A fragmentation modelling framework for underground ring blasting applications

Empirical approaches for predicting fragmentation from blasting continue to play a significant role in the mining industry in spite of a number of inherent limitations associated with such methods. These methods can be successfully applied provided the users understand or recognize their limitations. Arguably, the most successful empirical based fragmentation models have been those applicable to surface blasting (e.g., Kuz-Ram/Kuznetsov based models). With widespread adoption of fragmentation assessment technologies in underground operations, an opportunity has arisen to extend and further develop these type approaches to underground production blasting. This paper discusses the development of a new fragmentation modelling framework for underground ring blasting applications. The approach is based on the back-analysis of geotechnical, blasting and fragmentation data gathered at the Ridgeway sub level caving (SLC) operation in conjunction with experiences from a number of surface blasting operations. The basis of the model are, relating a peak particle velocity (PPV) breakage threshold to a breakage uniformity index; modelling of the coarse end of the size distribution with the Rosin-Rammler distribution; and modelling the generation of fines with a newly developed approach that allows the prediction of the volume of crushing around blastholes. Preliminary validations of the proposed model have shown encouraging results. Further testing and validation of the proposed model framework continues and the approach is currently being incorporated into an underground blast design and analysis software to facilitate its application

Implementation of leading practice in geotechnical and blasting performance evaluations and the Centinela sulphide mine

The Centinela sulphide mine (formerly known as Esperanza Mine) is an open pit sulphide deposit located in Chile's Antofagasta Region, 1350 km North of Santiago. One of the strategic objectives of the mine is to implement productivity improvement projects that can be monitored, adequately quantified and adhere to strict geotechnical requirements. This paper describes the implementation of leading practices to evaluate geotechnical and blasting performance. An approach based on direct measurements was developed and implemented at the mine site. The process involved measurements of near-field accelerations and gas penetration behind pre-split-lines; run of mine (ROM) fragmentation analysis and geotechnical evaluations based on the reconciliation of key geotechnical design parameters, such as bench face angle, berm width, inter-ramp angles and final slope characteristics. A geotechnical evaluation matrix was introduced to rank final results at each monitored location. From a geotechnical perspective, the best results were obtained with some of the lowest powder factor blasts monitored. Fragmentation assessment results showed that plant requirements were still being achieved at these lower powder factors. This helped confirm that in the rock mass domains of interest, reduced powder factors in production rows were more appropriate in order to maintain higher standards of quality in wall control practices

An alternative approach to determine the Holmberg-Persson constants for modelling near field peak particle velocity attenuation

A new approach to determine the Holmberg and Persson site specific constants (K and α) for modelling near field peak particle velocity (PPV) attenuation due to blasting is presented. Currently the Holmberg-Persson approach requires the measurement of peak particle velocity at several locations resulting from a known explosive source. The objective is the determination of the attenuation characteristics of the rock mass in a specified direction and for a given explosive type. The new alternative approach significantly reduces instrumentation and monitoring requirements. It uses an analytical method to predict the peak particle velocity at the point at which rock crushing ceases and combines this with a known value of PPV measured at a pre-defined location. Four case studies which include both model scale and full scale blasting conditions are used to demonstrate and validate this alternative approach

Characterising dust generation from blasting

Predicting the generation of dust from open pit mining operations is traditionally based on the use of "emission factors" that describe the mass of dust expected to be generated from individual mining and materials handling processes. These emission factors are based on field measurements from "typical" operations. Estimates of dust generation would have much greater credibility if they could be related directly to the characteristics of the rock at the particular site and the actual blast designs used. Available blast fragmentation models predict breakage down to perhaps 1 mm in size. An approach is described that utilizes laboratory crusher test results to extend the predicted size distribution from blasting down to dust sized particles

Design methodology for underground ring blasting

This paper discusses a systematic approach to underground ring design as well as a methodology for the continuous improvement of designs as conditions change. The methodology is applicable to designs for prefeasibility and feasibility stages as well as designs for currently producing mines. The proposed method still recognises the role of experiential guidelines but provides additional and novel empirical techniques to improve the first pass approximations such that they better suit the prevailing geotechnical conditions. The strength of this method is that the designer is able to assess the impact of the design in terms of the expected fragmentation and potential damage to the surrounding rock mass