Occupational Safety and Health Innovation Awards
The Safe Working Practice of Changing Out a Raisebore Reaming Head Underground
Brief Overview of Operation
Eloise Mine, owned by Amalg Resources, is located 70km south-east of Cloncurry along the Landsborough Highway. Amalg Resources purchased the Eloise deposit and the surrounding exploration tenements, from BHP in 1994. The first ore was mined in 1996. The Eloise Copper Project is an underground operation, mining approximately 500,000t/annum and producing around 70,000t/annum of copper concentrate containing gold and silver credits. The mine has been operating for five years.
Eloise mine consists of several orebodies. The main Levuka and Elrose lodes have been the focus of mining for the past five years and are offset by a main faulting structure (the Middle fault). For the mining operation to continue, a new development was required to access this offset lode known as Levuka South. The existing ventilation infrastructure was unsuitable to ventilate this area. Additional ventilation capacity in the correct location was necessary and a new ventilation shaft formed part of the planned development.
A suitable design was agreed upon and work commenced on this stage of the Eloise underground development in May 2000.
Brief Overview of Ventilation Shaft
The ventilation shaft was established with the collaboration of various specialist contractors. These included Major Pontil, Raise Bore Australia (RBA), Townsville Engineering Industries (TEI), Jetcrete, Peabody Mining Services, Piling Contractors, Nortask, Australian Mining Consultants (AMC) and Hard Rock Electrical (HRE). All work was supervised and coordinated by Amalg Resources staff.
Development of this shaft begun on the 20th July, 2000 with Major Pontil drilling the pilot hole from the surface to the 700m Level. A total of 482.5m. An accuracy of 0.35m was achieved. This pilot hole was subsequently reamed to 370mm accommodate the raise bore rods. A foundation pad (incorporating the shaft collar) for the raisebore rig was constructed and the rig set in place to ream a 3.5m diameter shaft. The Eloise deposit is overlain with approximately 60m of cretaceous sediments. The presence of these soft sediments dictated that the shaft excavation be completed in two stages. RBA reamed to within 57m of the surface at the completed diameter of 3.5m and then lowered the reaming head to the 700mLevel and replaced it with a 660mm diameter head. The remaining 57m section was sunk (using the 660mm diameter as a pilot) with a large diameter piling rig (supplied and operated by Piling Contractors) and lined by Jetcrete with their remotely operated shotcreting system.
The Problem
All stages of the ventilation shaft project were broken into identifiable sections. In association with the various contractors, risk assessments were conducted for the pre-sink, pilot drilling, raiseboring, reaming and lining, and fan installation. Very early in these planning stages it was apparent that a significant risk was associated with servicing the raisebore cutter head.
The only method of creating a safe environment for the servicing of a raisebore head is to completely isolate any workers or equipment from the potential fatal hazards of falling rocks down the shaft.
Recently the use of an oxy acetylene lance had been adopted to cut through the drill string with the operation of the lance being conducted from a distance of at least 3m from shaft brow. 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, the cut stabilizer removed, a new stabilizer fitted and then the rod string reinstated in the hole. For the Eloise vent shaft project this procedure would realistically take the best part of a week to complete. At least one such event as described was required at Eloise with others possible dependant upon cutter wear. The costs associated with this method are substantial and the risk of potential delay to the project was an issue. A further complication involved the imminent extinction of the stabilizer rods, which at the time were becoming an endangered species.
In short the practice of using an oxy acetylene lance to slice the stabilizer (the rod above the raisebore head) is an expensive, time consuming solution to the problem, which with a 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 several services if cutter wear warranted changing any raise bore cutters.
Eloise Management and Raisebore Australia personnel discussed this problem and a solution was settled upon. It was decided that Eloise would undertake to design and fabricate an extended pair of breakout spanners to enable the raisebore head to be removed 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, thus eliminating 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 locks around the ribs of the stabilizer. The second spanner – a conventional spanner is placed on the spanner flats of the stem rod. Once the jaws of the wrap-around spanner contour themselves around the ribs a tight fit is achieved. With the spanners installed in the correct 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 an anti-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 spanner becomes. The force applied is sufficient to overcome the torque applied when initially tensioning 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-clockwise direction and remove the reaming head. The reaming head is removed from the shaft using 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 mechanical engineer who performed strength of material calculations and provided several options dependant upon the availability of materials.
The next problem was to find a fabricator. After initial consultation with Townsville Engineering Industries preliminary shop drawings of the breakout spanners were developed. As the ideas flowed modifications to these designs were implemented. TEI consulted with Raisebore Australia to confirm the forces that would be acting upon the spanners. It was determined that the spanners would be constructed of Bisalloy 80, 50 mm 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 these spanners and the relatively close tolerances required for the system to operate correctly, a section of an old stabilizer rod was sent by RBA to Townsville Engineering Industries for testing. This allowed the system to be checked to ensure that it would work effectively before its arrival to site. The “oversize” spanners arrived to site in time for the changeout.
The raisebore cutters did not require service or replacement during the course of the back reaming. Once the shaft was reamed to within 57m of the surface at the finished dimension of 3.5m diameter, reaming was suspended and the raisebore head was lowered to the 700mlevel to replace it with the 660mm reaming head.
Several days before changing over the raisebore head a detailed risk assessment was conducted with all the workers that would be carrying out work, both on the surface and at the 700mlevel.
On the day of the change out everybody was briefed as to the job at hand and a JSA conducted, agreed upon and signed off by all working parties
The procedure was as follows:
1. Establish communications between rig operator on surface and operators underground
2. Lower rods to the floor
3. Forklift hooks up the conventional spanner
4. 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 spanner
6. Link two spanners together with connecting rod and “portapower” ram
7. Apply pressure via “portapower” to loose the rods
8. Spanners removed
9. After disconnecting rods, the stem rod and reaming head ere removed from the rod string
10. 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 exercise to remove the 3.5m diameter reaming head and replace it with the 660mm diameter head was completed in around 2.5hours. No personnel were exposed to the dangers of falling rocks in the shaft and a delay to the overall project of around five days was avoided. As with any new work plan or system areas of improvement were apparent and should the need 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 been demonstrated that this system is an effective method that can be used to allow safe servicing and replacement of raise bore reaming heads. The Eloise application is not a peculiar situation. This system has application both nationally and internationally. This system provides a safe, economical, and timely solution to a common problem.
What previously could have been a dangerous and expensive procedure can now be conducted with a minimum of people and equipment: a forklift and operator, a spotter and an operator for the Raisebore rig (on the surface).
The spanners where passed over to Raisebore Australia at the completion of the shaft at Eloise. Since using the spanners at Eloise RBA have successfully used this system elsewhere. RBA used this system at BHP Cannington where again the system operated safely and effectively. Some modifications have been made to the spanners in response to the lessons learned at Eloise. Doubtless further experience and use will promote other modifications.
Cost
An overall cost summary showing the various alternatives that could have been used follows:
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 would have to be brought to the surface fitted with a new stabilizing rod and sent back down the hole 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 cost
Table 1 Cost Alternatives
Alternative 1 was chosen. This alternative was the lowest cost. This alternative offered potential 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 finished ahead of time. The result proves that innovations such as this can be implemented if a little thought goes into the initial design stages.
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