Explosive detonation speed, vibration and noise in small underground mining, Zaruma – Ecuador

Abstract

The present article analyzes the relationship between Explosive Detonation Velocity (VOD), vibration, and noise generated in 16 drilling and blasting tests in two arched horizontal galleries located at different altitudes with respect to the city of Zaruma, which is situated at an altitude of 1,194 meters above sea level. Nine tests were conducted in the working face called "Apófisis," located at an altitude of 1,155 meters above sea level and 1,650 meters horizontally from the center of Zaruma. The following seven tests were carried out in the "Matamoros" face, located at an altitude of 1,116 meters above sea level and 1,389 meters horizontally from the center of Zaruma. In the "Apófisis" face, two explosive initiation systems were used: the conventional system with detonators and slow fuse, and the assembled system with quick ignition fuse, connectors, slow fuse, and detonators. The same two explosive initiation systems were also used in the "Matamoros" face. The drilled holes had a diameter of 38 mm and depths of 1.10 m and 1.50 m, aiming to maintain the horizontal shape of the gallery and parallelism between each hole (with some cases having angles of deviation ranging from 23 to 26 degrees). Both ANFO and Agricultural Ammonium Nitrate explosives were used, placed under compressed air pressure using a "gun" type pneumatic loader. The recorded data includes a minimum VOD of 3,950 m/s, a maximum VOD of 5,310 m/s, a minimum resultant vibration of 2.17 mm/s, a maximum resultant vibration of 11.5 mm/s, and minimum noise levels of 164 dB up to a maximum of 195 dB. These vibration and noise levels were compared with the current national regulations in Ecuador and international regulations in the United States. The analysis indicates that the influence of the blast in terms of VOD, vibration, and noise is within a range of 60 m to 80 m around the explosion, which does not affect the nearest infrastructure related to mining operations (offices and camps) and does not propagate to the city of Zaruma. It is important to highlight that tests using ANFO as a bottom and column charge showed lower vibrations, lower detonation velocity (VOD), and lower noise compared to the use of emulsions and agricultural ammonium nitrate.