Occupational Safety and Health Innovation Awards

The Safe Working Practice of Changing Out a Raisebore ReamingHead Underground

Brief Overview of Operation

Eloise Mine, owned by Amalg Resources, is located 70km south-east of Cloncurry alongthe Landsborough Highway. Amalg Resources purchased the Eloise deposit and thesurrounding exploration tenements, from BHP in 1994. The first ore was mined in 1996.The Eloise Copper Project is an underground operation, mining approximately500,000t/annum and producing around 70,000t/annum of copper concentrate containinggold and silver credits. The mine has been operating for five years.

Eloise mine consists of several orebodies. The main Levuka and Elrose lodes have beenthe focus of mining for the past five years and are offset by a main faulting structure (theMiddle fault). For the mining operation to continue, a new development was required toaccess this offset lode known as Levuka South. The existing ventilation infrastructurewas unsuitable to ventilate this area. Additional ventilation capacity in the correctlocation was necessary and a new ventilation shaft formed part of the planneddevelopment.

A suitable design was agreed upon and work commenced on this stage of the Eloiseunderground development in May 2000.

Brief Overview of Ventilation Shaft

The ventilation shaft was established with the collaboration of various specialistcontractors. These included Major Pontil, Raise Bore Australia (RBA), TownsvilleEngineering Industries (TEI), Jetcrete, Peabody Mining Services, Piling Contractors,Nortask, Australian Mining Consultants (AMC) and Hard Rock Electrical (HRE). Allwork was supervised and coordinated by Amalg Resources staff.

Development of this shaft begun on the 20th July, 2000 with Major Pontil drilling the pilothole from the surface to the 700m Level. A total of 482.5m. An accuracy of 0.35m wasachieved. This pilot hole was subsequently reamed to 370mm accommodate the raisebore rods. A foundation pad (incorporating the shaft collar) for the raisebore rig wasconstructed and the rig set in place to ream a 3.5m diameter shaft. The Eloise deposit isoverlain with approximately 60m of cretaceous sediments. The presence of these softsediments dictated that the shaft excavation be completed in two stages. RBA reamed towithin 57m of the surface at the completed diameter of 3.5m and then lowered thereaming head to the 700mLevel and replaced it with a 660mm diameter head. Theremaining 57m section was sunk (using the 660mm diameter as a pilot) with a largediameter piling rig (supplied and operated by Piling Contractors) and lined by Jetcretewith their remotely operated shotcreting system.

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The Problem

All stages of the ventilation shaft project were broken into identifiable sections. Inassociation with the various contractors, risk assessments were conducted for the pre-sink, pilot drilling, raiseboring, reaming and lining, and fan installation. Very early inthese planning stages it was apparent that a significant risk was associated with servicingthe raisebore cutter head.

The only method of creating a safe environment for the servicing of a raisebore head is tocompletely isolate any workers or equipment from the potential fatal hazards of fallingrocks down the shaft.

Recently the use of an oxy acetylene lance had been adopted to cut through the drill stringwith the operation of the lance being conducted from a distance of at least 3m from shaftbrow. With the drill string cut it is possible to remove the head from the shaft for service.

After the rods have been lanced the rod string then must be withdrawn to the surface, thecut stabilizer removed, a new stabilizer fitted and then the rod string reinstated in thehole. For the Eloise vent shaft project this procedure would realistically take the best partof a week to complete. At least one such event as described was required at Eloise withothers possible dependant upon cutter wear. The costs associated with this method aresubstantial and the risk of potential delay to the project was an issue. A furthercomplication involved the imminent extinction of the stabilizer rods, which at the timewere becoming an endangered species.

In short the practice of using an oxy acetylene lance to slice the stabilizer (the rod abovethe raisebore head) is an expensive, time consuming solution to the problem, which witha little lateral thinking could be resolved in a more effective manner.

The Solution

Planning at Eloise was for at least one raisebore head replacement and, possibly severalservices if cutter wear warranted changing any raise bore cutters.

Eloise Management and Raisebore Australia personnel discussed this problem and asolution was settled upon. It was decided that Eloise would undertake to design andfabricate an extended pair of breakout spanners to enable the raisebore head to beremoved without personnel being exposed to the hazards identified in the risk assessment.The concept allowed for the spanners to be placed using an underground forklift, thuseliminating the need for any person to be within 3m of the shaft brow.

The breakout spanners work in such a way that the jaw of the wrap-around spanner locksaround the ribs of the stabilizer. The second spanner – a conventional spanner is placedon the spanner flats of the stem rod. Once the jaws of the wrap-around spanner contour

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themselves around the ribs a tight fit is achieved. With the spanners installed in thecorrect position, a rod connecting the ends of both spanners is fitted, along with a“portapower” ram. The ram is extended, forcing the two spanners together applying ananti-clockwise movement to the joint. The greater the force exerted between the wrap-around spanner and conventional spanner the tighter the grip of the wrap-around spannerbecomes. The force applied is sufficient to overcome the torque applied when initiallytensioning the rods. The joint between the stem rod and the stabilizer rod is loosened.With this joint loose it is a simple matter to rotate the drill string in an anti-clockwisedirection and remove the reaming head. The reaming head is removed from the shaftusing a remote loader.

