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Draglines (And Specific Survey Control)

Draglines are essentially a large stripping shovel/excavator. They are also referred to as large crane-like machines. Draglines have the ability to walk slowly (generally using 'shoes' which lift the machine while moving it's tub) and are generally used in strip-mining operations to move large volumes of overburden from a pit to a spoil pile directly adjacent or behind the machine.

Draglines have proven their worth over time as they have been in use since before World War 1 and modern versions are fundamentally the same. There are many draglines still in use that are over 20-30 years old.

They use a bucket to excavate material which is suspended from a large boom using wire ropes. Draglines require a lot of energy to operate and are therefore usually fed by a 6.6kV electrical cable.

Dragline Photos:

For more information specifically about draglines, click here.

Draglines - Survey Duties

Dragline Survey Control

Surveyors provide control for draglines in the following forms:

- Chop Line Pegs
Because strips are often wider than the length of a dragline boom, the dragline operator needs to take multiple passes to remove the material above the coal. The first part of the dig sequence is to dig a 'key'. The chop line pegs tell the operator where the farthest the dragline can sit while being able to remove material up to the high wall (see example #1 and example #4 below).

- Ramp Edge Pegs
Ramp edge pegs are used to tell the dragline operator where they need to dig to create a ramp suitable for trucks to haul coal out of the pit. See example #3 for an example of a ramp dug by a dragline (after grading, ramp maintenance and hauling has commenced). Dump trucks are usually designed to work efficiently up to a certain grade of ramp; if a ramp is too steep it could increase hauling costs and maintenance required on trucks. Surveyors are responsible for ensuring the ramp grade is controlled while it is being excavated to ensure that it will be to an appropriate standard.

- Low-wall Crest Pegs
Low wall crest pegs are used to show the dragline operator where the crest of the low wall is required to ensure that the coal at the bottom will be uncovered using a pre-defined batter angle (see example #1 and #2 below).

- Low-wall Toe and Coal-edge Pegs
Once the dragline is getting closer to the coal surface and if access permits, low wall toe and coal edge pegs are used to show the dragline operator where the low wall needs to stop at the bottom as well as where the coal edge should be (see example #2 and example #5).

- High-wall Block Markers
High-wall block markers allow the dragline operator to determine their approximate position at anytime and reference themselves spatially to an engineering plan.

There are other components that may be pegged that are not listed above; however the information provided should provide a basic understanding for survey machine control operations regarding draglines.
As part of a monthly pickup, surveyors are also required to conduct a survey of the materials removed by a dragline (see volume calculation section), survey the roof and floor of the coal as it is uncovered and excavated, survey the coal edge exposed to compare with previous data and survey the coal in the highwall once coaling has completed in that area.

Example #1: Dragline pegging example before coal is uncovered

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Note: The coal edge pegs in this example are for reference only. They would not be placed at this stage of the dig.

Example #2: Dragline pegging example after coal is uncovered

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Example #3: Photo of a ramp dug by a dragline

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Example #4: Photo example of Chop Line Pegs

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Example #5: Photo example of Coal Edge Pegs

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The position of coal edge is determined using progressive surveys of the coal as mining operations continue (see coal reconciliation section). The photo above shows the coal edge pegs with what seams to be excess coal on the left of them. This is often the case due to either coal being mixed with overburden resulting from a blast or excavation operations, or by a slight shift in the position of the coal from forces exerted during blasts. These pegs are useful for guiding the dragline as to what needs to be uncovered as it progresses. The photo below shows how the coal face can be seen more clearly when it has been cleaned up by an excavator.

Example #6: Photo of Coal Edge once uncovered by dragline (and cleaned by an excavator)

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