The paper deals with the study of empirical models for the analysis of blasts-induced fragmentation. To verify the reliability of the method, the results obtained a priori through the application of the models are compared with the analyses of muck piles photos taken from a series of blasts in an open pit quarry, thanks to the Split-desktop software (Split Engineering, LLC, Tucson, USA). The study of the particle size distribution is very important when sizing an excavation site, as the average size of the pile must be compatible with the equipment used for clearing and conveyance, and with the first phase of the processing plant, i.e. primary crushing. After a description of the excavation technique in use at the quarry site, its main characteristics are outlined. The parameters used to create the empirical models refer to the geomechanical characteristics of the rock, the geometry of the blasts, the characteristics of the explosive and its interaction with the rock mass, paying attention to the correlation between initiation timing and induced fragmentation. A detailed description of some empirical models together with the Split-desktop software were therefore provided. Thanks to both data and photos of the muck-piles from the exploitation at the quarry, the particle size curves resulting from each model were compared with those obtained from the software. This allowed to validate the empirical method in a preliminary design phase.
The production cycle of an exploitation site generally develops in two phases, that of excavation and that of processing. The excavation technique depends on both the type of deposit and the geomechanical characteristics of the exploited material. In this case, the drill and blast technique will be analysed for an open pit quarry. As known, this technique involves carrying out a series of cyclical operations, consisting of: evaluation of the geometry of the blast, choice of explosives and initiation systems, charging and initiation, scaling, loading, hauling and dumping. Based on the different phases of the cycle, there are many factors that influence and are influenced by the size of the blasted material [1]. Particularly, the grain size distribution and its maximum size Dmax is important, as it represents the maximum size that the opening of the crusher jaws can accept. Therefore, the desired fragmentation is a key parameter in the design of a blast [2 – 3]; it is influenced by the drilling diameter, the blasting pattern, the type and the amount of charge used [4]. To study the fragmentation induced by a blast, the geomechanical properties of the rock mass and its response to explosives have to be considered: as a first approximation, the impedance of the "rock-explosive" pair is a parameter that allows an a priori estimation of the result of a blast in a given rock mass [5].