Traditionally in hard rock mining, large diameter raise boring was thought of as 3.04 m or 3.66 m diameter holes 300 m deep. Mine and ventilation engineers were challenged to design systems either incorporating such holes, or slashing and modifying to suit. Now, larger than 5 m diameter holes up to 1,000 m deep are being excavated. The ability to pilot and ream such holes not only creates new options for mine engineers in mine ventilation system design, but also creates new opportunities in mine access. By combining holes of this diameter with the ability to accurately drill long pilot holes through the entire length of the hole, borehole hoisting systems are now fully capable of being main production or service accesses for mines. Production capacity in excess of 8,000 tpd using rope guides has been successfully proven in a 5.52 m diameter raise bore 845 m deep, with a further deepening planned to 1,500 m, by Cementation at Alamos Gold’s Young-Davidson mine in Northern Ontario.
Applications can include ventilation openings; access for movement of men or materials; production hoisting; specialty civils excavations. These uses are driven by specific needs and in hard rock, it can reasonably be argued that for most applications of non-horizontal development, raise boring with perfectly cylindrical shafts and smooth walls offers a host of cost and time saving benefits over conventional development methods with faster advance rates; less disturbance of the rock structure; decreased airflow resistance; reduced labour cost; and greater safety for the operating personnel by putting them in a safer environment.