Underground Coal Mining Study

Onur Tuncay / 5706671 / UOW – Mine920 Underground Mining
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ASSIGNMENT A: UNDERGROUND COAL MINING
All drawings must be presented in a clear and professional manner. Relevant
reference must be provided.
1) For a coal seam of 2~5 m thickness, 5-100
dip and an overburden of 350-
500m with competent floor and roof and moderate geological structures, select
and describe the main means of accessing this coal seam, identify and discuss
factors need to be considered in selecting the appropriate means of access, use
neat diagrams for your description and discussion. (1500 words, 25 marks)
2) With the aid of neat diagrams, describe gateroads development process, the
main equipment used and their main functions; Discuss briefly roadway support
system and hazards control associated with roadway development (1000 words,
25 marks)
3) With the aid of neat diagrams, describe and compare different longwall
mining system (advance and retreat), identify and discuss briefly the main
hazards and problems associated with longwall mining and their solutions. (800
words, 25 marks)
4) With the aid of neat diagrams, describe different thick seam mining methods.
(1000 words, 25 marks)
REFERENCES ARE NOT IN PROPER SHAPE
THAT HAS TO BE.

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1. Mine access operations
1.1. Mining access types
Operations based on underground coal mining used all conventional means of seam access, such as:
- Adit,
- Shaft, mostly vertical shaft,
- Cross measure drift, decline or inclined shaft.
In New South Wales (NSW), the required limits of installing shaft needs to be considered at least two
roadways to apply separation for men and materials haulage, and ventilation if coal is transported
from underground to the surface by conveyor.
Some methods have been used for inclined mine access in New South Wales such as:
- Two shafts: Upcast designed for bulk coal winding, downcast transportation for men and
materials,
- Two shafts: Upcast for bulk coal haulage, downcast for ventilation only. One drift for men
and materials transport.
- Two shafts: Upcast for ventilation, downcast for men and materials. One drift for
transportation of coal by conveyor.
- Two shafts: Both of upcast and downcast for ventilation. Conveyor drift for coal
transportation, other one material and men transport with intake of clean air.
The capital costs for shaft sinking have increased in recent years. Therefore, one of the effective ways
of accessing underground deposit is cross measure drift. A nearly horizontal passages, adits, they
ensure fast transportation to coal seam by diesel based vehicles or conveyor belts carrying mining
equipment, The criteria for selecting the most suitable method of transporting and accessing an
underground mine depends on many variables. The variables involve:
- Coal clearance,
- Ventilation,
- Surface topography,
- Height of overburden,
- Environmental effects,
- Geotechnical and geological features,
- Personnel and equipment access,
- Mine closure,
- Capital operating costs,
(eds Kininmonth & Baafi 2009, p. 176).

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1.2. Portal construction
There are two basic alternative designs for portal construction for using as a cross measure drift:
- Excavation of open approach cut is applied until reaching to construct collars which probably
place in far away from competent ground after that reinforced concrete arch is
implemented to continue drift.
- This approach for excavation can be kept constructing same way until reaching competent
ground then next procedure is followed such: covering open cut section, installing metal
culvert liners and backfilling.
1.3. Driving of adits
Drift features
As the maximum angle of inclination on which materials can be conveyed on standards conveyors is
about 160
, belt drifts are driven at the angle to ensure minimum length. This angle is within the limit
where winding engine drivers are not required and is such that breaking devices on rolling stock can
bring them to a standstill in the event of a runaway. Thus 160
angle of inclination is virtually
universally adopted for major access of openings (eds Kininmonth & Baafi 2009, p. 187).
In this sample mine, as required minimum inclination, cross measure drift or inclined shaft with 100
can be selected, accordingly, the slope of the two main headings can be operated with 400/sin100
=
2304 meter as it can be calculated from the basic geometry formula (overburden is 400 m). In the
light of fundamental laws of mining, access of mine should be operated with minimum two shafts
(inclined) lying from the surface to underground, parallel to each other.
Used equipment’s in drifting
Eventually, a fairly wide range of sinking plant has been used for the driving of cross measure drifts,
depending on the method adopted. Among the combinations which have been used are:
- Drilling and blasting, slusher winch – skip system
- Road header machine for mucking and rock breaking – skip system
As a most suitable method for drifting, drilling and blasting techniques or road header machines are
the most worth to use, nevertheless drill and blast is conversely the most wide used technique for
drifting. After blasting, broken rock is continuously loaded and transported from excavated area to
the surface in a rail skip with pulling by wind system. Another approach to haulage, pickling made by
blasting operations can be transported by trucks carrying the waste from the face by the help of
loaders (eds Kininmonth & Baafi 2009, p. 189).
In the Table 1, by means of recent experiences in mite sites, for under 15 MPa vertical stresses, many
combination of development effected by roadway dimensions can be seen as a unit per week.

