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Rise and fall of shortwall mining

TO THOSE who have joined the industry in the last couple of decades, shortwall mining may seem like a bit of an anomaly, while for other seasoned veterans it begs the question of where the method has gone and if it is primed for a return. Coal USA Magazine talked to underground expert Syd Peng about shortwall mining's history and future.

Donna Schmidt

Published in the March 2008 Coal USA Magazine

Shortwall began in Australia in the late 1950s with timber supports that evolved by the latter part of the next decade to hydraulic roof supports. In addition to four-leg chocks, four- to six-leg frame supports with 500-800 ton capacity were often used in shortwall.

It was not employed in the US until 1973, and in the 1970s and 1980s existed as a hybrid mining method.

"[It combined] the best features of both longwall mining and room and pillar mining," Peng explained.

Used in this system were longwall chocks for roof support, a continuous miner for coal cutting, and shuttle cars for coal transportation.

Over time, the definition of shortwall became synonymous with something else.

"In recent years ‘shortwall’ to most people probably refers to longwalls, the panel width of which is narrow, say 300 to 400 feet wide," Peng said.

A shortwall panel layout mirrored that of a longwall, he said, with chocks at the time designed with a short canopy and smaller capacity. Every cut from the CM ranged from about 8-10ft and required two cycles of chock advance, which Peng noted was a cumbersome process.

"Due to a large web cut by the continuous miner, as compared to even today’s maximum longwall web width of 44 inches, and low chock capacity, roof falls at the face were the biggest [source of] concern and problems."

The logistics of the continuous mining method, including a wait for shuttle cars to load to continue cutting, ultimately excluded the method as wider panels were developed and longwall faces became more prevalent.

Shortwalling's popularity peaked between about 1977 and 1980, at the same time as the growing interest in longwall. It was quickly abandoned in the early 1980s, with the last shortwall idling around 1987 – primarily due to innovations.

"The introduction and quick rise of shortwall, again just like longwall, was due mainly to the oil embargo and energy crisis in the mid-1970s and the nation’s desire to develop coal to reduce dependence on foreign oil," Peng said.

"Many new coal mines were developed then and new mining methods were introduced to increase production."

He also noted that in the last 30 years, longwall mining has proven that frame and chock supports are not ideal for mining requiring full extraction, as their low capacity compared to a large web size did not bode well for weak roof, a condition still common in the central Appalachian region.

"In addition, the lack of continuous haulage highly restricted the production. These two reasons accounted for its quick demise," he said.

Peng said that while no shortwalls are currently active in the US, a re-emerging prevalence of thin seams paired with technological innovations have led many to feel the shortwall mining method could potentially be poised for a comeback.

"I have heard stories about that. In fact, there are old-timers in the industry who believe that advanced equipment produced in recent years can cure the old problems associated with shortwall mining.

"I agree wholeheartedly," Peng said. "Today’s longwall shields can easily be adapted to shortwall mining and be successful [and] the proven continuous haulage systems should make shortwall mining system a truly 'continuous' mining system."

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