Abstract
Nine blasts with cylindrical granite specimens were carried out under different stemming conditions. All rock specimens had a diameter of 240 mm and a length of 300 mm. Explosive Pentaerythritol tetranitrate (PETN) with specific charges 0.2 and 0.3 kg/m3 were used, and the blasts were carried out in a large explosion chamber. Each rock specimen was enclosed by a steel box in the chamber during blasting, without constraint or confinement to the specimen from lateral and top sides. During blasting a high-speed camera was used to film the blasting process and monitor the gas ejection. After each blast all fragments were collected, sieved and analyzed. The experimental results showed that: (1) the blasts with full sand stemming yielded better (finer) fragmentation than the blasts with partial steel stemming at a constant specific charge, and (2) gas ejection from the collars of blastholes occurred much earlier in the blasts with partial steel stemming than in the blasts with full sand stemming. Based on the experimental results, it can be concluded that it is extremely important to prevent gas ejection from the collars in order to achieve desirable rock fragmentation.
Highlights
Hard rock mining and hard rock excavation require a huge amount of explosive energy
Because stemming is related to energy efficiency and ore recovery and dilution in mining engineering,[4,14,15,16,17,18] it is necessary to investigate the effect of stemming conditions on rock fragmentation quantitatively
The explosive Pentaerythritol tetranitrate (PETN) with a critical diameter of 1–1.5 mm[4, 51] was used in this study since blastholes were small. This raw PETN explosive had a density of 0.93 g/cm[3], explosion heat of 5925 kJ/kg, and a velocity of detonation (VOD) of 5300 m/s
Summary
Hard rock mining and hard rock excavation require a huge amount of explosive energy. the energy efficiency in rock blasting is very low.[1,2,3,4] It has been found that stemming takes a great part in the utilization of explosive energy in rock blasting.[1,4,5,6,7,8,9,10,11,12,13] For example, field measurements in an underground gold mine[8] showed that the high-speed gases carried away much explosion energy through the col lars of unstemmed blastholes. Most blasts in upwarddrilled and horizontally-drilled boreholes are either not stemmed or only stemmed using a very small plastic plug or similar material as stemming. Because stemming is related to energy efficiency and ore recovery and dilution in mining engineering,[4,14,15,16,17,18] it is necessary to investigate the effect of stemming conditions on rock fragmentation quantitatively. Such an investigation can be performed by either full-scale field blasts or small-scale model blasts. In the last part of the paper, some issues con cerning stemming conditions were discussed
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