Systems of Approach
Variable Parameters
These are within the power of the mining design engineer. Although he can
be severely restricted when designing face and developments, the mining
design engineer will ultimately have the power to choose whatever deemed
appropriate in all these parameters:
i)
Number and Sequence of Seams Worked: The inter-relationship
between workings in adjacent seams, the future of un-worked
seams, the future of exploited seams, possibility of gas emissions
and/or water penetration, consideration of two thinly separated
seams as one and sequence of working.
ii)
Width and Length of Panels: Dictated by fixed parameters to a
large extent, but the final decision is taken by the design engineer
who has a large scope. Seam thickness, depth of workings, type,
price and availability of machines, regularity of the seams and
many other factors affect the choice.
iii)
Thickness of Extraction: Although influenced by fixed
parameters but numerous alternatives are available to mining
design engineer. Seam thickness, competence of roof and floor
strata, machinery (especially supports) available and their relative
prices, capacity of transport equipment on and outside the face
area, together with gas and dust emissions are the main factors.
iv)
Induced Fractures: Thick seam working considerations especially
in steep seams, possibility of gas emissions from adjacent strata,
danger of water inundations etc.
v)
Width and Number of Pillars Between Panels: Mainly for
reasons of support, gas transfer, subsidence etc. There could be no
pillar in rare cases in longwall mining, one pillar in the case of
traditional systems in longwall mining or many which will
resemble room and pillar mining. In room and pillar, the main
question is whether or not the pillars are to be won later.
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vi)
System of Waste Support: Many choices are available from total
filling, termed solid stowing in horizontal mining, to partial
stripping and ultimately total caving which is predominant today.
vii)
Rate of Face Advance: For highest output the maximum speed of
face advance is ideal but many constraints limit this. In room and
pillar, mainly support considerations are the limiting factor. In
longwall, face ends operations and gas and dust emission prohibit
the highest speed. Also, only theoretically at present, the speed of
pressure arch advance rate may limit the face advance rate causing
roof instability on the face.
viii) Shape and Dimension of Roads: The mining engineer has a large
scope. In room and pillar, rectangular cross sections are normal. In
longwall mining, both rectangular and arched roadways can be
chosen, depending on support and economic criteria. The main
considerations are to preserve the ground stability by means of
minimizing the energy release and to observe operational
requirements.
ix)
Direction of Extraction Relative to Dip: Purely a technical,
operational and economic parameter. Theoretically anything can be
chosen from position 0 to 90 on the horizontal plain. Availability
of machinery and their relative costs, together with operational
restrictions, are commonly the deciding factors.
x)
Method of Heading Drivage: In room and pillar method, using
the continuous miner is predominant. In longwall mining, drilling
and blasting is was conventional but using road heading machines
such as the TBM is fast becoming the obvious choice, especially in
retreating system. In the advancing system, heading drivage must
be designed in a way that it produces minimum interference with
the operating face. Keeping these at some 40-50 metres in front of
the face is the answer, but at the cost of installing and uninstalling
the supports.
xi)
Ventilation Considerations: This affects the rate of advance and
hence output, system of working etc. Generally, ventilation is more
expensive in room and pillar due to large amount of leaked air. But
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this leaked air prevents gas concentrations to occur. In longwall
mining, on the other hand, concentration of working is high and
therefore the presence of both gas and dust may constrain the face
advance rate. Ventilation system must therefore be designed
efficiently in all cases for its important impact on the production
rate.
xii)
Details of Working Method: Such as pillar extraction and exact
configuration of the rooms in room and pillar and the optimum
number and capacity of machines such as shuttle cars and
continuous miners to be applied. On a typical longwall face, the
number and the type of shearer loaders and the exact sequence of
their cutting cycle in relation to the supports have to be decided by
the mining design engineer.
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