|Publisher||American Rock Mechanics Association||Language||English|
|Content Type||Conference Paper|
|Title||Microcomputer Simulation Of Rock Blasting To Predict Fragmentation|
|Authors||Dr. C. Dinis da Gama, DMGA - I.P.T.|
|Source||The 25th U.S. Symposium on Rock Mechanics (USRMS), June 25 - 27, 1984 , Evanston, IL|
|Copyright||1984. American Institute of Mining, Metallurgical, and Petroleum Engineers Inc. Permission to Distribute - American Rock Mechanics Association|
In order to reduce the complexity of mechanisms influencing rock fragmentation by blasting a simulation approach is proposed, using the capabilities of microcomputer interactive graphics. Situations involving cratering and bench blasting are simulated, and both jointed and intact rocks can be subjected to explosive action, taking into consideration its breakage mechanisms. Size analysis curves relating rock distribution before and after the blasts are determined and compared with field data.
Productivity in rock blasting can be measured in terms of fragmentation, and Rock Mechanics has an essential role to improve it. In practice, distinction between good and bad blasting is established upon observation of resulting breakage, which is the most important outcome of the rock excavation process that can be evaluated, and judged upon the amount of resources expended to perform this operation. By definition, optimum fragmentation is the degree of breakage that minimizes the total cost of rock processing, including the successive unit operations of drilling, blasting, loading, hauling and crushing. Despite its importance, rock fragmentation by blasting is still poorly understood by many engineers and rock mechanics experts, due to the complex mechanisms involved in this phenomenon. Several contributions to explain and to predict fragmentation by blasting have been produced by many authors; Rustan, 1983, described seven different criteria proposed by various experts, showing distinct approaches and leading to different results, as far as predicting breakage is concerned. A common aspect of those explanations is that fragmentation by blasting is considered a size reduction process in which several parameters are involved (powder factor is present in most criteria) but no relationship is established between breakage itself and the effect of detonating explosive charges within rock masses, taking into consideration the properties of these two entities and the geometric constraints of the problem. Furthermore, although everyone agrees that the presence of natural joints and other types of discontinuities in the rock mass has a significant influence on breakage, none of the criteria seems to take into account this aspect. In an attempt to quantify that influence of joints in fragmentation, Gama, 1983, proposed an application of comminution theory, incorporating data on the rock mass fracture situation, in the mathematical expressions developed to predict fragmentation by blasting. However, blasting mechanics are not yet included in the above criterion, though it seems to constitute the basics of any acceptable explanation to his question. In order to attack the problem, one should start with knowledge on the behavior of the detonation process within rocks. Many authors studied the sequence of events that happen around a borehole just after the detonation of an explosive takes place (Duvall and Atchison, 1957; Langefors and Kihlstrom, 1963; Hino, 1959; Coates, 1967, etc.). In homogeneous rock, the essential reactions can be divided in three phases, as Figure 1 represents. Phase 1 - Immediately after the detonation of the charge, an outgoing shock wave produces crushing and radial cracking around the borehole. The velocity of radial crack propagation is a fraction of the wave velocity through the rock.
|File Size||707 KB||13|