94A

then action by residual pressure in the borehole to form the crater. Feasibility of this mechanism is checked using finite element analysis.

942264 Idea on determining optimum firing direction for bench blasting Adhikari, G R J Min Metal Fuels V41, N2/3, Feb-March 1993, P52-53

Suggestions are made for a procedure to determine optimum firing direction for blasting a rock mass containing one or more prominent joint sets with the minimum number of trial blasts. Trial blasts are carried out with varying firing direc- tions and the P wave velocity of the rock mass is measured in different directions. Correlations are sought between blast per- formance and some (minimum, maximum, or other) value of P wave velocity.

942265 Development drilling problems in high-pressure reservoirs French, F R; McLean, M R J Pet Technol V45, N8, Aug 1993, P772-777

The fracture gradient, the pressure gradient at which a frac- ture develops in the wellbore wall and large mud losses occur, must be taken into account for successful drilling operations. Field interpretation of fracture initiation and propagation gra- dients is examined. It is found that interpretations from explo- ration wells may not be sufficient for safety of development drilling. A case history from an overpressured North Sea res- ervoir is presented. It is suggested that microfracturing might be used to resolve inherent uncertainties in planning develop- ment wells in overpressured reservoirs.

942266 Comparison of the theoretical and measured velocities of detonation for selected explosives Louw, M J; Sarracino, R S; Vather, S M J S Aft last Min Metall V93, N6, June 1993, P147-153

Velocities of detonation of ANFO, a bulk emulsion, and 3 repumpable emulsions were predicted under various condi- tions of hole diameter and confinement using the detonation models IDeX for ideal VOD and CPeX for non-ideal VOD. Predictions are compared to in-hole VODs. Results are within experimental error for ANFO and the bulk emulsion but are inconsistent for the pumpable emulsions. These discrepancies can be explained as due to variations in mining and loading practices. The detonation models are useful predictive tools provided the user is aware of in-mine factors which can affect explosive performance.

942267 Rock blasting techniques in opeocast coal operations Hartley, R Quarry Manage Sept 1993, P35-39

The two most common forms of bulk rock blasting in open pit coal mining are buffer blasting, where minimum ground move- ment is required to break the rock, and east blasting, with horizontal rock movement maximised to produce a thrown muck pile. Presplitting is often employed with the latter tech- nique. In the UK, where minimum environmental impact and safety are paramount, buffer blasting is employed. In South Africa, where larger blasts and isolated locations are the norm, cast blasting is more widely used.

Crushing and grinding

942268 Model of mill power as affected by mill speed, load volume and liner design Moys, M H J S Aft last Min MetaU V93, N6, June 1993, P135-141

Models of mill power are briefly reviewed. A new semi-phe- nomenological model is derived, in which the conventional torque-arm model is combined with a model of the tendency of the load in the mill to centrifuge at high speed. Mill power can be related to design variables such as mill geometry, speed, and liner design and to control variables such as load volume, slurry theology, and, in the case of variable speed milling, mill speed. This new model more accurately describes real beha- viour than do empirical models such as the Bond model.

942269 Application of vibration signals to monitoring crushing parameters Zeng, Y; Forssberg, E Powder Tecitnol V76, N3, Sept 1993, P247-252

Vibration signals from a laboratory scale jaw crusher have been monitored and recorded during crushing of dolomite. The time domain vibration signal has subsequently been analysed using a digital signal processing technique. Variation in vibration pattern can be described by a few variables, obtained by principal component analysis, which can in turn be correlated with crusher setting and product size using mul- tiple regression. This work may form the basis of a new method of monitoring the crushing process.

Machine excavation

942270 Design of cutter heads for optimum cutting powers (In German) Frenyo, P; Lange, W Giuckauf V129, N7, July 1993, P524-532

Cutting tests have been carried out using different tools on a range of coals, evaporites, sandstones and conglomerate. Required cutting forces varied by an order of magnitude for the same pick across the range of minerals, suggesting there can be no one all-pupose cutting head design. It is recom- mended that a short trial run be carried out using a presuma- bly suitable cutter head and measured values used as a basis for final design.

942271 Large dozer stripping case studies Hrebar, M J Min Engng V45, N9, Sept 1993, P1185-1189

The use of large tractors as primary stripping machines and in combinations with blast casting, draglines, and excava- tor/truck systems has been investigated at surface coal mines. Production rates and economic analysis in contour stripping and overburden removal on a blasted bench are described and discussed.

Rock ami Soil Reinforce nt and Support

See." 942322