Brief description about the support systems used in underground cut and fill method of mining

1. SUPPORT SYSTEM
IN CUT FILL STOPING
Presented By
Vishal Kumar Das
117MN0646
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2. Introduction
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Cut And Fill Stoping
In cut-and-fill mining, the ore is removed in a series of horizontal
drifting slices. When each slice is removed, the void is filled (generally
with waste material from the mineral-processing plant), and the next
slice of ore is mined.
Backfilling provides not only a platform for mining of each slice of ore,
but also provides support to the wall rocks. It is a costly method and
therefore the ore has to have a high grade to compensate the added
cost on backfilling.

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4. Types Of Cut & Fill Mining
There are two types of cut and fill mining methods based on ore
excavation directions; overhand method and underhand method.
4Ovehand cut and fill mining

5. Cut And Fill Mining
Underhand Method
Underhand method is the method to extract the
ore deposit from the top downwards. The ore is
drilled from the shallow level and continue by
mining the deep deposits along the stope. This
method enables us to obtain the ore product from
the earlier stage. However
Overhand Method
Overhand is a method to extract the ore from
bottom upwards. Intact vein is hanging over the
stope and the lower void is filled with waste
materials. The advantage of this method is location
of backfill under the working area enable the use
of backfill material with relatively low strength to
reduce mining costs.
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6. Support
Supported methods require substantial amounts of artificial support to maintain
stability in exploitation openings, as well as systematic ground control throughout
the mine. Supported methods are used when production openings (stopes) are not
sufficiently stable to remain open during operation, but the opening required to be
held open to prevent caving or surface subsidence.
The most satisfactory forms of artificial support are backfilling/stowing,
timbers/stulls, cribs/packs, and hydraulic/frictional props.
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7. The most satisfactory forms of artificial support is backfilling/stowing
Backfilling provides not only a platform for mining of each slice of ore, but also provides
support to the wall rocks. It is a costly method and therefore the ore has to have a high
grade to compensate the added cost on backfilling.
Backfill material can be differentiated into three different categories, hydraulic fill, paste
fill, and rock fill, based on water, cement and aggregate content.
Hydraulic fills are any kind of backfill carried by water through pipelines.
Solid particles are sluiced through the water quickly without having the chance to settle
until they reach the dumping point. Paste fill is bound with cement to create a very strong
product. Much thicker than hydraulic fill, similar to toothpaste, paste fill is also much more
uniform in texture after placement.
Rock fill can be cemented or non-cemented mine waste rock or aggregate material placed
underground by means of trucks, conveyors or raises.
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9. There are a number of options available for the backfill to be used in
cut and fill mining, the choice of which is dependent on the support
requirements of the area. These options include:
• Waste fill
• Pneumatic fill
• Hydraulic fill with dilute slurry
• High-density hydraulic fill (paste fill)
The highest strength option available is paste fill, followed by sand fill,
and finally unconsolidated rock fill. Beyond the support requirements,
the fill must be able to support any equipment that is necessary for
stope development, as it will become the working floor for the next
stope.
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10. Why do we support mines?
• Keeping miners safe (safety factor).
• Ensure continuity of ore production to avoid shortage in profit.
• Finally, keeping expensive machines in the underground mines safe
(e.g. machines used in long wall mining).
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11. When do we need to support mines?
If there are weak or unconsolidated parts of rocks are present in the roof and walls of mines.
If there some geologic structures (e.g. shear zone) that weaken rocks.
If there are voids and spaces in the rocks.
If there are some clay beds that can shrink and expand due to its swelling property, and
hence sliding of rocks in presence of water can be expected.
If there are underground water that helps in chemical weathering leading to loose rocks and
corrosion of machines.
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12. Preliminary steps for designing support system:
1. Rock cores have been obtained from different boreholes at various
locations or RLs of the metalliferous mine using diamond drilling
technique
2. At the coring locations, the recovery factor and RQD of cores were
estimated.
