Mining Rule of Thumb

The primary usage of Rules of Thumb should be in the development of conceptual designs and feasibility studies or, when a quick decision is required in the solution of an operating problem. Although an approximated answer, derived from a Rule of Thumb may solve an immediate problem, Rules of Thumb are not a substitute for the application of sound engineering and design methodologies. Although we firmly believe that the presented Rules of Thumb provide great continuing value to our industry, McIntosh Engineering does not guarantee their validity, nor do we (or the referenced individual sources) accept responsibility for application of the Rules of Thumb by others. Where possible, direct quotes have been provided from individual references; however, it is possible that referenced sources may not have directly stated the Rule of Thumb for which they are assigned credit. Although we have endeavored to accurately quote all individual references contained in the Rules of Thumb compilation, we apologize in advance for any misquotes that may be attributed to individual sources. We will provide updates to the Rules of Thumb compilation, as we become aware of corrections that may be necessary.

Field: Shaft Sinking

Area: Bucket

• For sinking a vertical shaft, the bucket size should be at least big enough to fill six for each foot of shaft to be sunk; five is better. Marshall Hamilton
• For the bucket to remain stable when detached on the shaft bottom, its height should not exceed its diameter by more than 50%. Jim Redpath
• Tall buckets can be used safely if the clam is used to dig a hole in the muck pile for the buckets. Bill Shaver
• A bucket should not be higher than 7½ feet for filling with a standard Cryderman clam (which has an 11-foot stroke). Bert Trenfield
• A bucket should not be higher than 6 feet when mucking with a 630, which has a 6-foot-6-inch discharge height. Alan Provost
• You can load a tall bucket using a 630 if you slope the muck pile so that the bucket sits at an angle from the vertical position. Fern Larose
• In a wet shaft, the contractor should be able to bail up to 10 buckets of water per shift without impeding his advance. Paddy Harrison

Area: Circular Shaft

• The minimum (finished) diameter of a circular shaft for bottom mucking with a 630-crawler loader is 18 feet. Tom Goodell
• For a circular concrete shaft, the minimum clearance between the sinking stage and the shaft walls is 10 inches. Henry Lavigne
• A circular concrete lined shaft sunk in good ground will have an average overbreak of 10 inches or more, irrespective of the minimum concrete thickness. Jim Redpath
• For a rope guide system in a shaft being sunk to a moderate depth, the minimum clearance between a conveyance (bucket and crosshead) and a fixed obstruction is 12 inches and to another bucket is 24 inches. At the shaft collar, the clearance to a fixed obstruction may be reduced to 6 inches due to slowdown, or less with the use of fairleads or skid plates. In a deep shaft, 18-24 inches is required to clear a fixed obstruction and 30-36 inches is required between buckets, depending on the actual hoisting speed. These clearances assume that the shaft stage hangs free and the guide ropes are fully tensioned when hoisting buckets. Various
• When hoisting at speeds approaching 3,000 fpm (15m/s) on a rope guide system, the bonnet of the crosshead should be grilled instead of being constructed of steel plate to minimize aerodynamic sway. Morris Medd
• The maximum rate at which ready-mix concrete will be poured down a 6-inch diameter slick line is 60 cubic yards per hour. Marshall Hamilton

Area: Compressed Air

• One thousand cfm of compressed air is needed to blow the bench with a two-inch blowpipe. Bill Shaver
• Twelve hundred cfm of compressed air is needed to operate a standard Cryderman clam properly. Bill Shaver

Area: Hoist

• The hoist required for shaft sinking needs approximately 30% more horsepower than for skipping the same payload at the same line speed. Jack de la Vergne
• Without slowing the rate of advance, a single drum hoist is satisfactory to sink to a depth of 1,500 feet at five buckets per foot, 2,000 feet at four buckets per foot, and 2,500 feet at 3½ buckets per foot. For deeper shafts, a double drum hoist is required to keep up with the shaft mucker. Jack de la Vergne

Area: Schedule

• From time of award to the start of sinking a timber shaft will be approximately five months. A circular concrete shaft may take three months longer unless the shaft collar and headframe are completed in advance. Tom Anderson
• The average rate of advance for shaft sinking will be two-thirds of the advance in the best month (the one everyone talks about). Jim Redpath

Area: Shaft Stations

• The minimum station depth at a development level to be cut during shaft sinking is 50 feet. Tom Goodell
• A shaft station will not be cut faster than 2,000 cubic feet per day with slusher mucking. It may be cut at an average rate of 3,500 cubic feet per day with an LHD mucking unit. Jim Redpath

Area: Timber Shaft

• For a timber shaft, the minimum clearance to the wall rock outside wall plates and end plates should be 6 inches; the average will be 14 inches in good ground. Alan Provost
• For a timber shaft that encounters squeezing ground, the minimum clearance outside wall plates and end plates should be 12 inches. Dan Hinich
• For a timber shaft, the blocking should not be longer than two feet without being pinned with rock bolts to the wall rock. Jim Redpath

Area: Water Pressure

• For any shaft, the water pressure reducing valves should be installed every 250 feet. "Toilet tank" reducers are more reliable than valves and may be spread further apart. Peter van Schaayk
• Water pressure reducing valves may be eliminated for shaft sinking if the water line is slotted and the drill water is fed in batch quantities. Allan Widlake and Jannie Mostert