A Numerical Analysis of the Presplitting Controlled Blasting Method

Sharafisafa, M. (Amirkabir University of Technology) | Mortazavi, A. (Amirkabir University of Technology)

OnePetro 

Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. The less competent the rock mass itself is, the more care has to be taken in avoiding damage. Presplitting is one of the most common methods which is used in many open pit mining and surface blast design. The purpose of presplitting is to form a fracture plane across which the radial cracks from the production blast cannot travel. Presplitting should be thought of as a protective measure to keep the final wall from being damaged by the production blasting. The purpose of this study is to investigate of effect of presplitting on the generation of a smooth wall in a rock domain under a surface blast process. The 2D distinct element code was used for simulation of presplitting in a rock slope. The blast load history as a function of time applied to the inner wall of each blasthole. Important parameters that were considered in the analysis were stress tensor and fracturing pattern. The blast loading magnitude and blasthole spacing were found to be very significant in the final results.



INTRODUCTION

Drilling and blasting continues to be an important method of block production and block splitting. Drill and blast technique has a disadvantage that sometimes it produces cracks in uncontrolled manner and also produces micro cracks in the block as well as in remaining rock, if not carefully carried out. Recovery by this method is low as compared to other methods. Therefore, attempts have been made to develop controlled growth of crack in the desired direction. The control of fractures in undamaged brittle materials is of considerable interest in several practical applications including rock fragmentation and overbreak control in mining [1–3]. One way of achieving controlled crack growth along specific directions and inhibit growth along other directions is to generate stress concentrations along those preferred directions. Several researchers have suggested a number of methods for achieving fracture plane control by means of blasting. Fourney et al. [4] suggested a blasting method which utilizes a ligamented split-tube charge holder. Nakagawa et al. [5] examined the effectiveness of the guide hole technique by model experiments using acrylic resin plates and concrete blocks having a charge hole and circular guide holes. Katsuyama et al. [6] suggested a controlled blasting method using a sleeve with slits in a borehole. Mohanty [7,8] suggested a fracture plane control technique using satellite holes on either side of the central pressurized hole, and demonstrated its use through laboratory experiments and field trials in rock. Nakamura et al. [9] suggested a new blasting method for achieving crack control by utilizing a charge holder with two-wedge-shaped air cavities. Nakamura [10] performed model experiments to examine the effectiveness of the guide hole with notches. Cho et al. [11] performed experiments using a notched charge hole to visualize fracturing and gas flow due to detonation ofexplosives