The modified drilling and blasting pattern included two rows of cut holes drilled at intermittent locations in a blasting round, i.e., two rows of cut holes were drilled after every 10–12 rows of production holes. The burden and spacing for cut holes were 0.4 and 0.5 m, respectively, and for production rows the blast geometry was 0.7–0.8 m burden and 0.9 m spacing. In the same round, rows of cut holes drilled at intermittent locations were blasted in zero delay and the production rows were detonated subsequently with 25 ms delay interval against the cut rows. The pattern worked effectively where area of blast patch in comparison to length of free face was very high (≥10 : 1). The pattern, in addition to control of flying of blasted fragments and misfire, yielded loose muck profile due to multiple collision of blast waves generated from production holes detonated in the same delay timing.
Keywords: collision of stress waves, trench method of blasting, simultaneous blasting of cut and production holes