Recovery factor is the amount (i.e. length) of recovered material divided by the
total length of the core run (presented as a percentage)
Recovery Factor =
𝑇𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑟𝑜𝑐𝑘 𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑
𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑟𝑒 𝑟𝑢𝑛 𝑙𝑒𝑛𝑔𝑡ℎ
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13. Rock Quality Designation (RQD) is a modified core recovery percentage in which the
lengths of all sound rock core pieces over 100 mm in length are summed and divided
by the length of the core run.
• Pieces of core that are not hard and sound should not be included in the RQD
evaluation
• For the RQD evaluation, lengths must be measured along the centerline of the
core
𝑅𝑄𝐷 =
𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑟𝑜𝑐𝑘 𝑝𝑖𝑒𝑐𝑒𝑠 > 100 𝑚𝑚
𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑟𝑒 𝑟𝑢𝑛 𝑙𝑒𝑛𝑔𝑡ℎ
ROCK QUALITY DESCRIPTION BASED ON RQD
RQD Value Description Of Rock Quality
0-25% Very Poor
25-50% Poor
50-75% Fair
75-90% Good
90-100% Excellent
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14. 3. Then the cores were transported to the laboratory.
In the rock mechanics laboratory , various geo-mechanical parameters, such as
compressive strength, tensile strength, elastic modulus, Poisson’s ratio, density
and other parameters have been determined.
Core samples from different boreholes of diameter approximately 36 mm and
length of 15 m were received for testing these parameters
NUMERICAL MODELLING : The Finite Element Method
This method is based on systematic computer programming and offers a scope for application to a
wide range of structural analysis. The basic concept in this approach is that a body or structure can
be divided into a finite number of smaller units of finite dimensions called ‘elements’. The original
body or structure is then considered as an assemblage of these elements connected at finite number
of joints called ‘nodes’ or ‘nodal points’. The properties of these elements are formulated and
combined to obtain the solution for the entire body or structure.
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15. The global system of equations is developed as follows:
{F} = [K]. {q}
Where,
{F} = global force vector, i.e. forces in each node,
[K] = global stiffness matrix based on material properties, and
{q} = displacement vector containing each node.
Based upon the results obtained from the above tests the most
economical as well as suitable support systems were designed as per
the underground mining conditions
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16. How do we support mines?
[It is the job of mine engineer but with consultation with the mine geologist.]
We have many options as mine support such as:
(1) Wooden logs support
(2) Support using metal rods
(3) Support using metal pins or roof bolts
(4) Support using metal fence (net)
(5) Concrete support and using brick walls
(6) Resin support
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17. Wooden Logs Support
• Wood logs (trunks) should be straight and about 4-6 m long
• Evergreen trees are recommended (e.g. pine trees)
• Iron wedges must be used to fixthe wooden logs
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19. Advantages and disadvantages of wooden logs support:
Advantages
• Cheap even when it is imported
from abroad.
• Can be cut to the desired length.
• Gives early warning when it
swallows
Disadvantages
• Wood trunks can not be reused
in other mines.
• If wood swallows, another type
of mine support should be
applied.
• Wood must be coated to avoid
corrosion by mine water, insects,
bacteria, …..etc.
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20. Support Using Metal Rods
Simply, it is a metal rod consists of two
cylinders of different diameters.
Length can be controlled using pins
and moving upward & downward
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21. Advantages and disadvantages of metal rods support:
Advantages
• Rods can be easily re-used again
(e.g. in other mine).
• Length (height) can be easily
controlled.
• Gives high support capacity.
Disadvantages
• Expensive.
• Does not give early warning like
wood trunks.
• Moisture and mine water can
cause corrosion of metal.
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22. Support Using Metal Fence (NET)
Usually used for ceilings only, especially in case of rock fall.
Metal pins are needed to fix the metal fence.
Can be used for walls also but if clay beds are missed.
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23. Advantages:
• Necessary for ceilings that have weak
fractures in hard rocks.
• Gives early warning in case of mine collapse.
• Reasonable support capacity.
• Collect falling rocks.
Advantages and disadvantages of metal fence support:
Disadvantages:
• Expensive.
