Methods of Underground Coal Mining
HER: High Extraction Retreat
A disadvantage of most room-and-pillar
methods is that so much coal is left behind in
the pillars. So miners must have been thinking,
"Suppose we just left little "stumps" or "fenders"
instead of whole pillars; we could get a really
high rate of extraction and then
make a hasty retreat before the whole thing
High-extraction retreat mining is a form of
room-and-pillar mining that extracts most of the coal.
Rooms and pillars are developed in the panels,
and the pillars are then systematically removed.
Rows of chain pillars are along the panel boundaries,
as is the case in longwall mining.
Panels are 400-600
feet wide, and extraction ranges
from 70 to 90%.