CH 2

Development and opening
Nature of Underground Mining

Surface mining may be often preferred over underground mining for
cost and productivity reasons but attraction of underground mining
include;
• Variety of ore deposits that can be mined by the method
• Versatility of the method to meet production needs that cannot be
approached by surface mining
• Less environmental impact
Some analysts predict that the share of underground mining may
increase and argue;
• Most of the near-surface deposits have already been mined
• Great expense of meeting all environmental requirement on
surface
Other analysts for surface mining to continue to increase percentage
and argue;
• Ever increasing productivity of surface mining equipment
• Ease with which surface mining equipment can be upsized and
automated
Nevertheless it is safe to assume that underground mining will
continue to play and important roll.
Main factors characteristics in planning for development
• Less affected by location factor, especially climate
• Less environmental consequences
• Most critical factors are ore and rock strength
• Presence of ground water
• Rock temperature
• More skilled labor is required
• Financing may be more difficult due to higher risk
• Subsidence may become the most important environmental
concern
Limited excavation and relatively small opening may be required but
these could be more costly on tonnage bases and more type of
excavation could be required.
Require ventilation. Possibility of double use of development works.
Openings driven for exploration purpose may be used for
development and vice versa
Type of underground openings
Underground development openings can be ranked in three
categories in order of importance
1. Primary: Main openings, e.g., shafts, declines
2. Secondary: Level or zone openings, e.g., drift, entry
3. Tertiary: Lateral or panel opening, e.g., ramp, crosscut
Generally development work is done in this order but some
variation exist with different mining methods.
Mine Development and Design
Mine development must proceed considering all aspects of mine
design. Extreme care must be taken in decisions because of the
complexity and cost involved and the most crucial matters include
a) Mining method selection
Once underground mining method is selected then selecting the
exploitation method is the focus. Development should not proceed
until;
• Production plan is adopted
• Select the class of underground method: unsupported, supported,
or caving.
• Which depends on natural and geological conditions of the mineral
deposit
• Economical and environmental factors
The mining method determines the type and placement of primary
development opening. E.g., in caving methods the openings may
need to be placed outside the fracture boundary. If the integrity of
the ground overlaying the active mining area can be ensured primary
openings can be located centrally.
b) Production rate and Mine Life
A number of geologic and economic conditions determine the
optimum rate of production including; market conditions, selling price
of the commodity, mineral grade, development time, mining cost,
means of financing, government support, taxation policies, etc..
Generally, the higher the production rate the shorter the mine life.
The recent trend is for higher production rate and shorter mine life
due to higher borrowing cost, greater investment risk, higher labour
cost, etc.
c) Main Access Opening
These concern the number, shape, and size of main openings.
c) Main Access Opening
These concern the number, shape, and size of main
openings.
Such decisions are made during the selection of primary
material handing Factors influencing the decisions
include depth, shape, size of the deposit, topography,
natural geological conditions, mining method, and the
production rate. Changes should be avoided because
they are disruptive and expensive specially in short-lived
operations
Location of portal
Portal Location It is very important for a mine to have a reliable access
to the deposit. The type and location of the portal significantly affects
mine operation. The only way for men and machines to reach the
deposit is through them. Portals are the first to be developed and the
last to be abandoned, and therefore, they have the longest life among
other mine structures. Some of the factors that should be taken into
account during portal construction are:
- Portal should be located in strong strata. Else, the portal could be
subject to strata disturbance jeopardizing mine production.
- Portal area should be free from flooding.
- Should be as close to the center of the property as possible.
- The portal should be at the lowest elevation of the seam/orebody
so that the grades favor hauling and mine drainage. Transportation
costs are lower if coal/ore is hauled down gradient and drainage is
easier when the final destination is lower than the origin.
4. Type of opening
• Shafts that could be vertical or near vertical
• Declines
• Adits or drifts
Shafts
Shaft - A primary vertical or non-vertical opening through mine
strata that connects the surface with underground workings.
Vertical shaft are among the most common for deep mines. Near
vertical are costly.
Application of near vertical shafts: in moderately inclined deposits,
(30 - 70) degree. Application of vertical shafts: in vertical or steeply
inclined, > 70 degree deposits Shaft plant consists of the facilities
installed for materials handling ore, coal and associated waste
material and means of transport of miners. They may include
systems for ventilation, drainage, power supply, and
communication.
A three dimensional
model of an
underground mine with
shaft access
Decline or Slope
Declines can be a spiral tunnel which circles either the flank of the
deposit or circles around the deposit. The decline begins with a box
cut, which is the portal to the surface. Depending on the amount of
overburden and quality of bedrock, a galvanized steel culvert may be
required for safety purposes. They may also be started into the
wall of an open cut mine. Application: shallow or medium depth
horizontal deposits, high production low life. Limited 12% to 14%
inclination with trucks and about 16% for conveyors.
Adit or drift : for shallow outcrops, horizontal deposit or
steeply inclined in high relief
- Transportation, both inside and outside the mine, is affected by
portals. Conveyor belts, loading chutes and other elements of coal
hauling network inside the mine are planned on the basis of portal
location and size. If for some reason a portal cannot be used,
arranging for alternate routes can be very expensive. The location of
the entrance to the mine affects the trucking distance between the
mine output and the next destination for the coal/ore (coal/ore
processing plant or customer). This is especially true in hilly areas
such as the Appalachia, where a portal placed on the wrong side of
a hill adds several miles of additional transportation. Generally also,
remote location of a portal requires building a road. A
deeper/longer portal is often preferred to a shorter portal when the
shorter portal is farther away from the customer or the washing
plant or the highway
Figure . Effect of the location of the portal on transportation.
It is often found that the best conditions do not occur together. For
example, a portal location that is the closest to the customer may
have the worst strata conditions. Therefore, one must carefully
weigh all the options before deciding on the location.

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Development and opening

Nature of Underground Mining

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