"Highwall Mining the Wave of the Future"

The Terex SHM highwall miner continues to improve their impressive production record.

The manager of the Trinity Coal Services Highwall Mining Operation Stewart Cox speaks from experience when it comes to highwall mining. "I'm a second generation highwall miner and my son is also in highwall mining." Cox's first exposure to highwall mining was back in 1999 with Fola Coal when they purchased the Terex SHM No. 7. "Over the years, Terex SHM's highwall miner has evolved into a high performance machine," Cox commented. "For starters, the PTM (Pushbeam Transfer Mechanism) saves a lot of time.  Also, the machine is more user-friendly; the components are better- more rugged and dependable, and it has better auger configurations."

Given these improvements, Cox has been achieving all kinds of production records. He cited one day in which the Terex SHM No. 49 produced 4,400 tons in a 12 hour shift. "We've consistently done that and more in the higher seams," he stated. "We were also able to mine 1,740 feet in a lower seam. I think that's a record for footage in a 12-hour shift. "We are currently achieving 70% reserve retrieval and doing multiple seam mining- mining up to five seams over previous pits," Cox said enthusiastically. "Highwall mining is definitely the wave of the future."

See the Terex SHM Highwall Mining System in action in our new High Definition Highwall Mining Video.

A Little Background

Now in its second generation, Terex SHM's highwall miner is a self-contained, remotely operated highwall mining system. Designed for safety, a three or four-man team can operate and maintain this highwall miner from the surface. No crewmember is ever required to go underground thus giving the operator a clear view of the operation. This provides a very safe working environment for your employees. Depending on the height of the seam being recovered, each machine can produce an average of 40,000-120,000 short tons of coal per month. In terms of coal recovery, it can extract up to 70% of the in-situ coal, while operating on contour benches - or in trench-mining applications - with a footprint narrow as 42 ft.

The Terex SHM base-frame vehicle is carried on four hydraulically powered crawler units that give 360-degree mobility and allow the machine to be positioned precisely in front of each entry, even if the highwall is irregular. Interchangeable electric cutterhead modules mine coal-seam heights ranging from 28 in to 15 ft. The cutterhead advances by sumping (pushing forward) and shearing (raising or lowering the cutterhead boom), with the sumping force being supplied by two hydraulically powered cylinders mounted on the base frame that generate 190,000 tons of force.

The sumping force is transmitted to the cutterhead by means of 20 ft-long fully enclosed pushbeams. As the cutterhead pushes into the seam, the cut coal is carried by a pair of 18 in-diameter conveying augers that run inside the pushbeams, a major advantage of this system being that any rock that falls from the entry roof lands on top of the pushbeam and cannot contaminate the coal being transported inside it. Once the cut coal has arrived back at the base frame, it is discharged either directly into waiting haulers or to a stockpile for subsequent loading out.

In addition to providing the drive transfer and transporting the cut coal, the enclosed pushbeams play one further vital role. All of the service connections from the base frame to the cutterhead - electrical power, control, water and hydraulic lines, as well as methane sensor links - are contained within an armoured cable that is automatically unwound from a large-diameter drum on the base frame as each pushbeam is added. Resting in a groove in the top of the pushbeam, the cables and hoses are completely protected from falling roof rock, and are rewound onto the drum once an entry has been mined out and the cutterhead is being recovered.

The power available on the Terex SHM base frame unit is sufficient to allow the machine to mine entries over 1,000 ft in depth. In addition, the fact that - although they are firmly secured to each other - the pushbeams have vertical flexibility at each joint means that the system can work in seams that pitch and roll, with the cutterhead following the floor and roof of the seam and the pushbeams following its path regardless of the floor conditions. Indeed, the machine's low ground-bearing pressure means that seams with soft floors can be mined as effectively as those with a hard stone base.

Superior Success

A key factor in the company's success has been its dedicated training program. Every machine sold involves a one-week training program at Terex SHM's training center, with a further two weeks' training on site after the miner has been delivered and assembled. The training includes a 40-hour simulator program that allows operators to become familiar with highwall-miner systems before setting foot on a real machine, as well as being used for refresher courses and the introduction of operational updates.

This, of course, is another facet of Terex SHM's design strategy. A major difference with other products in the coal-mining business is that its machine is 100% retrofitable with innovations, so that a customer's investment in a miner is never technically obsolete or outdated: it can always be updated with new developments.

Higher demand for electricity, and hence for coal, is providing opportunities for increased local production with innovative systems such as highwall mining, instead of traditional coal-producers becoming increasingly reliant on high-cost energy imports. This goes for all coal-producing countries. In addition, the current strong demand for steel has opened up new opportunities for metallurgical coal production, and while to date most of Terex® SHM's customers have focused on thermal coal to sell on the utility market, several have specifically purchased systems for mining high-grade met coal that sells for US$80 a ton and more.

Looking Ahead

Most importantly, Terex SHM can assist customers with financing because of highwall mining's track record as a profitable method of coal extraction. Put all these factors together, plus the company's focus on providing systems that are reliable, durable and cost-effective, and it will indeed be interesting to see just how long it takes for Terex SHM to produce its next 50 machines for the highwall mining industry.