1936 Illustration 1; Schema representing the crack growth mechanism of a presplit (Tose, 2006). MODELS USED The formulism used for the calculation of presplit spacing is shown in equation 1. The basic development of the procedure was elaborated by Sanden (1974) and published in his M.S. thesis prepared under the direction of Dr. Peter Calder at Queen's University. The theoretical portion of this thesis was published and modified by Chiappetta (1982) in "Pres-splitting Theory and Applications" and in "Perimeter Blasting". J≤2∗VÄ∗tLÉS+Sv (1) Where: S = Hole Spacing (m) Ro = Presplit drill radius (m) Pb = Blasting Pressure in Hole (Mpa) T = Intact Rock Tensile Strength (Mpa) The application of this criterion has been widely used within the mining industry, and the only input parameter of rock characterization is the tensile strength of intact rock, without considering the condition of rock mass, so its best results are shown when the quality of the rock mass has a quality of good to very good, in terms of RMR89 60% to 80% (Bienniaswki: 1989). However, for rock masses with high fracturing rates, in practice a theoretical spacing value is entered, and adjusted according to the results observed on the slope, after blasting. 2. THEORETICAL BASIS OF NUMERICAL MODELING WITH ELFEN PROGRAM FEA MODEL To generate fragmentation in rock, it is necessary to work with an MBM (Mechanistic Blasting Model), which is an explicit model where the codes of finite and discrete elements are coupled. This code has evolved from the work of Munjiza (Munjiza, 1992). The rock mass is generated by a mesh of first-order tetrahedral finite elements since these can be easily adapted to any geometry and have less computational cost for calculations. If we consider that the CFD and DEM models work in tandem, this type of triangular element is the most accepted to reduce calculation times. The boundary conditions of the system are obtained from the CFD model, which are entered into the program as a variable load over time. This produces a pressure on the elements that form the wall of the study blasthole.
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