Blast hole drilling is a process that uses explosive charges to break up rocks and earth. It’s also known as “blasting” or “explosive excavation.” Blast hole drilling is an economical way to excavate soft to medium-hard strata, such as sandstone, limestone, and other sedimentary rocks. Voids created by blast holes may be filled with concrete for roads and buildings. The technique can also be used for tunneling transportation systems (e.g., subways). Specific types of blast hole drilling include:
Rotary Blasthole Drilling: This system utilizes a drill rig with a rotary table and reaming head to drill the borehole through unconsolidated material at angles as high as 45 degrees. Rotary is the most widely used type of blast hole drilling, and it’s also sometimes known as “rotary coring.”
Bucket-Wheel Blasthole Drilling: This system utilizes a large rotating wheel with cutting teeth or buckets that removes material from the borehole to create a smooth wall. Bucket-wheel is the fastest and most productive type of rotary blast hole drilling, but it can only be used for excavating soft formations such as sandstone and limestone.
Hydraulic Blasthole Drilling: This system uses jetting nozzles at the bottom of a drill string to remove cuttings from the borehole under high pressure. Hydraulic drilling works best for drilling into hard, abrasive rocks such as granite.
Shot-Firing Blasthole Drilling: This system uses small explosive charges to break up the material surrounding the borehole. Shot-firing is typically used for blasting large volumes of rock quickly and at shallow angles. It’s often utilized for rapid excavation of big open-pit mines or tunnels where high ground pressures are expected (such as in soft soils). Blast hole drilling can be used to create both round and square holes; different sized shot holes are required to produce each shape. A typical rotary blast hole drill rig will use no smaller than 3/8″ diameter blast holes; other systems may use 1/2″ or larger charges.
The typical process used to drill blast holes involves three steps:
- Drilling – Rotary, Bucket-wheel, or Hydraulic Blasthole Drilling
- Explosives Charge Delivering (shot firing)
- Clearing (Backfilling) – in rotary, in order for the process to be repeated in the same borehole; in hydraulic and bucket wheel blasting machines, clearing is not required as they are able to clamp off the existing hole and make another cut without backfilling it up. The drilled boreholes are typically used to place explosives charges for either demolition or construction purposes.”