Shaft Sinking

SAFEFASTEFFICIENT

SHAFTSINKING

P F +61 8 9535 7999M PO Box 1454 Mandurah WA 6210E [email protected] www.craigsmining.com.au

Tullamarine Holdings Pty LtdABN 50 009 455 930

PATENT PENDING Australian Standard Patent Application Number 2004293489

EXECUTIVE SUMMARY

A Safer, More Efficient Method of Shaft Sinking.

A new way of sinking circular shafts with continuous steel lining has been developed by Craigs Mining Services and successfully used in both the Northern Territory and New South Wales.

The method utilises purpose-built telescoping steel cylinders which are welded together to provide a continuous smooth shaft lining with excellent airflow characteristics, ideal for ventilation shafts. The finished lining is also waterproof, a significant benefit compared to conventional concrete-lined shafts.

Safety is greatly improved particularly in poor ground conditions, as exposure to unstable openings can be minimised by lowering liners in the shaft as excavation proceeds.

Enhanced sinking rates of up to 3 metres a shift can be achieved with a crew of three. This results in substantial cost savings compared to traditional shaft sinking methods. As the liners have successively slightly smaller diameters, they can be stacked inside each other or “nested” for transport, which further reduces project costs.

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PATENT PENDING Australian Standard Patent Application Number 2004293489

EXECUTIVE SUMMARY

A Safer, More Efficient Method of Shaft Sinking.

A new way of sinking circular shafts with continuous steel lining has been developed by Craigs Mining Services and successfully used in the Northern Territory (Chariot Gold Mine), New South Wales (Inverell Diamond Exploration Shaft) and Western Australia (Forrestania Flying Fox Nickel Mine)

The method utilises purpose-built telescoping steel cylinders which are welded together to provide a continuous smooth shaft lining with excellent airflow characteristics, ideal for ventilation shafts. The finished lining is also waterproof, a significant benefit compared to conventional concrete-lined shafts.

Safety is greatly improved particularly in poor ground conditions, as exposure to unstable openings can be minimised by lowering liners in the shaft as excavation proceeds.

Enhanced sinking rates of up to 3 metres a shift can be achieved with a crew of three. This results in substantial cost savings compared to traditional shaft sinking methods. As the liners have successively slightly smaller diameters, they can be stacked inside each other or “nested” for transport, which further reduces project costs.

SHAFT SINKING

1. INTRODUCTION

Prior to commencing site works, engineering design is carried out to ensure that the steel liners are of appropriate thickness for the planned shaft diameter, depth and ground conditions. To date, liners of up to 3.0m diameter and 6.0m length have been used to depths of 80 metres.

All Craigs Mining equipment has current certification as required by Department of Industry and Resources WA, including vacuum ore lifts, mobile headframes, hoists, kibbles, ropes, shackles and associated mining gear.

2. SHAFT COLLAR

The agreed shaft location is levelled and a safe working area is established. A vertical shaft pilot hole is drilled and back-filled with clean sand. If required, dewatering bores are drilled and equipped and the necessary extraction and discharge licences are applied for.

As shown on Figure 1, the shaft (10) is excavated by jack pick or drill and blast methods and the mullock removed by backhoe or excavator. The top steel liner (12) has four suspension

points and is lowered into the excavation by crane.

It is levelled and secured at the base by concrete fill for at least one quarter of its length (16).

Clean sand fill is introduced behind the liner (18) from the concrete at the base, to about one metre below ground level.

The collar is then concreted in place (20) and incorporates a removable shaft plug (14) which is used to support the sinking headframe over the shaft opening.

A concrete apron extends from the collar (20, also see following photos) to allow the headframe to be wheeled on and off the shaft and the plug removed for installation of additional liners as the shaft is deepened.

3. SECOND LINER

The headframe is rolled back over the installed shaft plug and the tyres are deflated to lower the frame to the concrete surface. Mining continues as before, with mullock removal by vacuum orelift until the shaft is deep enough for installation of the second liner (Figures 2, 3).

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Tullamarine Holdings Pty LtdABN 50 009 455 9301. INTRODUCTION

Prior to commencing site works, engineering design is carried out to ensure that the steel liners are of appropriate thickness for the planned shaft diameter, depth and ground conditions. To date, liners of up to 3.0m diameter and 6.0m length have been used to depths of 80 metres.

All Craigs Mining equipment has current certification as required by Department of Mines and Petroleum WA, including vacuum ore lifts, mobile headframes, hoists, kibbles, ropes, shackles and associated mining gear.

