Excavation Methods

FUNDAMENTALS


access to seam from surface
	Excavation Methods
		Drifts/Inclined Shafts/Declines

Excavation methods for drifts are likely to be the same whether straight or with a change of direction. There are 3 methods which have been used:

Conventional drill, blast and muck-out. There would be variations in equipment used, often from contractors' preference or equipment availability, and also dependent on the grades involved, but the basic drill, blast and muck-out process is the same in all cases
Use of "roadheading" machines (machines with a cutter head designed to cut stone rather than coal) to excavate the material instead of drilling and blasting. This gives a more continuous process and should give a good drift profile. The use is limited by the grades involved (maximum 1:4) and the hardness of the material to be cut (maximum 60-80 MPa UCS).
Use of a tunnel boring machine. Provides a good, circular profile which is good for stability and ventilation but usually requires a false floor to be laid to create a flat floor for travel (ie involves removal of stone and replacement with concrete or some such material, a wasteful process. Nevertheless, this infill section can be utilized to install services, particularly waste water handling). Limited by grades involved and grade control can be problematic is some strata conditions. Not suitable for other than very gradual changes of direction (typically minimum 500m turning radius although tighter radius machines can be designed and utilized). Unlike drill and blast or roadheading methods, tunnel boring machines do not have the capability to readily vary the dimension of the excavation nor are they suitable in varying ground conditions.

Herrenknecht AG – suppliers of tunnel boring machines (info in German)