Disclaimer: This article is published in the book entitled: «Flyrock in surface mining» by K. Raina.
Boulder blasting is a special application of explosive use and is different from bench blasting, as the number of free faces available is multiple. From the perspective of flyrock, the blasted fragments can be projected in all directions and hence pose a severe risk to the objects of concern. There are two main methods that are deployed in breaking the boulders:
Plaster-shooting
This technique is also known as mud capping. In this method, the explosive in cartridge or other form is just placed on the oversize rock or even covered with mud and exploded. This generally fragments the rock, if it is not too hard, and the explosive quantity is less for the size of the boulder being blasted. However, there are least possibilities of flyrock in such cases as gases escape directly into the open and dissipate fast due to lack of confinement.
Pop-shooting
It is also called block holing or boulder busting. In this method, a small-diameter hole is drilled in the oversize rock and explosive is placed within the hole and detonated, hence fragmenting the rock block into smaller pieces. However, the process presents an ideal case for flyrock that can shoot several hundred metres (Bhagat et al., 2021), depending upon the quantity of the explosive used for blasting. Other attributes of such flyrock are like what is being discussed in this work. Little literature is available on flyrock emanating from boulder blasting. In one such study (Bhagat et al., 2021), 61 boulders from a site of Konkan Railways (India) were monitored while being blasted. The data of flyrock was analysed using multiple linear regression (MLR) and classification and regression trees (CART) techniques.
It is evident that pop-shooting presents a typical case of least confinement with potential to generate flyrock.
Reference
Bhagat, N. K., Rana, A., Mishra, A. K., Singh, M. M., Singh, A., & Singh, P. K. (2021). Prediction of fly-rock during boulder blasting on infrastructure slopes using CART technique. Geomatics, Natural Hazards and Risk, 12(1), 1715–1740. https://doi.org/10.1080/19475705.2021.1944917