Figure 2 (left) shows the headframe (24) wheeled back over the plug (14), which is sitting in the recess (22) in the collar. Mining is continuing to extend the shaft depth.

The headframe is equipped with two hoists, one for man riding and one for lowering the liners.

Figure 3 (below) shows the headframe moved off from the shaft, after re-inflating the tyres. The plug is removed from the recess in the collar.

The second liner is then suspended from the crane (30) and lowered into the shaft.

Each successive liner is slightly smaller in diameter than the preceding one, allowing them to pass down the shaft through the previously installed lining.

The clearance gap between upper liner interior and lower liner exterior is ideally about 10mm, or

20mm difference in diameter.

Note that the top of the second liner has been slotted with regular cuts.

These allow it to be belled out to the same diameter as the previous liner and to be welded securely to it.

If ground conditions are poor, the second liner can be introduced into the shaft and lowered as excavation progresses, using the headframe hoist to lower it (Figure 6).

This maximises safety by preventing exposure to unsupported walls which may otherwise collapse.

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Figure 4 (left) illustrates how the second liner, after being lowered by the crane, is hung within the shaft from the four suspension points of the top liner.

The plug is then re-installed in the top of the shaft and the crane is removed (Figure 5, left).

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The headframe is then wheeled back over the shaft and plug, and the tyres are deflated.

The slings by which the second liner is suspended from the top liner are attached to the hoist rope of the headframe, and the new liner is lowered into position ready to be joined to the shaft collar. (Figure 6, left)

As an alternative, the liner can be lowered into its final position by the crane rather than the headframe hoist.

Figure 7 shows the second liner installed and joined securely by welding to the base of the top liner.

The top of the second liner which has multiple slits is jacked out until its diameter matches that of the top liner.

Both the join and all the cuts are then welded, to provide a secure and waterproof seam.

A stable platform for welding is provided by temporarily filling the lower part of the shaft with clean sand, which is removed by vacuum orelift once welding is complete.

Ventilation during welding is provided by the vacuum sucker pipe, which is positioned below the work position and just above the floor.

Concrete backfill (34) is introduced behind the base of the liner, through

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temporary slots which are then welded closed. Depending on ground conditions, the collar is at least one quarter the liner height. The void (36) may be completely filled with concrete if required for reinforcement and stability.

4. SUBSEQUENT LINERS

The shaft is continued to design depth by continuing using the same methodology of excavation and liner installation (Figure 8).

Once the shaft has been completed, pre-fabricated modular shaft furniture can be lowered and welded into position. An example of furniture designed and supplied for a previous job is shown in Appendix I, together with other engineering drawings.

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Shaft and headframe arrangement showing safety railing, collar, plug recess and plug (to right). Note tyres on headframe are inflated for moving headframe off shaft.

Shaft close-up, showing one of four suspension points in top liner; headframe moved off shaft

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View of shaft from headframe, showing plug (part) at top

Headframe wheeled back over shaft, with tyres deflated

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Headframe in position over shaft, with vacuum orelift in place. Note clean sand in foreground

Plug and crane preparing to reinstall into shaft collar


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TWIN SHAFTS & CMS SINKING CUT FLYING FOX COSTS

Lateral thinking and Craigs Mining Services’ innovative shaft sinking techniques significantly cut the cost of ventilation upgrades at Forrestania’s Flying Fox Mine.

Faced with the task of increasing primary ventilation from 140 to 220 cubic metres per second, conventional wisdom dictated a 4.5-metre diameter vertical shaft some 50 metres deep. CMS’ solution was to install two parallel shafts of smaller diameter.

Ventilation consultants determined that two 2.7-metre diameter shafts would allow the required volume of air and, after reviewing costs and feasibility, Flying Fox Mine Underground Manager, Duncan Sutherland, gave CMS the go-ahead.

“By adopting Craigs’ proposal we brought the shaft installation project in at around half the cost of conventional methods,” Mr Sutherland said, “but there are other advantages as well.”

The twin ventilation system effectively operate independently, and with one shaft offering similar flow to the original system, there are potential operating costs, maintenance, and mine safety benefits.

“Using Craig’s system, sinking two shafts didn’t take any longer than sinking one big shaft by conventional methods,” Mr Sutherland said, “and because there’s no exposure to the rock wall it’s probably inherently safer too.

“I would be happy to discuss this with anybody considering a similar project.”

FORRESTANIA FLYING FOX MINE VENTILATION SHAFTS PROJECT


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Shaft Sinking

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