What are the most effective drilling and blasting techniques for different rock types?

1 Soft rocks

Soft rocks, such as coal, shale and clay, have low compressive strength and high plasticity, meaning they can deform easily under stress and absorb energy from explosives. Therefore, drilling and blasting techniques for soft rocks should take into account the use of small-diameter drill bits and low penetration rates to avoid excessive dust generation and hole deviation. Low-density explosives with short delays create a gentle blast wave and avoid overbreak and fines production. Close spacing and burden ensure adequate fragmentation and prevent coal damage and dilution. Additionally, presplitting or smooth blasting techniques can create stable final walls and reduce ground vibrations.

2 Hard rocks

Hard rocks, such as granite, basalt and quartzite, have high compressive strength and low plasticity, making them resistant to deformation and fracturing. As such, drilling and blasting techniques for hard rocks need to take into account several factors. This includes using large-diameter drill bits and high penetration rates for efficient drilling and accurate hole alignment. In addition, high-density explosives and long delays should be employed to create a powerful blast wave and induce sufficient cracks and fractures. Moreover, wide spacing and burden can help reduce explosive consumption while optimizing the blast performance. Lastly, perimeter blasting or cushion blasting techniques should be used to protect the final walls and reduce flyrock and noise.

3 Intermediate rocks

Intermediate rocks, such as limestone, dolomite and sandstone, have moderate compressive strength and plasticity, resulting in variable behavior depending on the stress conditions and the explosive properties. Therefore, drilling and blasting techniques for intermediate rocks need to take into account factors such as using medium-diameter drill bits and moderate penetration rates to balance the drilling efficiency and accuracy; using medium-density explosives and variable delays to create a suitable blast wave and adapt to the rock heterogeneity and structure; using moderate spacing and burden to achieve adequate fragmentation and control the blast effects; and employing pre-splitting or trim blasting techniques to improve the final wall quality while minimizing environmental impacts. Ultimately, drilling and blasting techniques for different rock types are not fixed or universal, but rather depend on the specific site conditions, objectives and constraints. Consequently, it is important to conduct proper rock characterization, blast design and evaluation, as well as applying continuous improvement principles in order to optimize the drilling and blasting operations in mining engineering.

4 Here’s what else to consider

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