Airway Velocity "Rules of Thumb"; More guidelines than hard and fast rules


Katie Manns, BBE Consulting Australia

The mining industry instinctively follows rule-of-thumb design velocities to determine airway sizes. Although these are important building blocks in ventilation planning it should be recognized that mines are far more complex and various, often opposing factors, are at play. Therefore, it is important that each ventilation problem be analyzed on a case-by-case basis to determine the best-fit solution for an operation. The ventilation design process should not be constrained by rules-of-thumb which in some cases could lead to unrealistic infrastructure requirements and exorbitant capital expenditure. This type of design often lacks corporate support leading to a scenario where no ventilation upgrade is implemented. Economic velocities typically consider the cost of power, development costs and operational risk. These typical rules-of-thumb work reasonably well as a starting off point when considering feasibility of greenfield projects. For established mines that are looking at expansion these rules may no longer apply due to capital expenditure constraints or geotechnical ground conditions. The theoretical optimum should be reviewed in the case of an established mine where infrastructure could perhaps be maximized. For example, the geotechnical risk of large diameter raises at depth may require multiple small diameter raise to maintain the theoretical economic velocity. If a mine has a life of less than 5 years, then the cost of power is an insignificant proportion of the total owning cost. For these mines, operating the ventilation raises at an increased velocity to avoid a complicated and expensive capital upgrade might be the more appropriate option, even though it opposes the traditional rules-of-thumb. Mines which are capital constrained may be better off accepting a higher operating cost for the interim or settle for minor infrastructure upgrades rather than run the risk of the entire ventilation upgrade not being approved at all. This paper explores a case study of a deep Australian mechanized mine extending from 1500m to 2200m depth with limiting ground conditions where velocities higher than the economic norm would be applicable.