Burden Dynamics and Fragmentation

Drill and blast is a dominant technique in several surface and underground mines in the world. The purpose of this technique is to break rock mass into fragments, which can be handled by mining equipment. The identified major influencing factors in rock blasting are stress waves and gas pressurization. In underground mines, especially in sublevel caving mines, the blast is performed under confined conditions. Hence, one more category of mechanisms has to be taken into consideration which describes the behavior of granular materials. Several small-scale tests have been conducted in order to define parameters which affect fragmentation by blasting as well as to measure the burden behavior during blasting. The purpose of these tests was to investigate how firing pattern, confinement and inter-hole delay time influence the fragmentation. Additionally, an incremental relative distance sensor was developed to measure the burden movement during blasting. The results showed that the burden moved with a velocity of approximately 29 m/s. The V-shaped firing pattern gave coarser fragmentation compared with sequential firing pattern for both the blasted material and confining material.After the small-scale tests, a zero pillar test was conducted under confined conditions to evaluate and validate a newly developed measuring system. The purpose of this system was to measure the burden dynamics. The system was calibrated in laboratory conditions under dynamic loading. This system was based on a piston-like structure and it was equipped with accelerometers and a potentiometric distance sensor. In addition to the measuring system, several installation and initiation procedures have been developed. The results of the measuring system showed that the burden moved 0.98 m at a velocity of 17-18 m/s. All the procedures performed as well as expected and designed.In addition to the study of blasting related mechanisms, the results of a blast also have to be measured. Sieving is usually not an option for large scale operations due to high costs. The alternative way is to implement digital image analysis. This procedure does not interfere with the production of a mine. Several trials have been conducted at the Aitik open pit mine to investigate the influence of short inter-hole delay time (1 ms, 3 ms and 6 ms or 0.14 ms/m burden, 0.43 ms/m burden and 0.86 ms/m burden) on fragmentation. The examined mechanism was the interaction of stress waves between neighboring blastholes. The fr