GE 5471 ROCK ENGINEERING CH 13 Blasting Dr. Norbert H. Maerz Missouri University of Science and Technology (573) 341-6714 norbert@mst.edu Instructional Objectives 1. Explain, for a given situation, where drill and blast or mechanical excavation should be used for removing rock. 2. List the primary and secondary blasting objectives. 3. Explain the mechanisms of blasting. 4. Select and justify the type of explosive that should be used for a given situation. 5. Select and justify the type of initiation system that should be used in a given situation. 6. Explain the rationale for putting delays in the sequence of blasting. 7. List and evaluate the different methods of secondary blasting. 8. Explain the consequences of poor blasting practice. 9. Explain the differences between above and underground blasting. Blasting Objectives Science of blasting Break rock Create space Fastest time No dilution Proper size distribution Proper throw Smooth, stable walls Minimize environmental impact Mechanisms Gas pressure Shock wave Dynamic properties of rock Black Powder Dynamite ANFO Others Explosive materials Potassium nitrate, sulfur, charcoal Low detonation velocity Initiated by a fuse Black Powder 1
Dynamite ANFO Stabilized form of nitroglycerin Initiated by blasting caps Very sensitive Ammonium Nitrate (fertilizer) and Fuel Oil Initiated by more sensitive explosive Water soluble Emulsion Special needs More costly Others Initiation Systems Safety fuse Detonating cord Detonator Primer/Booster NONEL Electronic Detonators Black powder in a wrapper Burns at 7.6 mm/sec Dangerous around open flame Safety fuse High explosive in a wrapper 6.5 km/sec Low to high explosive charge Safer in open fire (shock initiated) Detonating chord 2
Electric Detonator Basting cap, to initiate main explosive Propagates at speed of electricity Subject to electrically induced misfires A highly sensitive explosive to initiate a less sensitive explosive Primer/Booster Non electric initiation system Lightly loaded detonating cord Not subject to electrical misfires NONEL Provide accurate delays Very safe Electronic Detonators Drilling Loading 3
Blast design (bench blasting) Secondary blasting Precautions Reducing ground vibrations Flyrock Airblast Ground vibrations CONTROLLED PERIMETER BLASTING Definitions Wall damage - fracturing of rock wall blasting, including crushing and radial cracking around borehole results in a weaker damaged wall Overbreak - unwanted removal of rock beyond the specified perimeter, costs money to replace with concrete, or leave a very unsightly wall Underbreak - rock remaining with the specified perimeter that should have been removed by the blast (tights) costs money to do secondary blasting 4
Perimeter Methods Blast Design (Underground Blasting) Buffer blasting Slashing Presplitting Line drilling Open hole cut Tunnel Headings Consequence of bad blasting Slide Show Flyrock, Air blast, Ground vibration damage Poor fragmentation Wall rock damage 5
Pre-Split Blasting Air track drill Loading explosives Electric detonators and wiring 6
Case History Q system to predict overbreak at Aquamilpa 7
Relationships Overbreak(%) 0.12 15.07 PPF 2.55log ( Q) Underbreak(%) 9.33 11.14 PPF 0.72 log( Q) STATISTICAL RESULTS: Rock mass quality (Q) is more likely to be the cause of overbreak, while explosive energy (PPF) is more likely to be the cause of underbreak 8
Imaging measurements of fragmentation 9
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