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Varying mining heights and longwall block lengths, typically for super unit mines – at least two
continuous miners, are shown in the table for 300 m coal face wide.
Table 1: Effects of Roadway dimensions to the development rates
Note: Date from Australian Roadway Development-Current Practices Final Report (2005)
http://www.undergroundcoal.com.au/roadway/workshops/C15005FinalReport.pdf
Supporting
Ground stresses are commonly doubled by mining operations, in a result of exceeding present
support or reinforcement elements. Particularly overburden with 400 m is quite equal to 1000 t/m2
(10MPa) vertical stress. The vertical stress formula is seen below:
Vertical Stress (MPa) = height of overburden (m) x 0.025
Additionally, Roadway excavated less than angle of 200
shows that it is one of the best variance of
roof conditions, faster development rates and greatest stability features. Otherwise, in the slopes
more than angle of 200
will be highly monitored the major horizontal stress which may lead roof
failure.
Wide usage of reinforcement for roof is rock bolts for primary installations in inclined shafts. Then
cable bolts is installed to extend above present bolts and increase roof stability conditions. Another
method to increase the rock strength and prevent counter fracturing of rock, is injection of chemical
bonding agents such as Polyurethene into the rock (eds Kininmonth & Baafi 2009, p. 279).

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2. Underground operations
2.1. Bord and pillar
The basic understanding of bord and pillar method involves application of dividing the coal seam
into regular or particular blocks with array by excavating main headings, which are intersected at
regular intervals by bonding cut-throughs. The blocks of coal are fully surrounded, or nearly, by
roads are called as “pillars”. The pillars ensure a support to overcome extreme load of
overburden during “first workings”, also called as development process. Actually, in Australia, for
long years, room and pillar method has been the main underground mining method for the
medium-thick seams (eds Kininmonth & Baafi 2009, p. 297).
Figure shows a seven-heading bord and pillar underground development and equipment related
to operation.
Figure 1: Plan view of room and pillar section with the assistant equipment
Illustration received from http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2225-62532012001000003

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Barrier pillars
Barier pillars are longer natural solid structures rather than their width, and applied for separation of
panels or isolation of sealed areas. They must handle required multifunctional tasks:
- To overcome giant abutment loads placing around working areas as result of driving panels,
- To obtain optimisation of panel dimensions; especially width, which prevent unwanted
occasions by naturally supporting roof conditions in roadways and particular zones.
- By means of sufficient width and stability of panels, isolate working areas against gas
leakage or inrush (eds Kininmonth & Baafi 2009, p. 257).
Chain pillars
In Underground coal mining, particularly in longwall operations, chain pillars play an important role,
such barrier pillars, to reduce roof stress, or encounter the many stress components imposed to the
working place, even if the goaf produced, they can ensure subsidence control. Primary task of
driving chain pillars is to reduce abutment stresses possibly affecting the load over the barrier pillars,
cut throughs and main headings. Other types of pillars such as production or yield pillars are rarely
used just in case (eds Kininmonth & Baafi 2009, p. 257).
2.2. Development work
First workings, also called as development work, is driving for creating infrastructural ways to employ
operation equipment - such as shuttle cars, trailing cables, bolters, conveyor or continuous miners- in
main headings and cut-throughs by dividing the untouched coal seam to be operated into the certain
pillars at interval. Development works are operated the following purposes:
- To maintain multiple roads supported by pillar in a long term for accessing coal deposit,
- To obtain appropriate conditions for excavating pillars in the end of operations,
As required logical aspects, it is clear to mention that longer pillars provide less development process
and less number of panels to be excavated. During development, the process at the face includes
different three tasks. To reduce downtime of equipment placed in a cycle such delays in installing
roof supports, among shuttle cars or other infrastructural services as much as possible. (eds
Kininmonth & Baafi 2009, p. 312).