• Not suitable for soft rocks
• Moisture and mine water can
cause corrosion of metal.
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24. Support Using Metal Pins or Roof Bolts
Usually used for ceilings only.
A 1-1.5 m hole is needed, with 1.4 cm diameter.
Bolts and pins must have ribs for good support.
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25. Advantages and disadvantages of metal rods support:
Advantages
Necessary for ceilings that have
weak fractures in hard rocks.
High support capacity.
Disadvantages
Expensive.
Not suitable for soft rocks
Moisture and mine water can
cause corrosion of metal.
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26. Concrete Support And Using Brick Wall
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27. Concrete support and using brick wall used for walls with clay beds, or
when the bedrock is friable and brittle.
Concrete can bear more stress than bricks.
Advantages:
• Necessary for friable and clayey bedrocks.
• Perfect support capacity.
Disadvantages:
• Relatively expensive.
• Can not be easily modified or removed.
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28. Resin Support
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29. Resin Support used for friable and porous ceilings and walls.
An organic stuff (polymers) is used for injection.
Advantages:
Ideal for friable and porous bedrocks.
Injection is an easy job and not environmentally harmful.
Disadvantages:
Relatively expensive.
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30. Special type of support:
(Uncommon)
Metal Bars & plates
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31. CASE STUDY : PONGKOR UNDERGROUND GOLD MINE
[SUPPORT SYSTEM OF PONGKOR UNDERGROUND MINE ]
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32. The support system in Pongkor underground
gold mine is constructed based on RMR rock
mass classification. The roadway and cross-cut
access have standard dimension as 4m in width
and 4m in height with a flat roof whereas the
stope dimension follows the vein width. The
main access of Pongkor underground gold mine
from surface to the ore location in subsurface
connected by roadway as ramp up and
developed in footwall side.
The support requirement in Pongkor roadway
consists of two types support requirements,
standard support system using H-beam and
standard support system using shotcrete.
The H-beam has been applied since 1994 when
the mining started their excavation, while the
shotcrete has just been applied on 2010. A few
years ago, shotcrete is not recommended to be
adopted in mining industry. This is partly due to
the fact that a typical mine has many working
faces and it is difficult to schedule the
shotcreting equipment efficiently.
However, as advancing the technology of
shotcreting and considering shotcrete is
generally stronger than mesh in regards to
prevent small pieces of rock from unraveling
from the surface of a excavation and it is
corrosion resistant, shotcrete is recently
considered to be a more effective support
system useful in excavations such as ramps and
haulages where long-term stability is important.
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33. Support recommendation of Pongkor underground gold mine
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34. Rock bolt properties
Shotcrete properties
H-beam properties
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35. In this study, two types of support system which applied by Pongkor underground
gold mine are analyzed by numerical modeling. The rock quality of Pongkor could
be categorized as class IV in regards to RMR. Ground support required for rock
mass class IV is rock bolt spacing 1m, 1.8m in length with mesh, and H-beam
(spacing<1 m) or rock bolt space 1m, 1.8m in length with mesh, and shotcrete
(10cm). Regarding the H-beam system, Pongkor underground gold mine has been
applying rock bolt, space 1m, 1.8m in length with mesh, and H-beam (spacing
0.6m) for sidewall and roof, and shotcrete with thickness 20cm at the floor to
prevent floor from heaving. Regarding shotcrete system, Pongkor underground
gold mine has been applying rock bolt spacing 1m, 1.8m in length with mesh, and
shotcrete (10cm thickness), and at the floor 20cm thickness of shotcrete is
installed.
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36. Support design of Pongkor
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37. References:
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o https://civilblog.org
o Deshmukh D. J. (2014), Elements Of Mining Technology, vol.-02, Denett Publications
o https://minewiki.engineering.queensu.ca/mediawiki/index.php/Cut_and_fill
o http://www.miningfunda.com/2016/10/cut-and-fill-stoping.html
o https://www.911metallurgist.com/stoping-mining-methods/
o https://www.britannica.com/technology/cut-and-fill-mining

38. T H A N K S
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