Raise boring is a continuous, mechanical method of boring openings used for ventilation, access shafts, and ore and waste transportation for operating mines. Raise-boring techniques are also used to complete underground shafts for civil construction projects.
Raise-boring methods and how they work
- Back reaming can be used where access is available to both the top and botom of the intended shaft. Once a pilot hole has been drilled, the reaming operation can start. The reaming operation requires the rods to be lowered through the pilot hole and the reamer atached at the botom of the intended shaft. During the reaming operation the waste falls to the botom and is removed by an underground bogger.
- Flat head cuters are presented to the rock horizontally, hence fewer cuters are required to cover a rock face. Since resistance to rotation rises with the tilt and number of cuters on a raise-boring head, the combination of horizontal presentation and fewer cuters reduces the amount of torque needed to turn the head during boring. It also contributes to smoother rotation.
- Blind boring is used to bore shafts from the surface. During the construction phase the shaft remains full of water or drilling mud, which provides stability to the shaft. Cutings are removed from the shaft using reverse circulation. This method requires virtually no interface with the existing underground workings.
- Water jet-assisted boring is sometimes used in conjunction with ground freezing in bad ground, high water lows, or toxic ores such as uranium. High-pressure water jets assist in cuting the ground.
