Blasting surface rocks in open-pit mining operations and quarries necessitates striking a balance between fragmentation, excavation efficiency, and safety standards. Choosing the right type of bulk explosives (ANFO, bulk emulsions, or Heavy ANFO blends) relies heavily on rock properties, drilling parameters, and water presence. Uncontrolled water in blast holes represents an extreme challenge, causing explosive desensitization, deflagration, NOx fumes formation, and inadequate toe cutting. Modern blast design solves the above problems through a special choice of product, unique water decking technologies, and site hazard management.
ANFO is oxygen-balanced explosive (94.4% AN and 5.6% fuel oil) with bulk density of 0.82-0.90 g/cc and inexpensive heaving capacity in dry holes. ANFO is not water resistant and, when exposed to water, dissolves fast, causing either misfires or inefficient low-order detonation that produces orange NOx fumes. In contrast, bulk emulsions are explosive products that have aqueous oxidizing solution inside a continuous fuel phase and, therefore, 100% waterproof.
Emulsions also have high bulk densities (1.00-1.20 g/cc) and gassing agent sensitivity and, thus, produce higher velocity of detonation (VOD) and loading density (by 45% in comparison with ANFO). The last option –Heavy ANFO blends – includes ANFO and emulsions and allows custom density, wider drill patterns and better water resistance. Waterproof blends (60%-70% emulsion) are loaded from the hole bottom, thus displacing the water without mixing with the product.
If the full hole dewatering is unfeasible, the Water Deck Blasting (WDB) technique becomes effective. Using a structural separation, which can be the hydrophobic powder, placed on top of toe water, the explosive column becomes totally separated from water. Separating allows to detonate the ANFO in dry conditions and transforms the bottom water column into an energy-capturing layer. The numerical modeling and field tests show that the WDB provides multiple shock wave oscillations, dynamic stress duration extension, lack of hazardous fumes, and excellent rock fragmentation with a flat bench floor.
Safety of the operation presupposes precise drilling logging, profiling with lasers and bores tracking for avoiding flyrocks, overpressure, and wall instability. Environmental compliance involves prohibition of using perchlorate initiators and controlling of bulk loading for avoiding the water pollution. On-bench controls involve checking of gassing density prior to stemming, exclusion zone control, and bottom-up loading when pumping liquid products.
To sum up, optimal blasting efficiency is dependent on a proper correlation between the explosives used and the geologic and hydrologic properties at the site. Effective use of bulk emulsions or application of the technique called water deck blasting will ensure that the explosives remain unaffected by water damage, no toxic fumes are generated, and efficient usage of the explosive energy is attained.
