In this study, the plaster stemming application for blasting at a basalt quarry is studied. Drill cuttings are generally used in open pits and quarries as the most common stemming material since these are most readily available at blast sites. However, dry drill cuttings eject very easily from blastholes without offering much resistance to blast energy. The plaster stemming method has been found to be better than the drill cuttings stemming method due to increased confinement inside the hole and better utilization of blast explosive energy in the rock. The main advantage of the new stemming method is the reduction in the cost of blasting. At a basalt quarry, blasting costs per unit volume of rock were reduced to 15% by increasing burden and spacing distances. In addition, better fragmentation was obtained by using the plaster stemming method. Blast trials showed that plaster stemming produced finer material. In the same blast tests, +30 cm size fragments were reduced to 47.3% of the total, compared to 32.6% in the conventional method of drill cuttings stemming. With this method of stemming, vibration and air shock values increased slightly due to more blast energy being available for rock breakage but generally these increased values were small and stayed under the permitted limit for blast damage criteria unless measuring distance is too close.
ResumoAparas e pó de perfuração são, geralmente, utilizados em pedreiras e minas a céu aberto, como o material de tamponamento mais comum, uma vez que são mais facilmente disponíveis nas frentes de desmonte. O tamponamento com gesso mostrou-se de melhor uso do que o com detritos de perfuração, devido ao aumento do confinamento dentro dos furos e melhor utilização da energia explosiva no desmonte do maciço. A principal vantagem do novo método é a redução do custo do desmonte. Em uma pedreira de calcário, os custos de detonação por unidade de volume de rocha desmontada foram reduzidos em 7%. Isto foi obtido através do aumento da carga e distâncias de espaçamento. Além disso, a melhor fragmentação foi obtida, usando-se o método de tamponamento com gesso. Ensaios de detonação mostraram que o uso do gesso produziu material mais fino do que os métodos convencionais. Em ensaios sob mesmas condições, a geração de matacões acima de 20 cm de tamanho foi de 42,6% do total, comparado com 48,7% no método convencional, usando-se espaçadores e tamponamento de aparas de perfuração.
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Numerical simulation of the plaster stemming method (PSM) was performed and compared with the conventional drill cuttings stemming method (DCSM). Many earlier in situ tests have proved that PSM can use the blast energy more efficiently than DCSM. Despite PSM generating more blast vibrations, it has advantages over DCSM such as better fragmentation and lower cost per unit volume of rock blasted. In this study, numerical simulation with Autodyn software using a 2D tool was employed to prove the efficiency of plaster stemming by comparing parameters such as pressure, Y-velocity, Y-force, internal energy, acceleration-Y, and compression. For example, the maximum pressure attained at the top of explosive column was 7 395 MPa for DCSM whereas it was as high as 11 945 MPa for PSM. Most of the computed parameters were significantly higher in PSM than those obtained for DCSM. This paper is the first study elucidating the efficiency of PSM by numerical simulation. It is concluded that PSM can save substantial amounts of money and effort.
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