Figure 1 Wrap-around (breakout) spanner around section of stabilizer rod.

Concept drawings were completed on site and then forwarded to Amalg’s mechanicalengineer who performed strength of material calculations and provided several optionsdependant upon the availability of materials.

The next problem was to find a fabricator. After initial consultation with TownsvilleEngineering Industries preliminary shop drawings of the breakout spanners weredeveloped. As the ideas flowed modifications to these designs were implemented. TEIconsulted with Raisebore Australia to confirm the forces that would be acting upon thespanners. It was determined that the spanners would be constructed of Bisalloy 80, 50mm thick, with additional reinforcement around the jaws of the spanners. The wrap-around spanner would be 3.85m in length and the conventional spanner 4.1m in length –possibly the biggest spanners to hit North West Queensland! Due to the size of thesespanners and the relatively close tolerances required for the system to operate correctly, asection of an old stabilizer rod was sent by RBA to Townsville Engineering Industries fortesting. This allowed the system to be checked to ensure that it would work effectivelybefore its arrival to site. The “oversize” spanners arrived to site in time for the changeout.

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The raisebore cutters did not require service or replacement during the course of the backreaming. Once the shaft was reamed to within 57m of the surface at the finisheddimension of 3.5m diameter, reaming was suspended and the raisebore head was loweredto the 700mlevel to replace it with the 660mm reaming head.

Several days before changing over the raisebore head a detailed risk assessment wasconducted with all the workers that would be carrying out work, both on the surface andat the 700mlevel.

On the day of the change out everybody was briefed as to the job at hand and a JSAconducted, agreed upon and signed off by all working parties

The procedure was as follows:1. Establish communications between rig operator on surface and operators underground2. Lower rods to the floor 3. Forklift hooks up the conventional spanner4. Rotate rods and spanner around to the right hand wall (allowing sufficient room for

the “portapower” and wrap-around spanner to be fitted)5. Forklift hooks up second wrap-around spanner6. Link two spanners together with connecting rod and “portapower” ram7. Apply pressure via “portapower” to loose the rods8. Spanners removed9. After disconnecting rods, the stem rod and reaming head ere removed from the rod

string10. Raisebore head is dragged out with loader.11. Connect 660mm raisebore head

The breakout spanners and the work procedures performed as was hoped and the exerciseto remove the 3.5m diameter reaming head and replace it with the 660mm diameter headwas completed in around 2.5hours. No personnel were exposed to the dangers of fallingrocks in the shaft and a delay to the overall project of around five days was avoided. Aswith any new work plan or system areas of improvement were apparent and should theneed ever arise to create a mark two version these improvements would be incorporated.

The Benefits and Applicability for Industry

There are several benefits from this operation for the industry as a whole. It has beendemonstrated that this system is an effective method that can be used to allow safeservicing and replacement of raise bore reaming heads. The Eloise application is not apeculiar situation. This system has application both nationally and internationally. Thissystem provides a safe, economical, and timely solution to a common problem.

What previously could have been a dangerous and expensive procedure can now beconducted with a minimum of people and equipment: a forklift and operator, a spotterand an operator for the Raisebore rig (on the surface).

The spanners where passed over to Raisebore Australia at the completion of the shaft atEloise. Since using the spanners at Eloise RBA have successfully used this systemelsewhere. RBA used this system at BHP Cannington where again the system operated

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safely and effectively. Some modifications have been made to the spanners in response tothe lessons learned at Eloise. Doubtless further experience and use will promote othermodifications.

Cost

An overall cost summary showing the various alternatives that could have been usedfollows:

Alternative 1 – Construct breakout spanners to break stabilizer rod from raise bore head.Changeout 3.5m raisebore head with the 660mm reaming head.Alternative 2 – Cut stabilizer rod with oxy-acetylene. After being cut, drill string wouldhave to be brought to the surface fitted with a new stabilizing rod and sent back down thehole to attach 660mm reaming head (At least 5 days standby).

Alternative 1 Alternative 2Spanners $11,124 -

Delay Rates ($350/hr) $875 $42,000

Replacement Stabilizer rod - $15,000

Time to complete (hrs) 2.5 120

Total Cost $11,999 $57,000

*Note The spanners were available at the completion of the project. Sold to RBA at costTable 1 Cost Alternatives

Alternative 1 was chosen. This alternative was the lowest cost. This alternative offeredpotential time savings. Early completion of the shaft project was seen to be advantageous.

The whole operation ran smoothly and at completion was under budget and finishedahead of time. The result proves that innovations such as this can be implemented if alittle thought goes into the initial design stages.

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Figure 2 pulling the two spanners together

Figure 4 spanners set up at the workshop

Figure 5 breakout underway note spectators Figure 6 wrap-around spanner in place

Figure 3 view of conventional spanner in place