Models for assessing the blasting performance of explosives

The blasting performance of an explosive in a given situation is dependent on its detonicnproperties, the rock mass response to explosive loading and the confinement provided bynthe blast design. The blasting performance of an explosive can be assessed in terms ofnfragmentation, muck pile shape and looseness and the damage resulting from the blast.nnnnnnnnnnn n A mechanistic model has been developed in this thesis to estimate the energy released bynan explosive during blasting operation. The blasting process is classified into fourndiscrete time events to describe the detonation phase, shock wave propagation phase,ngas pressure expansion phase and burden movement phase. The model mimics thenblasting process and estimates the energy released by the explosion gases during eachnphase.nnnnnnnnnnnnnn n The important features of the model are: nbnIt takes into account the effect of explosive-rock interaction and confinementnprovided by the burden and stemming while calculating the energy. nbnIt partitions the explosive energy into several components based on the phasenin which it is released and how it is utilised. nbnIt also outputs the complete pressure-time history of the explosion gasesnduring the blasting process.nnnnnnnn n A fragmentation model has been developed based on comminution theory to predict thenaverage fragment size and fragment size distribution. The model uses the fragmentationnenergy (i.e energy utilised in the fragmentation processes) estimated by the explosivenenergy model to predict the frag mentation.nnnnnnnnnn n A model has been developed to estimate the damage caused to the surrounding rocknmass by a blast. The model predicts the crushing zone (resulting fines), extent of shock-induced radial fractures and their extension due to gas penetration. The pressure-timenhistory estimated by the explosive energy model is used as an input in this model.nnnnnnnnnn n Blast monitoring studies were conducted at two op en pit mines to obtain the datannecessary to understand the explosive-rock interaction. A monitoring procedure wasndeveloped to study the effect of confinement on gas penetration into the fracture networknbehind the blasthole. The data were also used to validate the models developed in thisnthesis. The gas penetration monitoring studies revealed that confinement has ansignificant influence on gas penetration.nn n The data from six case studies were used to estimate the partition of energy released byndifferent explosives using the model developed in this study. These energy estimatesnwere compared with the standard energy values estimated from ideal detonation codesnand underwater energy measurements. The different components of explosive energynestimated by the model were correlated with the measured blasting performancenindicators such as fragmentation, throw and crushing. The results from the case studiesndemonstrated that the partitions of explosive energy estimated in this thesis assess thenblasting performance of an explosive more effectively than the energies estimated fromnthe ideal detonation codes.nnnnnnnnnnnn n The data from the case studies were also used to calibrate and validate thenfragmentation model and the blast damage model developed in this thesis. A qualitativenframework has been proposed for the selection of the most appropriate explosive andnblast design. The selection in this framework is based on matching the estimated resultsnfrom the models with the results desired from the field in an iterative process. The datanfrom the case studies were used to demonstrate the potential of the models developed innthis thesis as an explosive selection and blast optimisation tool.n