Shock Wave Interactions in Rock Blasting: the Use of Short Delays to Improve Fragmentation in Model-Scale

A series of detailed small-scale tests have been made to investigate the use of short delays to promote better fragmentation caused by shock wave interactions. The block design had a size of 650/660 x 205 x 300 mm (L x W x H) and two rows with five 10-mm blastholes in each row. The spacing (S) and burden (B) were 110 and 70 mm, respectively, giving an S/B ratio of 1.6. The results showed no distinct differences or high improvements of the fragmentation when the delays were in the time range of interactions compared with no shock wave interactions. The decrease of x (50) (mean size) was around 20 % at a delay time similar to 1.1 ms/m burden compared with longer delays like 2 ms/m. A statistical analysis of the results has been made to evaluate the minimum at short delays and it is not significant.