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Applied Research in Blast Optimization
Aimone-Martin Associates are experts in rock blasting optimization. Optimizing the blasting process begins with rock mass characterization, visually capturing the rock breakage and muckpile movement, recording explosive velocity of detonation (VOD), and close-in ground vibrations. Post-blast measurements include backbreak, fragmentation or particle size distribution, and ideally power demand on the crusher for quarry applications.
Digital
Rock Mass Characterizations
High resolution digital photogrammetry is an accurate and efficient tool for 3-D rock mass visualization and characterization.
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, or mine highwalls, or road cuts. Results can also be summarized using spherical projections, rose diagrams, and discontinuity length or area histograms. Fracture and joint spacing may be evaluated and correlated with rock blasted particle sizes as a valuable tool during blast optimization studies.
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
Velocity of detonation measurements indicate 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 backbreak.
Face Velocities
The velocity at which the free moves during detonations 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 backbreak and good fragmentation with a uniform muckpile shape.
Backbreak
Analysis
Excessive backbreak creates a dangerous highwall to work beneath as well as drill along the crest. Optimizing the blast delay timing, the use of electronic delay, and the correct distribution of explosive energy promotes highwall that are free of backbreak fractures. Our research has found that delay timing along the row is an important factor in generating backbreak fractures. Backbreak severity, as indicated by the number of backbreak and the aperture 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 backbreak.
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. Distributions of sizes are normally shown as cumulative distribution plots for sizes measured at discrete locations along the new highwall. The discrete measurement locations are the correlated with backbreak measurements along the highwall at the same positions within the blast. The variation of particle sizes and backbreak 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 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 metric for successful modifications to the blasting program.
In the application shown to the right, a comparison of crusher power during
impacting is made for fragments
produced using electronic delay technology and conventional pyrotechnic
delays.
The blast using electronic delays resulted in a 61% reduction of the 80% passing size and a 58% reduction in average power consumption during crushing compared with the data for conventional pyrotechnics, demonstrating a significant cost saving to the quarry when using electric delay technology.
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