Abstract
Cast blasting is commonly used in Australian dragline strip mines to minimise the amount of material handled by draglines. Cast blasts are designed with relatively high powder factors to 'cast' or displace a significant proportion of the overburden into its final dump location in the previous strip. Each additional cubic metre of material cast by explosive energy saves the cost of it being excavated and transported by the dragline. However, the extra explosive energy used increases the risk of damaging the underlying coal seam. Such damage will lead to reduced coal recovery and may negate the economic benefit derived from casting.
The Julius Kruttschnitt Mineral Research Centre has undertaken a project to understand and quantify the role of cast blasting in coal damage. As a part of this project a blast monitoring program was undertaken at the Mount Thorley mine in New South Wales. Experiments were undertaken to quantify the effect of stand-off (the distance that the explosive is kept above the coal seam) and the use of an overburden buffer or buttress placed against the exposed edge of the coal to prevent its lateral movement during blasting. A 2D dynamic finite difference numerical model was used to study the impact of different blast designs on coal movement, damage and loss.
A careful survey of coal recovery was conducted in the test areas and an economic analysis was prepared in conjunction with mine staff. The results indicate that appropriate design and careful implementation of blasting operations can have a very significant impact on the overall economics of the mine.