FUNDAMENTALS

access to seam from surface

 

Excavation Methods

   

Vertical Shafts

 

Excavation Methods

Vertical Shafts

There are 4 methods in general use:

  • Conventional drill, blast & remove stone ("muck out") to surface with a winder. If the shaft is to be "lined" (i.e. sides to be covered with a concrete or even a steel lining), this is normally placed as the shaft is excavated.

  • Drill a pilot borehole from surface to existing underground workings, ream to a large diameter, then drill and blast and muck-out through the borehole, the stone being removed from below using the mine's haulage system. Again the shaft can be lined as excavation proceeds.

  • Raise boring – again a pilot hole is drilled and in this case reamed out to the full shaft diameter by a large reaming bit pulled upwards from the bottom of the shaft. Again the stone has to be removed from below using the mine's haulage system. With this method, installing any support or lining in the shaft is difficult until excavation is completed, so the method is only suitable in ground able to stand unsupported, at least for a period. The method is most commonly used to provide small diameter ventilation shafts which are required for relatively short periods (and therefore can be left unlined).

  • Blind boring – a shaft is excavated using normal drilling techniques with a very large diameter bit. Drilling muds would normally be used to remove the cut stone and to support the side walls (permanent support could be difficult to install until excavation is completed). Large amounts of water would be required and direction control could be a problem. This is not a commonly used method.

The first and last of the above methods should have minimal effects on any existing operations. For the other two methods, the mine must be developed to the shaft location and the mine's haulage system must be able to handle the excavated material either separately from the coal stream or by separating the material in the coal preparation plant. In rare cases it may be possible to dispose of the material in old workings underground.

Abergeldie shaft boring – commercial website for contracting company

Alimak Raise Climbers – can be used for vertical shafts as well