In pillar and stall workings, miners first
created a passageway straight into the heart of the coal seam.
Once the seam was accessed, miners created rooms by removing
coal from a sizeable underground area, but were careful to leave
large tracks of coal behind. The untouched coal would act as
pillars that supported the roof of the mine and prevented
cave-ins as the miners cut deeper into the seam.
Through this method, miners created a
honeycomb of rooms and pillars that were occasionally bisected
by long haulage tunnels. The extent of these tunnels depended on
the furthest reaches of seam, and were often several kilometres
long. Once miners removed coal from the farthest extent
they could reach, they would then backtrack. Since pillar
coal was easily accessible, miners would then rob the coal from
the pillars. Workers took extensive care when removing this
coal since pillar subtraction weakened the roof structure and
room would eventually cave in.
To prevent cave-in accidents, tunnels also
required timbers as pit props, which supported the rocks and
prevented smaller debris from falling onto the miners.