Effect of Primer Positioning on Fragmentation: The Double-Detonator Placement and Shock Wave Collision Theory - Part 2 In rock blasting, the positioning of the primer (or detonator) plays a critical role in how shock waves propagate through the rock and ultimately impact fragmentation. One effective technique for optimizing fragmentation is the double-detonator placement, which relies on the principle of shock wave collision theory. According to Zhang (2016), when two detonators are placed at different positions within a single blasthole and detonated simultaneously, the resulting shock waves collide and create higher pressures than the sum of the original shock waves. Shock Wave Collision Theory The collision of shock waves occurs when detonators are positioned at different locations along the explosive column. As each detonator initiates its own shock wave, these waves travel through the rock mass. When the waves from the upper and lower detonators meet, they collide, resulting in an increase in the shock pressure. This phenomenon, known as shock wave superposition, leads to the formation of an area where the stresses are significantly higher than they would be from a single shock wave. According to Cooper (1996), the final shock pressure from this collision is greater than the sum of the individual shock pressures. As the detonation fronts from the two detonators overlap, the resulting high stress is concentrated in the rock, promoting fracture and improving fragmentation efficiency. Impact on Fragmentation The collision-caused high stress from double-detonator placement is highly beneficial for rock fragmentation. As the shock waves collide and combine, they create more powerful stresses that lead to improved rock breakage. When the detonation fronts from the upper and lower detonators propagate towards each other and overlap, the stress superposition region forms, as shown in attached diagram (Zhang, 2014). This region of intensified stress expands outward over time, effectively fracturing the surrounding rock. The result is a more controlled and uniform fragmentation, which reduces the need for secondary blasting or additional crushing. Optimal placement ensures that the detonation fronts overlap at the right time and location, creating the desired stress superposition region. This positioning can be adjusted based on the rock mass characteristics, blast design, and desired fragmentation results. Conclusion Double-detonator placement, based on shock wave collision theory, significantly improves rock fragmentation by increasing shock pressure and creating more effective rock fractures. By placing detonators at different positions within the blasthole, operators can optimize the stress distribution and achieve better fragmentation. This method, combined with blast result assessment tools like WipFrag, allows mining operations to evaluate the effectiveness of blast designs, ensuring more consistent and cost-effective results.
