predict TBM boreability. These are summarised and their bases described. The Norwegian Insti- tute of Technology (NTH) and linear cutting tests were used in the case of the transfer tunnel (basalt) and NTH and total hardness tests for the delivery tunnel (sedimentary rocks).

39A

921302 Underground mining of frozen placer deposits in USSR Evsiovich, A S; Kudlay, E D; Dushkin, A N Proc 1st International Symposium on ~Wining in the Arctic, Fairbanks, 17-19 July 1989 P241-244. Publ Rotterdam: A A Balkema, 1989

Mining of frozen placer deposits presents a lot of problems due to their small sizes, remote locations, severe environmen- tal conditions, and other geological parameters. Research aimed at developing specific mining methods for these deposits was conducted. Whilst the current extraction methods of fro- zen placers are based on drilling and blasting, mechanical breakage of frozen materials has been developed. Some of these methods utilise continuous miners and other mechanized extraction machines.

921303 Assessment of open pit excavators diggability Panagiotou, G N Proc 2nd International Symposium on Mine Planning and Equipment Selection,Calgary, 7-9 November 1990 P305-314. Publ Rotterdam: A A Balkema, 1990

The requirements of large tonnages from open pit mines neces- sitates the utilisation of large machines. Excavators are usually selected based on diggability. The parameters of the rock mass are often used to determine the diggability criteria. However, rock parameters alone cannot adequately determine dig- gability. Machine characteristics and geology are also impor- tant in selecting which type of excavator will be used or whether ripping or blasting is required. A quantitative appr- oach to assessing diggability is proposed, using equipment- ground interaction models. Its application to assessing bucket wheel excavation and to plotting diggability maps is presented.

921304 Rippability assessment in surface coal mining Karpuz, C; Pasamehmetoglu, A G; Bozdag, T; Muftuoglu, Y Proc 2nd International Symposium on Mine Planning and Equipment Selection,Calgary, 7-9 November 1990 P315-322. Publ Rotterdam: A A Balkema. 1990

Rippability studies can be categorised into those that employ rippers in the field and those that correlate ripping assessment and the rock mass properties. Studies were conducted to assess the rippability for the rock types encountered in coal mines, with emphasis on geological parameters, seismic velocity mea- surement, and laboratory tests to determine rock properties. Based on these tests, rippability charts including proposed rip- per types have been produced. Details of the analysis and the obtained design charts are presented.

Hardness, abrasion and wear

921305 Wear mechanisms associated with rock excavation using attack picks Rogers, S; Roberts, B g i n Sci Technol VI2, N3, May 1991, P317-323

Simple models used to study wear of surface mining equip- ment are inappropriate for roadheader cutting, where cutting and transient forces are much greater. Existing wear models are outlined and the forces and friction acting on the cutting tool as it passes through rock are analysed. Possible wear paths are discussed. A complex and composite mechanism is probable, with frictional heating and very high pick forces playing significant roles. Water spray cooling and limititation of depth and speed of cut will lower tool wear rate.

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