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Figure 2: Sample positions for electrical cables and face equipment in room & pillar
(eds Kininmonth & Baafi 2009, p. 300)
2.3. Used equipment in development process
The list of increasing usage of equipment in development stage can be seen as follow:
- Continuous Miners
- Shuttle Cars
- Feeder-Breaker Units
- Conveyer Belts
- Bolters
Continuous miners
Continuous miners are considered as suitable for first workings due to allowing single passing, and
they also widely use extendable belt conveyors to haul extracted coal after removed the seam.
Remote controlled ones are initiated to work in various challenging coal seams and some of them
became quite popular which ones can be driven by computers. Within in 1 m of the face, many of
them are capable of installing support with their roofbolting mechanism with ring and two rib

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bolters. However the main required task of CM should be to mine coal from the face and load it to
the conveyor at no interval because in some weak seams, early enforcement for roof should be
applied rapidly. Therefore, innovative continuous miners instead of conventional ones are not only
quite suitable to bolt and enforce the roof at the same time but they also are very productive
without downtime (Coal Education, n.d.)
Developed characteristics of the most innovative continuous miners involve the following:
- Allowing remote control by displaying in monitor visually
- Wider throat of chain conveyor allows shuttle cars to haul coal quickly
- Data logging of used machines can be applied on board
- Roof and rib bolters on board (eds Kininmonth & Baafi 2009, p. 300).
Figure 3: JOY 12ED30 Series, Single Pass Miners/Bolters with capable of excavating, drilling and
bolting in same machine
Data received from Komatsu official website, https://mining.komatsu/underground-mining/room-pillar-entry-
development#!entry-drivers
Figure 4: Conventional continuous miners, series of JOY 14CM15 and JOY 14CM10 respectively
Data received from http://www.coaleducation.org/technology/Underground/images/Joy_Mining/14CM15.jpg -
http://www.coaleducation.org/technology/Underground/images/Joy_Mining/14CM10.jpg

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Shuttle cars
The most used shuttle cars in Australia can be seen in Figure 5.
Figure 5: JOY shuttle cars
Data received from https://mining.komatsu/product-details/shuttle-cars
The shuttle cars allow loading the coal mined by continuous miners in the development face and
transporting from the face to feeder breaker unit. Their main power engines are based on
electricity generated by alternative currency with a trailing cable. With 4 – 20 ton capacity of
payload, they have various types of shuttle cars which each one can be used in different working
conditions due to varying height and width of the roadways. Operation boundaries unfortunately
depend on length of trailing cable which is, allowing around 150 m.
Feeder-breaker units
As can be understood from its name, these beneficial machines allow the loaded coal on it both of
breaking and feeding. Broken coal already mixed with water in the unit is fed to conveyor belt
directly. If coal is not fed on the conveyor belt properly, many obstacles for operation occur
because of frequently faced the case of high ratio of blocky lumps causing damages in conveyor
system, tracking problems, and conveyor belt spillage. By means of feeder breaker unit, mined
coal can be transported with uniform and oversized pieces. It can be seen in Figure 6.
Figure 6: Feeder-Breaker Unit
Data received from Komatsu official website: https://mining.komatsu/product-details/ufb-33

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Extendable Conveyors
This type of conveyors are lying throughout from end of the panel operations underground to
passing entire roadways, then to the surface. Its sample position was shown in Figure 2.
Additionally, extendable conveyors certainly maintain continuous activity by hauling the coal from
continuous miners to the feeder breaker unit rather than shuttle cars do. They are considered the
most common alternative haulage system, which are being now applied in many underground coal
mines by using chain haulage systems and flexible conveyor train, which is seen in Figure 7.
Figure 7: Chain haulage systems and flexible conveyor train respectively
Data received from Komatsu official website: https://mining.komatsu/docs/default-source/product-
documents/underground/room-and-pillar-entry-development/rsa-hs01-1114-v1.pdf?sfvrsn=38
Bolters
Roof bolters are necessarily used in underground coal mines to stabilise roof conditions and
ensure more secure working conditions for workers, by drilling bore holes and installing rock bolts.
These machines are able to drill with four-hand bolters -also two-hand or single hand bolters exist-
operation length varying from 1.8 m to 6 m as can be seen in Figure 8.
Figure 8: Several views of a sample Quadbolter.
Data from: https://mining.komatsu/docs/default-source/product-documents/underground/room-and-pillar-entry-
development/bolting-products-brochure---rb04-0712.pdf?sfvrsn=34

