Open Cut » Drilling & Blasting
The objective of the ACARP C23028 Improved Blast Outcomes project was to develop a methodology for drill and blast engineers to improve blast safety and performance by more accurately accounting for rock mass structure in their blast designs. This work involved integration of the blast energy and fragmentation technology and expertise developed at the SMI with the structural mapping and modelling technology and expertise developed at the CSIRO. This project would deliver:
· Improved prediction and management of blast related hazards, such as face-bursts; and
· Improved blast-induced fragmentation through better blast design based on more accurate representation of rock mass structures in blast analysis software.
For the assessment of blast design efficiency and identification of potential hazards such as face bursts, a multi-criteria approach has been adopted. The tool developed in this project allows the practitioner to take into account several aspects of blast design and performance:
· Face burden;
· Energy intensity prediction (a function of face burden, explosive energy and timing);
· Structural connectivity;
· Fracture intensity and
· Domain index.
The face burden metric incorporates the location of the front row of the design in relation to the surveyed topography of the highwall.
The energy intensity calculation uses topography of the highwall and calculates the blast energy at this location using the elemental charge approach developed at the SMI. This approach takes into account the distance of actual location from the explosive charge, explosive energy intensity ant the detonation timing of holes.
The structural connectivity examines the connection pathways between rock mass defects identified in the structural data and the blast design.
The fracture intensity (total fracture length per area) can also be included in this analysis.
Finally, a domain index can be provided by the user to characterise rock mass properties not captured in the above criteria.
The tool allows the user to perform the multi-criteria evaluation using the above and a 'colour map' visualisation is generated. Regions identified in this map with either high or low values can be interpreted within the context of the analysis as representing energy intensity or potential for face-burst that may result in air blast and / or fly rock.
Another function of this tool is to provide an improved estimate of blast induced fragmentation based on in-situ size distribution, energy intensity and breakage characteristics of the rock mass. The in-situ size distribution can be estimated by the tool using the structural mappings. This estimation involves calculation of both the volumetric joint count and, if sufficient data is available, the polyhedral volume estimation. The tool will then estimate post-blast fragmentation using this in-situ estimate and the energy at that point using a comminution based approach. This calculation can be performed on a domain by domain basis thus allowing for the consideration of different rock types and rock qualities.
The initial technology transfer component of this project is being undertaken through a series of mine site visits and demonstrations. Discussions between the two collaborating institutions have commenced on the preferred commercialisation pathway for this software.