How does auger mining remove coal from a hillside?

Auger mining is a method used to recover coal from horizontal or slightly pitched seams that have been exposed by contour strip-mining or geologic erosion.12

The process functions similarly to a carpenter’s drill bit:32

• Drilling: A large, rotating cutting head bores into the exposed coal seam at the base of a highwall.13
• Extraction: As the auger rotates, it penetrates the coal, and the helical design of the auger stems carries the coal cuttings back out of the hole to the surface, where they are collected for transport.3
• Depth: As the cutting head advances, additional auger stems are attached, allowing the machine to reach depths often exceeding 60 to 100 metres.32
• Structural Integrity: To support the overlying rock (overburden), webs of intact coal must be left between adjacent holes, as well as coal above and below each hole.3

Because this method requires leaving significant amounts of coal behind to maintain structural stability, recovery rates are generally limited. Additionally, the practice is associated with environmental concerns, including water pollution and subsidence.32