No one disputes that West Virginia is coal country. Lying in the centre of the eastern US Appalachian coal field, the state has long been host to both surface and underground coal production, and while today’s industry is concentrated in a few specific areas, historical minesites abound. Where these have involved contour mining in the past, sandstone highwall outcrops often mark the only trace of previous activity, the rock faces standing proud within the surrounding forests that are such a feature of the rugged mountain landscape here.

Since the passing of the Surface Mining Control and Reclamation Act (SMRCA) in 1977, the requirements placed on mining companies relating to the restoration of mined-out land have changed dramatically. In particular, the need is for much better restoration practice than was typically applied in the past, such that the outcrop that marks the top of the highwall is now much less intrusive in the landscape.

However, while “pre-law” highwalls (those created before the SMRCA came into force) remain the focus of ongoing restoration by both the federal and state agencies, current regulations permit companies to rework the residual coal resources, opening up a major market opportunity for highwall-mining systems.

With a new operation located on steep valley hillsides about 10 miles south of the state capital, Charleston, Parkstone Energy is one of the companies that has grasped this opportunity with both hands.

Parkstone has been working at its Siata mine since the middle of 2005, and now has not one but two Superior highwall miners in operation there.

Parkstone president Shannon Keeran explained the sequence of events that led to the decision to select SHM machines for this specific job.

“You have to have the right application for this type of system,” he said, “and we have miles and miles of pre-law highwall on our properties. Within about 60 miles, Parkstone Energy has a number of underground and conventional surface operations, and our acquisition of this property has added highwall mining to our production portfolio.

“As well as that we have the luxury that the Siata mine is less than four miles by truck to our wash plant, which in turn is a mile from the dock [on the Kanawha River] where we load our coal onto barges for direct shipment to our customers.

“With diesel prices the way they are now, that makes a big difference in terms of our transport costs.”

A four-seam resource

Parkstone is now producing coal from a four-seam sequence, contained within the Upper Carboniferous Kanawha Formation, close to the geological hinge between the state’s Northern and Southern coal fields. Of the four seams, resources in the lower three are contained in pre-law benches; only for the top seam is Parkstone having to produce coal first in order to open up a new bench on which its highwall miner can operate.

Nonetheless, as Keeran noted, merely re-opening the old benches can present some challenges in terms of ground clearance. “After clearcutting the regrowth timber on the benches,” he said, “we clean down to the old bench level using an excavator. One of the operational battles we have is keeping enough bench open ahead of the SHM machines.”

Another operational constraint is imposed by the narrowness of the existing pre-law benches. Keeran said Parkstone has to live with the bench widths used by the company that mined here initially although, as always, challenges such as this can present opportunities for technical solutions.

“We helped SHM to develop its new return conveyor system, which takes cut coal from the rear of the miner back to the centre of the bench,” he said.

“That way, we have much more flexibility for our stockpile and loader operation there.”

The top, previously unmined seam, the Upper Coalburg, averages around 40 inches in thickness, and is separated from the Lower Coalburg below by around 50 feet of sandstone and shale interburden. A further 35ft of waste separates the 40-42in Lower Coalburg from the underlying Winifrede seam, which here averages around 38in thick.

The bottom seam in the sequence, the Chilton Rider, lies 30ft below this, but is thicker than the others, averaging 46-48in. All four lie well within the operating range of SHM’s low-seam cutterhead module, which is fitted to both the highwall miners onsite.

Deeper into the wall

Parkstone’s first SHM unit came onsite in July 2005.

The acquisition of additional resource blocks later

in the year more than doubled the mine’s reserves, and this, together with the buoyant coal market led to the company placing an order with SHM for a second machine. This was delivered in March 2006.

Both miners feature SHM’s rear discharge configuration which, as the company’s director of engineering Stewart Myers explains, has been a key to increasing the machine’s production capability.

“Moving from the original vertical-discharge design to rear discharge, and then introducing the right-angle conveyor concept to take cut coal from there to the stockpile, was a major advance,” he said.

“Now we have taken the idea a stage further with the second right-angle conveyor, bringing the coal back to the centre of the bench without the potential for any bottlenecking at the transfer points.”

Parkstone has scheduled its production such that the first machine is dedicated to mining in the upper two seams – the Coalburgs – while the newer unit works in the Winifrede and Chilton Rider seams below.

Each machine moves from bench to bench in sequence, with a new stretch of one bench being prepared while mining is taking place on the other. That way, as Keeran explained, the two operations can be managed properly without either getting too far ahead or behind the mine’s production requirements.

Operating on the top seam involves stripping waste back to a new highwall, then loading out the seam to leave a working bench for the miner.

Waste stripped from the top bench is backfilled for restoration there, and is also used for reclamation on the lower benches. Since it is a new (rather than reworking) operation, Parkstone is able to create a wider bench for the Upper Coalburg seam, at around 100ft, whereas the pre-law benches below are narrower, ranging from 60-80ft wide.

Hence the incentive to develop the return-conveyor system, Keeran noted.

While the full operating depth of the current generation of SHM miners is...click here to read on.