Jim Dowling - Mining Engineer

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TRACKLESS MINING AND RAMPS (DECLINES)

 

Traditional rail track bound equipment – that is, locomotives and mine cars – can only follow the track and cannot cope with steep gradients and tight curves. Steep vein stoping between tracked main levels can only be carried out from the upper level down or, more often, the lower level up. All supplies and equipment have to be manhandled up or down raises to reach any intermediate positions. Rubber tyred vehicles ("Trackless"), on the other hand, can negotiate gradients of up to 1 in 6 in ramps between main levels. These have enabled more efficient stoping systems by creating new drilling points which were previously extremely difficult to form. The same reserve blocks can still be mined from top or bottom, but now also from intermediate positions (‘sublevels’), formed between the main levels, from trackless ramps. In parallel with the growing availability of trackless vehicles, higher capacity electro-hydraulic rotary percussive and down the hole (DTH) drills have been developed. These are able to enhance the drilling of blast holes by increasing drilling speed and hole length (more power), and more accurate drilling for these longer holes (accuracy is often the factor which ultimately limits hole length). These improvements make possible the extraction of pillars between the new sublevels created with trackless machinery, with rows of blast holes c. 10–100 m long. This was the start of trackless sublevel stoping.

 

 

Stoping in steep vein mines before the introduction of trackless equipment

Stoping in steep vein mines, before the introduction of trackless equipment, could only be started from main levels, from the top downwards or, more often, the bottom up

 

 

Trackless equipment can mine on gradients up to 1 in 6, creating many more points from which to start stoping, called ‘Sub Levels’

Trackless equipment can mine on gradients up to 1 in 6, creating many more points from which to start stoping, called ‘Sub Levels’

 

 

crosscuts to the vein and strike direction

Plan view of straight and zig-zag ramps, showing crosscuts to the vein and strike direction. Note that in plan view the straight ramp is not parallel to strike direction unless the vein is vertical

 

 

Cross sections of straight, zig-zag and spiral ramps in the footwall of a steeply dipping vein showing ramp, crosscuts and sublevels

Cross sections of straight, zig-zag and spiral ramps in the footwall of a steeply dipping vein showing ramp, crosscuts and sublevels

 

 

Spiral ramp (by permission of the Wheal Jane Group)

Plan view (left) and isometric view (right) of a spiral ramp (by permission of the Wheal Jane Group)

 

 

Longitudinal sections showing a straight, zig-zag and spiral ramp with crosscuts to the vein

Longitudinal sections showing a straight, zig-zag and spiral ramp with crosscuts to the vein

 

 

Where the orebody has some degree of vertical extent, ramps (declines) are a vital part of trackless stoping. In sublevel open stoping, ramps are part of the stope. In addition ramps are found as main developments connecting different parts of the mine, used for ventilation, access, transport and so forth. At shallow trackless mines, ramps connect underground workings to the surface. There are three types of trackless ramp: Straight, Zig-Zag (Switchback) and Spiral. In a complex setting two or more of these types may be combined (see SLOS animation). The sketches show these ramps in association with trackless stoping in a steeply dipping vein. The ramps will be in the footwall to avoid subsidence damage, as close as possible to the orebody to minimise crosscut lengths, but not too close to suffer blasting damage from stoping

 

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Longitudinal section, cross section and plan view of a zig-zag ramp with level turns

Longitudinal section, cross section and plan view of a zig-zag ramp with level turns

 

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