Drill and blast method is one of the common tunnelling techniques in hard rock. The principle behind the blasting in tunnel is to create free face at the centre of tunnel by means of cut holes and then extending the blasting to full face of tunnel. In simple words, blasting relies on two main factors: 1. shock wave to create cracks in the rock 2. Expansion of gas to move into the cracks to crush the rock. #tunnelengineering #tunnelengineer #blasting #drillandblast #mechanizedtunnelling #blast #d