Thurst refers to the mass of fractured and fallen roof rock that fills the void after coal pillars have been extracted during retreat mining. As the supporting pillars are pulled, the overlying strata intentionally collapse into the empty room. This broken, compacted rubble takes on the weight of the mountain above, relieving pressure on the active working face.
Keep an eye on the pressure gauge, the thurst hasn't fully settled behind the last row of props.
Related terms
Goaf
The empty or caved space left behind in an underground mine after extraction.
Gob
The mined-out area of a coal mine or the compacted waste rock filling it.
Room and pillar
An underground mining method where material is extracted across a horizontal plane, leaving blocks of ore to support the roof.
Depillar
To extract the supporting columns of ore or coal left behind during initial mining.