Abstract

Efficient blasting practices yield controlled rock breakage, minimize dilution, ensure safe ground control conditions, and minimize the environmental footprint of the mining cycle. The direct and indirect cost benefits of optimizing blast methods on mine sites promote continuous technical and technological improvements in our understanding of both thermochemical notions of explosives, and mechanical response of rock during blasting events. Research and development initiatives investigate the parametric influence of geomechanical features, and geometric configurations on blast results. Past contributions in these fields have led to industrially acknowledged guidelines and rules of thumbs to provide blast engineers and operators with procedural frameworks to design blast patterns. Such methods aim to provide generic perspective of the expected blasting behavior, and often require site specific testing and characterization work to achieve optimal design. Onsite iterative full blast trials remain a major component of blast design optimization. These time consuming and inefficient testing programs involve a large number of variables. Such work can benefit from cost effective blastability indexing through systematic Single Hole Blast (SHB) testing.  The present work highlights recent developments and practical applications for SHB indexing in different geological settings.

Blastability indexing with SHB tests involves a series of individual shots blasted parallel or sub-parallel to an open face. The distance from the free face (i.e. burden) is varied between the tests to obtain burden dependent characteristic trends. Blasts are performed using typical equipment and material used onsite to test operational and geomechanical conditions in place. Topographical mapping of the resulting craters is obtained from remote sensing surveys (LiDAR and photogrammetry in this work). The craters are described incrementally along the blasthole length to capture superficial variations of the original blasting surface. The breakout shape perpendicular to the face is represented by a power law equation capable of describing prismatic, concave and convex cratering. The burden dependent power law formulation comprises two site specific parameters which effectively describe the blasting behavior considering operational and geomechanical conditions tested. These parameters serve as blastability index to assess blasting performance and derive site specific design guidelines.

This study presents SHB tests performed in hard rocks, soft rocks, and composite materials. SHB craters were surveyed using LiDAR and photogrammetry to obtain three-dimensional point clouds. SHB indexing is performed by describing the obtained test results through the crater power law characteristic parameters. The reported trends are analyzed with respect to the type of geology tested. The shape of the crater (prismatic, concave, convex) highlights the different cratering mechanisms active during SHB tests. A geomechanical concept map of the predominant cratering mechanism is postulated from the observed test results. Results at the tested sites are derived into a series of burden relationship and blast design guidelines to highlight the applications of SHB indexing.