A comparative investigation of inter-row delay timing vis-à-vis some rock properties on high sandstone benches

The inter-row delay timing plays a pivotal role in any blast round as it not only influences the mechanism of fragmentation, but also offers a vast potential in improving the overall results of fragmentation. It is in this perspective that the current study presents a comparative investigation of the influence of inter-row delay timing on fragmentation in two different strength sandstone formation in large-scale, multi-row blast rounds of a two surface coal mines in India. The investigations are based on full-scale field blasts. The study highlights the role of p-wave velocity and brittleness vis-à-vis impedance to shock wave propagation during the initial as well as final stages of rock breakage. Given this, the role of shattering effect (in stronger sandstone formations) and heaving effect in weaker strength sandstone has been clearly established in the rock breakage mechanism. Furthermore, the study also suggests that for weaker sandstone, longer inter-row delay timing (15-25 ms/m of effective burden) yields the best fragment size results. Similarly, for stronger sandstone formation, shorter inter-row delay timing (10-17.85 ms/m of effective burden) yields the best fragment size results.