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Figure 9: Loader
Data received from https://mining.komatsu/docs/default-source/product-documents/underground/room-and-pillar-
entry-development/en-14bu27l01_loader-brochure.pdf?sfvrsn=42
2.4. Roadway support systems
Rib support with fibreglass dowels and steel roof bolting techniques are commonly applied in main
headings. The rock bolts are generally installed through steel mesh or light steel straps combined
with shotcrete. The most common usage of bolt length is 1.8 m, of course, its lengths depends on
many parameters, particularly roof strata, otherwise longer or shorter at length bolts are also in
use. In Australia, main headings are driven with maximum 5.5 m wide and around 3.5 m height,
and pillar dimensions 50 x 50 m, which these are considered a suitable working environment to dip
up to 600 m. Figures 10, 11 and 12 show typical roof support techniques in many mines to give a
sample design (eds Kininmonth & Baafi 2009, p.307).

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Figure 10: Using straps, props and bolts
(eds Kininmonth & Baafi 2009, p. 308)
Figure 11: Using props, bolts, rail bars and straps
Received from (eds Kininmonth & Baafi 2009, p. 309)

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Figure 12 Using timber only as a roof support method
Addition to design of supports, Figure 13 illustrates the relation between support length and
installation times, which have pointed out how time management can be applied efficiently if
general downtime of equipment and operations wanted to reduce (Coal Education, n.d.).

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Figure 13: Illustration of relation between installation time and roof bolt or tendon length
Received from http://www.undergroundcoal.com.au/roadway/supp_length.aspx
2.5. Hazard control in roadway developments
In New South Wales, Work Health and Safety (Mines and Petroleum sites) Consolidated
Regulations 2014, the following reasons indicate that any of them occurs throughout mining
operations should be called principal hazard, and these accidents probably lead single or multiple
fatalities.
- Subsidence
- Inrush
- Explosion or fire
- Operation places and roads
- Strata or ground failure
- Outbursts
- Winding systems
- Spontaneous combustion
- Airborne contaminants
(Regulation 5, Meaning of principal hazard)
Stable roof/ribs and subsidence
In a long term or during the life of a mine, proper support of roadways is very important,
particularly steel support, arches, roof bolted steel enforcement or roof bar and legs. Additionally,
chemical anchoring is widely used.

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Roadways which will be required for a major part of the life of a mine are, in many cases,
supported on some form of steel support, be it roof bar and legs, roof bolted steel members or
arches. Roof bolts utilising split and wedge, and chemical anchoring are employed.
Techniques used to provide protection from slabbing ribs include:
- Simple lagging,
- Steel roof bolts with plates or pads,
- Fibreglass dowels with or without plates,
- Steel wire mesh covered by bolts, dowels or sprags,
- Steel straps covered by bolts or dowels,
- Fibreglass mesh covered by bolts or dowels.
In final report of ACARP, many mines in this research applied a variation of 2 rib bolting rigs and 4
roof bolting rigs. Roof bolts also are installed varying from 1.8m to 2.4m in length, each in 1.5
meter four 1.8m bolts to eight 2.4m bolts in every meter, last but not least, 2.1m bolts in every
meter (41% of the reported mines).
32% of the mines stated that 4m or 6m tendons are applied for primary workings, routine basis or
required implementation of 13 different supports result of strata management and trigger levels.
Other implementations in roof support as following:
- Length of rib bolts vary between 1,2m – 1.8 m.
- Interval of intensity is one-1.2m bolt/rib/m and one to three 1.2 m, two 1.5m, or two 1.8
bolt/rib/m
Final report also states that companies participating research were implementing three bolts with
full rib meshing for each cycle per rib. (Underground Coal Website, n.d.)
Inrush
In the light of previous experience of miners and reported incidents, Table 2 shows some of these
cases as a distribution of accident sources. Primary causes of accidents can be stated that:
- Insufficient barriers
- Inefficient mine planning
- Inefficient protective boreholes
-
Table 2: Common sources of water incidents
Source of Water Number of Incidents
Contact with surface water 9
Contact with surface unconsolidated deposits 8

