Optimizing the specific charge for limestone blasting at Aruwakkalu limestone quarry

Abstract

The largest open pit limestone mine in Sri Lanka operated by Siam City Cement Lanka Limited is located at Aruwakkalu, Puttalam. The red soil overburden is directly excavated and low grade and high grade limestone layers are drilled and blasted. Specific charge plays a vital role in open pit blast design as it affects many operational costs in mining activities. An optimum specific charge with proper fragmentation not only reduces costs but also reduces undesirable effects like ground vibration, fly rock and air blast over pressure [1]. When optimizing the specific charge, it was decided to change the charging method by creating air decks and evaluate the fragmentation of the blasted material, because it was often difficult to accomplish several elements of improvement simultaneously. Fragment size directly affects the downstream operations like loading, transporting and crushing [2]. Two computer softwares, 'JKSimBlast' and 'Split-Desktop' were used to analyse fragmentation of material where the 'JKSimBlast' was used to simulate and analyze the modelled blasts while the 'Split-Desktop' was used to analyze the blasted material. The analysis of data by the software and cost analysis reveal that top column air deck charging method would save the cost of blasting by about 11% and the Specific Charge value is reduced by 19%, resulting in reasonable fragmentation and size distribution.