A strategic review of the Springvale colliery near Lithgow in New South Wales has changed the direction of the mine and appears to have won it a new lease on life.
The past 18 months have seen a period of restructuring which resulted in the trimming of the workforce from 250 to 184, and the April signing of a new enterprise agreement aimed at underpinning the mine’s new direction. Springvale has repositioned itself as a 1.6 million tonnes per annum operation, primarily aimed at servicing the nearby Mount Piper power station.
The rethink was an acknowledgement by joint owners Cyprus and Samsung that poor steaming coal export prospects, and the mine’s geotechnical challenges, required a shift away from production targets set at the mine’s inception.
“Once the (new) production level was set a number of the decisions with respect to the size and structure of the operation flowed directly from that,” said Springvale Coal managing director, John Pala. “The change was communicated extensively to employees over a number of months. It wasn’t a case of them turning up one Friday and being told they’ve got a month’s notice. We felt the best way forward was to give our employees ample notice, offer voluntary retrenchment and provide a variety of outplacement-type services. Regrettably we compulsorily retrenched 24 people.”
A management re-organisation also saw the introduction of a “self-sufficient team-based organisational structure”. “Step-up” provisions in the enterprise agreement allow operators, once appointed, to work either as crew leaders (deputies) or tradespersons and tradespersons to work as crew leaders (deputies). Minimum manning levels are out and there is no demarcation. These factors had changed people’s perceptions about taking time off, Pala said. In some weeks unplanned absenteeism had been as low as 1.5%. A new bonus system based on weekly assessments of development metres and absenteeism, and six-monthly assessments of moisture in product and costs, has also been implemented.
Having a fixed domestic contract has created a greater focus on cost saving, according to Pala. An example was a reduction in overtime from 24% to about 7% of hours worked.
“But we’ve achieved savings in all sorts of areas,” Pala said. “Roof support materials, couriers, yard support maintenance, fleet maintenance, aggressive tendering, belt splicing contracts, supply of soluble oil to the longwall, the list goes on. From the smallest of things to fairly substantial items.”
Springvale’s main constraints have always been geotechnical issues related to surface topography. While the northern portion of the lease is characterised by plateaus, the southern section contains “valley areas” with cliffs and steep gullies which affect mining. Several roof falls have occurred as a result of the horizontal stress generated by this strata and these, said Pala, were the main reason Springvale had not been able to fully get up to speed.
Rigorous strata control management continues to absorb substantial amounts of funding and management time and over the past two years, much work has been done by mine management and particularly Dr Ian Stone, Springvale’s technical resources manager, and his specialist team, to enhance the strata management plan.
Typical primary roadway support comprises six 2.1m AX bolts per metre, with roof mesh, and three 1.2m rib bolts, and mesh. A combination of 4m, 6m and 8m strand bolts (cable tendons) are also used, mostly in “valley” roadways and a system has been developed to install these either as point anchored bolts or as near fully encapsulated bolts using resin cartridges, colloquially referred to as “spinbolts”
Key features of this installation system are the setting times of resin cartridges, which impact on installation and pre-tensioning, and the use of roof bolters with hollow spindle drill heads.
“A further key to the effectiveness of the spinbolt system has been the pre-tensioning of the bolts to apply a level of confinement into the roof strata,” Dr Stone said.
Much work has been done in conjunction with various manufacturers such as ANI and Cram (Joy Mining Machinery) to improve tensioning devices, making possible fairly significant advances in a short time frame. “Twelve months ago we had plus-20 kg tensioner units which the guys would have to manually hold up to the roof,” Pala said. “They would do 8-10 tendons and the things would fail. We’ve had a number of OEMs working on improving these tensioning systems to the point where we’ve now got systems as light as 12kg which operate off the continuous miner’s hydraulic system pressure. You can’t go down to the local hardware store and say, give me a tensioner I can fit onto my miner.”
The reduction to a 12kg load was partly possible because roof movement monitoring and computer modelling led to the amount of pre-tension applied to the bolts being cut from 20t to 10t.
The most recent development is a system of post-grouting the 8m tendons to improve bolt encapsulation.
“We intend to reduce to one stage the normal two stage process of mining the roadway and installing the 8m resin encapsulated spinbolts,” Dr Stone said. “The process is based on installing a point-anchored, pre-tensioned 8m tendon, designed by Jennmar, during the development cycle and post-grouting, without a breather tube, using a grout mix developed by MBT.
“The potential time saving in areas with such intensively bolted development cycles may be 40% of the cycle time.”
Despite some onerous strata control measures — “valley” areas constitute about 40% of the mine and take up 75% of development time — management appear to be getting on top of the problems. While there is nothing record-breaking about a development shift achieving 12m of advance, a different picture emerges when you realise 40 4m-pre-tensioned tendons, full rib support and six 2.1 bolts each development metre, were installed.