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Strata water entering workings 2
Shaft Sinking 4
Clearing old shafts 14
Contact with abandoned old workings 162
Failure of an underground dam 9
(eds Kininmonth & Baafi 2009, p.793)
In a nutshell, surveying and investigating of rock strata of the mine site should be carefully
controlled and checked counter possible water inflow. The underground water that leaks to the
mine must be stored to use it in order to reduce dust rate over the air. (eds Kininmonth & Baafi
2009, p.781)
Outburst
In coal mining, it has been described as an instant gas burst of coal, expect rock burst. Where the gas
mixed with carbon dioxide and methane causing many accidents has several primary reasons:
- Depth of mining
- Mining operations
- Faults and folds
- Seam thickness
- Gas content and its environment
- Strength of the coal seam
- Rank of coal seam
- Permeability
- Volumetric change
- Cleats and joints
Outburst management needs analytical and frequently controlled approaches, to predict and
prevent possible incidents before happen. There are wide applications for prediction of,
prevention against, and control of outburst in mine sites:
Prediction methods:
- Seams having complex geological structures are more prone to outbursts if high gas
conditions are prevalent.
- Gas monitoring systems such as Tube Bundel System or Telemetry System.
- Seismic reflection surveying
- Logging in seams boreholes
- Detection of igneous intrusions
- Detection of zones poorly drained of gas
- Radio imaging method (RIM)
- Monitoring for outburst precursors
- Estimating Gas Threshold Values (GTV)

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- Estimation methods of gas content such as direct, analytical, volumetric, gravimetric or
probabilistic methods.
Gas drainage is a highly adoptable action to obtain a minimum gas inflow to working area.
Surface drainage mostly includes drilling boreholes on a grid pattern form the surface to the
coal seam. The spacing between the holes varies 250-500 mm as the diameter of surface
holes is 150 to 300 mm. Underground drainage can be implemented in development headings
(Local drainage), along the panels (Inseams gas drainage) and below or above the working
seam (Cross measure drilling). Holes vary from 250 to 400 m in length but can be increased
over than 1500 m if required. Figure 14 shows a common method of drilling holes ahead of
the roadway. Figure 15 shows typical drilling technique used in panels.
Figure 14: Drainage in a development heading
Figure from http://undergroundcoal.com.au/outburst/gas_drainage.aspx

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Figure 15: Gas Drainage in longwall system
Figure from http://undergroundcoal.com.au/outburst/gas_drainage.aspx
Roads or other vehicle operating areas
Poor road conditions are threatening miners’ health and safety because of slowing down mine
vehicles; poor horizon and vision control – especially in cross-sections - lack of smart caution
systems, a trigger to crushing of vehicles in cross-sections; leaving coal in floor.
Ventilation
Usage of multiple fans at different shafts plays an important role for increasing ventilation capacity
progressively and intensively. The regulations made by Australian Government states that
maximum methane proportion in the air should be 2%.
In a coal mine, any vehicles of generated by internal combustion engine should be abandon in
return airway by mine operator if the general concentration of the air greater than 1% (as a
volume) but less than 1.25%, If methane ratio in the air is greater than 1.25%, these types of
vehicles should be shut down immediately (Work Health and Safety Regulations, 2014, pp. 53).
Electrical safety
All used cables in Australia are mandatory to accord standards determined by Australian Standards
Association (ASA). These standardised cables should be extra cautions counter traffic damage,
anchored and properly reeled. Also methane monitors are able to automatically shut down
electricity in the possible incident area when gas level increases.

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3. Longwall mining
After the development panels have been driven, longwall mechanism is installed and excavation
initiates (Figure 16.a). In the face to be mined, overlying strata is ready to be caved behind chocks
(support units with hydraulic legs as shearer and with support equipment - the face – advances
(Figure 16.b). Maximum coal seam height with 4.57 m can be chosen for method of advancing and
retreating (ed. Hustrulid 1982, p.791)
Figure 16: Illustration advance and retreat longwall operation (a-b)
Retrieved from http://longwall.miningst.com/longwall-advance-mining/
Mines commonly use bi-directional (Bi-Di) cutting or unit-directional (Uni-Di) cutting with a
backward, forward or reverse snake, depending on geological, environmental or management
conditions, last but not least, longwall top coal caving. The majority of longwall operations in
Australia use a uni-directional cutting technique that provides simple operation, environmental
benefits, minimal manning and improved horizon control (eds Kininmonth & Baafi 2009, p.352).
3.1. Bi-directional cutting system
It is also called as the full web mining of the seam in the single pass of shearer. In every beginning
of the face operation, shearer mines the coal from here to the end. As the shearer mined through
the face, the chocks and their legs are advanced at the same time when AFC follows chocks.
The shearer should be shuffled for next excavation after every single passes, by getting back into
the entrance of main/tail gate to maintain full face excavation in each direction. The shuffle
maintenance may take time because of wearing on some equipment unless the snake is not
inflexible. Less than 180 m longwalls, described as short faces, Bi-di excavation method is not
sufficient application.
Several factors which may restrict the usage of Bi-di extraction method are;
- Reliability of chocks (age, maintenance, etc.)

