Roof supports provide a means of temporary supporting overburden in longwall mining operations. Also referred to as powered roof supports or hydraulic chocks or shields, they are used in sets to stabilize and advance longwall systems across the face of a coal seam. In longwall mining operations the hydraulic roof supports are only used as a means to temporarily support the overburden. As the longwall system advances through the seam of coal it leaves behind and empty void referred to as a goaf. The unsupported overburden eventually collapses filling in the goaf.
- Roof support systems are adapted to specific geologic settings. They are selected on the basis of width, cutting height range, transport height, and yield capacity in order to provide a capable system that will efficiently and effectively support the load and advance the longwall system through the panel of a coal seam.
- The typical width of an individual support is either 1.75 or 2.05 meters. They are set in a line across a coal face up to 400 meters long in order to establish load balance.
The cutting height of the support is given in a range as to accommodate multiple seam thicknesses. Units may be sized to extract seams from anywhere from 0.5 meters thick to 7.5 meters thick.
The bearing force or load support by the individual chock can range in excess of 1000 tons.