gob up

To gob up means to deliberately fill an excavated or worked-out area underground with waste rock, tailings, or other mined material. In coal mining especially, this practice manages the vast tonnages of spoil produced during extraction and stabilizes the cavity left behind once coal or ore is removed. The waste material, called gob or gob pack, is simply pushed or loaded into the void.

The reasons for gobbinig up are both economic and structural. Leaving large voids in a mine creates subsidence risk: the ground above can collapse unpredictably, damaging surface infrastructure or opening sinkholes. Filling the space with coarse waste rock or colliery spoil prevents sudden settlement and extends the life of accessible seams nearby. It also reduces the volume of waste that must be hauled to surface stockpiles, cutting handling and transport costs.

The material used to gob up varies by mine type and location. In coal mining, coarse slack and run-of-mine spoil work well; in metal mining, broken ore waste and waste rock from development work are common. The waste is seldom compacted deliberately. Instead, gravity and the pressure of overlying rock do most of the consolidation over time.

Gobbinig up is standard practice in longwall mining, where the extracted panel is allowed to collapse slowly behind the powered supports as the face advances, and waste from roadway development is packed into the goaf. In room-and-pillar mines, pillars are designed so the gob remains stable even when packed, although some operations deliberately weaken pillars near exhausted areas to encourage controlled collapse and reduce hanging wall risk.

The term gob itself comes from Old English and mining slang for a pit mouth or chasm. In British collieries, the gob has long been the working face of coal removal and the void behind it. Gobbinig up is therefore a direct, literal description: filling the gob. In modern practice, selective gobbinig may be used to support specific pillars or to shape ventilation paths through the mine, making it a controlled rather than incidental part of mine design.