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- Possible requirement of two shearer operators
- Horizon control troubles
- Problems between AFL/BSL and outbye system (may cause cutting speed rate)
- Poor flexibility of cutting cycle
- Mandatory to employ experienced operators
Advantages of Bi-Di excavation may be:
- In poor conditions, better face support
- Less requirement for support systems
- Minimum creep due to snaking in both direction
- Maximum efficiency in thinner seams
3.2. Uni-directional cutting systems
This method (Uni-Di) applies the excavation of the web in two directions, round-way between
tailgate and maingate. Other words, the shearer passes across the coal face to mine two times.
While the first excavation is passing, the chocks are advanced then second excavation, return
cutting, is passing the Armoured Face Conveyor is advanced. Figure 17 shows Uni-Di cutting
system.
Figure 17: Bi-Di Cutting System
(eds Kininmonth & Baafi 2009, p.354).

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Uni-Di method contributes reducing downtime to be spent for change of shuffle every end of the
face. By this way, Shearer must travel faster to catch up Bi-Di sequence method because this
technique requires passing the face two times every cut.
There are several important factors should be taken attention such:
- When the shearer’s velocity inclined, the demand on the support system may increase
- Requirement for transport at faster speed
- Snaking in one way each shear may lead a creep
- When automation is poor, extra manpower may be required
Some advantages may be:
- If mechanism is simple, learning the system may be easy
- Only one drum must be controlled during the cycle
- Support advance is on the side of the operator so it is more secure
- Loading on the conveyor has simpler arrangements
- Support control and cutting cycle is very suitable on various conditions
- Horizon control is not problem when the AFC came back to re-grade floor.
Backward Snake
Traditional Uni-Di sequence includes a backward snake at the tailgate, allowing the shearer to
excavate across the roof through the tailgate. Accordingly, when cutting through the tailgate, roof
supports or chocks should be advanced on the side of the operator (shearer). In some cases, dust
may be quite problem causing air contamination due to support advance in this system. The figure
shows Uni-Di cutting backward snaking.

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Figure 18: Uni-Di cutting system (backward snake)
Forward snake
To overcome the dust problem, the system of forward or advance snake at the tailgate can be
applied. In this case, required advance support units will not be necessary intake side while snaking
at the tailgate, however it may be mandatory to apply AFC in reverse side while snaking into the
maingate, or double snake can be applied on the face. While typical Uni-Di cutting sequence, present
snaking can be switched to reverse in order to decrease creeps through the gateroad. Figure 19
shows Uni-Di cutting forward snaking.

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Figure 19: Uni-Di cutting system (forward snake)
In a nutshell, the system of Uni-Di cutting model is more practical and less maintenance
requirements for equipment. Therefore it is commonly used.
Half Web
Half web model contributes decreasing the load overlying the equipment and burdening on the
face to fracture the coal. This method is combination of Bi-Di and Uni-di models. Because of
excavating single coal web, it may be also described as a Uni-Di model. The result of this method is
clearly production friendly, and allows faster shearer cutting rates due to fewer loads into the face
for each pass (eds Kininmonth & Baafi 2009, p.356).

