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Blast Optimization

Aimone-Martin Associates are experts in rock blasting optimization. Optimizing the blasting process involves drilling accuracy and efficiency, profiling exposed highwall faces for mining applications, tailored loading explosives according to highwall face and rock conditions at depth, and designing proper delay timing and initiation sequence.

Diagnostic tools and measurements are key to blasting success and may include rock mass characterization photogrammetry, recording explosive velocity of detonation (VOD), visually capturing face velocities, rock breakage, and muckpile movement during the blast, and recording close-in ground vibrations both on the surface and at depth.

Post-blast measurements include back break, fragmentation or particle size distribution, and for quarry or construction crusher applications, power demand on the crusher.

 

Digital Rock Mass Characterizations

Recent developments in high resolution digital photogrammetry provide an accurate and efficient tool for 3-D rock mass visualization and characterization. Low-cost methods are available today

Three-dimensional surfaces consisting of tens of thousands to hundreds of thousands of xyz points are created from pairs of high-resolution digital photographs, then used to map discontinuities in natural outcrops, quarry and mine highwalls, or road cuts. Results can also be summarized using spherical stereonet projections, rose diagrams, and histograms of discontinuity lengths or surface areas.

Naturally occurring rock fracture and joint spacing may be evaluated using photogrammetry and correlated with rock blasted particle sizes as a valuable tool during blast optimization studies. This is an important and cost-effective rock characterization tool. Photogrammetry analysis can used to predict geological controls on blast fragmentation results, important when modifying blast design parameters.

Advantages of digital photogrammetry over terrestrial laser scanning include portability of field equipment, accuracy and speed of data acquisition, and a finished 3-D model with integrated rock structure as opposed to a draped mesh.

 

 

 

 

 

 

 

 

VOD Measurements

In-hole velocity of detonation (VOD) measurements are the best indicators of explosives performance. Optimum VOD, based on charge size and explosives properties, is important to the energy available to break and heave the rock. Poorly performing explosives must be evaluated as low VOD values may adversely affect fragmentation, vibrations, and back break.
 


Face Velocities

The velocity at which a highwall face moves during detonation is important to utilization of explosive energy and is chiefly controlled by the front row burden, delay timing, and borehole conditions. Optimum face velocities result in minimum back break and good fragmentation with a uniform muckpile particle size distribution shape.

Backbreak Analysis

Excessive back break behind the crest of a newly formed highwall after blasting creates a dangerous highwall to work beneath as well as a crest along which to drill. Optimizing blast delay timing, the use of electronic delays, and using the correct distribution of explosive energy promote highwalls free of serious back break fractures. Our research has found delay timing along the row is an important factor in generating back break fractures. Back break severity, as indicated by the number of cracks behind the crest and the aperture (or width) of the fractures, is normally correlated with rock particle sizes. The larger the rock fragments, the less energy was used for muckpile breakage, the greater the intensity of fractures along the highwall. Finer fragmentation is generally correlated with the absence of back break. This is not a new concept. We now have the data from numerous mines to show the correlations.

 

Fragmentation Analysis

Measurements of blasted rock particles are performed using digital photographs and an edge-detecting algorithm to outline particle shapes for area and size computations. The range of blasted rock sizes are normally shown as cumulative distribution plots for sizes measured at discrete locations along the new highwall. The discrete measurement locations are then correlated with back break measurements at the same positions within the blast. The variation of particle sizes and back break fractures are parameters used to define, in part, blasting efficiency.

 

Monitoring Crusher Power for Quarries

Digital power meters can be integrated into the crusher motor circuit to record and store power demand of the crusher during primary size reduction of blasted rock. Monitoring power demand on the motor provides an excellent tool used for successful blast design modifications.

In the application shown to the right, a comparison of crusher power demand during impacting is made for fragments produced using electronic delay technology and conventional pyrotechnic delays.

The comparison is dramatic. The blast using electronic delays resulted in a
61% reduction of the 80% passing size and a 58% overall reduction in average power consumption during crushing compared with the data for conventional pyrotechnics. This quarry study demonstrated a significant cost saving to the quarry when using electronic delay technology.

 

 


 

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