A massive, self-advancing hydraulic roof support used primarily in longwall coal mining. The shield consists of a heavy steel canopy pressed against the roof by large hydraulic cylinders, protecting the shearer and the miners working below. As the cutting machine removes a slice of coal, the shields automatically lower, step forward, and reset against the newly exposed roof, allowing the unsupported rock behind them to collapse into the goaf.
We lost hydraulic pressure on shield forty-two, so the canopy is starting to bleed down under the roof load.
Also heard as
- chock
- powered roof support
Related terms
Longwall
An underground coal mining method that extracts a wide panel in a single continuous slice.
Coalface
The advancing boundary of a coal seam that is actively being mined.
Goaf
The empty or caved space left behind in an underground mine after extraction.
Roof
The layer of rock located immediately above an underground excavation or mineral seam.