Fragmentation and Throw due to Blasting - Role of Initiation Systems

摘要

Fragmentation and muck pile profile together play an important role in optimizing the excavation costs for given geo-mining conditions. Initiation system is one of the vital parameters influencing the fragmentation and muck pile throw (profile). An attempt is made through this paper to study the characteristics of muck pile produced in addition to fragmentation. Two new parameters namely "throw-burden ratio" and "muck pile ratio" are proposed for assessing fragmentation and movement of material. Field investigations were carried out in a limestone mine in southern India with shock tube and detonating cord initiation, using four initiation patterns, keeping other parameters like burden, spacing, delay timing etc. same.Muck pile resulting from every blast was surveyed and throw distance was monitored. The muck pile throw was higher in detonating cord initiated blasts as compared to shock tube initiated blasts, requiring deployment of a dozer to augment shovel loading. As throw of fragmented material is related to burden rock movement, muck pile throw distance to burden relationship of throw-burden ratio was developed. This ratio varied between 3.14 and 9.14 for different blast patterns. The throw-burden ratio was smaller for shock tube initiated blasts. V-pattern of initiation resulted in lowest throw-burden value compared to diagonal pattern of initiation followed by row to row pattern of initiation.Muck pile height to bench height relationship was developed as Muck Pile Ratio. This ratio was used for comparing the productivity of the excavator. An attempt was made to calculate the muck pile volume based on muck pile profile survey. Shock tube initiated blasts resulted in higher productive yield compared to detonating cord initiated blasts, as throw was less in shock tube initiated blasts. The productive yield was around 95% for shock tube initiated blasts, whereas it was around 90% for detonating cord initiated blasts. In shock tube initiated blasts, the remaining 5% volume of fragmented material was spread over 10% to 12% planar area. In detonating cord initiated blasts, remaining 10% volume of muck pile was spread over about 30% planar area. This condition demands the deployment of dozer for piling up fragmented material augmenting the loading process. To ascertain validity of the newly proposed parameters, fragmentation from these blasts was further analyzed using digital image processing and boulder count methods. Fragmentation analysis using digital image processing technique showed that average fragment size (K50) values were higher by 25% to 32% in detonating cord initiated blasts, indicating larger sized fragmentation, compared to shock tube initiated blasts.