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.