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Figure 19: Uni-Di cutting system (forward snake)

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Also Figure 20 shows comparison among four methods each other.
Figure 20: Summary of system advantages and disadvantages

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4. Different Thick Seam Mining Methods
Since that longwall machine can successfully applicable to many cases nowadays, it is one of the
most common method for secondary excavation methods for thick seams. Anyhow there are still
some mines that longwall is not convenient to use.
4.1. Open ended lifting
Series of drives are generated down the goaf sides of the column in the picture. Rows of breaking-off
propos hold the roof column for the drives along the goaf side. Figure 20 and 21 shows open ended
lifting method.
Figure 20: Open ended lifting – A
Advantageous places to use this method are;
- If the strata are durable and feels like a goaf collapse that also men and machines can be
detached to security.
- When the roof stata stands durable against breaking-off propos and drops repeatedly In
order to lift finalization to departure of the timber.
Disadvantageous usage of this method;
- Machine crew was not safe except the wooden props which are set along the goaf edge.
- Goaf falls streak to goaf operators for a long time.
- Unhealthy positions occur in order to stress changes in the stata when it is holed at the back
of the pillar.
- Since the miners waste too much time to replace the strong roof lifts in and out, it also get
operators upset as well.
- Because of the chain moves too much production time was consumed.

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- When the goaf is siphoned out, It inhibits the miner to get out or get back in.
Figure 21: Open ended lifting – B
Furthermore, this problem cause chain of extraction and also results in subsequent coal loss
(Mining Science and Technology Website, UOW).
4.2. Split and lift
The main aim of the method was limitation of the problems relevant to the open ended lifting. The
method cut down the length of each lift, which provides the miner and its crew to streak less
cantilevered roof. To revise the ad hoc for the extraction chain is unsusceptible and it demands
tramming time reduce in between successive lifts.
The maximum thickness of a cover of the goaf edge is 2 m, which leads a fact that lifts are not open
ended. Commonly in coals the covers are at the width of 2 – 3 m which is not sufficient to inhibit
mistakes and also can cause safety problems. In case the fenders are developed to an acceptable
thickness, there would be need to the total extraction by “pocketing” system which is displayed on
the picture (ed. Hustrulid 1982, p.792).
Figure 22 illustrates split and lift method.

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Figure 22: Split and lift method
http://pillar.miningst.com/modified-split-and-lift/

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BIBLIOGRAPHY
- Hustrulid, WA (ed.) 1982, Underground Mining Methods Handbook, The American Institute
of Mining Metallurgic and Petroleum Engineers, Maryland, USA.
- Kininmonth, RJ & Baafi, EY (eds) 2009, Australasian Coal Mining Practice, Australasian
Institute of Mining and Metallurgy, Victoria, Australia.
- Kentucky Coal Education, viewed 1 September 2017,
<http://www.undergroundcoal.com.au/roadway/supp_length.aspx>
<http://www.coaleducation.org/technology/Underground/continuous_miners.htm>
- New South Wales Government, Work Health and Safety Regulations 2014, Part 2 –
Managing Risks, pp. 53, viewed on 30 August 2017,
<https://www.legislation.nsw.gov.au/regulations/2014-799.pdf>
- New South Wales Consolidated Regulations, Work Health and Safety (Mines and Petroleum
sites) Regulations 2014, Regulation 5 – Meaning of principal hazard, viewed on 24 August
2017,<http://www.austlii.edu.au/cgi-
bin/viewdoc/au/legis/nsw/consol_reg/whasapsr2014563/s5.html>
- University of Wollongong - Underground Coal Education Website– ACARP, Outburst and gas
drainage, viewed on 19 August 2017,
<http://undergroundcoal.com.au/outburst/gas_drainage.aspx>
- University of Wollongong - Mining Science and Technology Website, viewed on 25 August
2017,
<http://miningst.com/index.html>
<http://longwall.miningst.com/>
<http://rockbolting.miningst.com/>
<http://pillar.miningst.com/>
<http://pillar.miningst.com/open-ended-lifting/>

30
ATTACHMENTS
JOY SHUTTLE CARS
https://mining.komatsu/docs/default-source/product-documents/underground/room-and-pillar-entry-
development/rsa-hs01-1114-v1.pdf?sfvrsn=38
JOY BATTERY HAULAGE

31
JOY CHAIN HAULAGE SYSTEMS
JOY 12CM CONTINUOUS MINERS
development/12cm-brochure.pdf?sfvrsn=36

32
FEEDER BREAKERS
https://mining.komatsu/docs/default-source/product-documents/underground/room-and-pillar-entry-development/en-
fb01_feeder-breaker_brochure.pdf?sfvrsn=50

33
JOY 14CM CONTINUOUS MINERS
https://mining.komatsu/docs/default-source/product-documents/underground/room-and-pillar-entry-development/14cm-
brochure.pdf?sfvrsn=34

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