2. Mining Methods
• Coal is mined by two main methods -
Surface or ‘opencast’ mining and
underground mining.
• The choice of method is largely determined
by the depth,thickness and no. of coal
seams, geology of the coal deposit and
other factors.
4. Ideal conditions for Opencast Mining
1. Thickness of coal seams - > 5m
1. Flat gradient - < 1 in 6
1. Strike length - > 1 km
1. No.of seams - Less the better, with
higher thickness
5. Coal without stone bands
6. Free from surface structures / features.
7. Preferably non-forest land.
8. Availability of adequate place for dumping.
9. Stripping ratio depending on quality of the coal
5. General planning studies
No fixed procedure – country-wise differences
1. Conceptual study, data reliable upto -- 75%
Review
2. Pre-feasibility study - data reliable upto - 80%
Additional data, modify
prepare, management acceptance
3. Feasibility Report/DPR - data reliable upto - 85-90%
4. Detailed designing LTP/MTP - data reliability - 95%
5. Operational planning (STP) - -
6. Basis for the initial study is Geological Report
• There will be some overlap between various studies/reports.
• Every step deals with Mining Technology, equipment, production
scheduling, capital cost, revenue cost, internal rate of return, dispatches etc.
However the degree of accuracy of data on the above aspects increases with
each step.
• Generally After F.R. approval, there is need to go in for long term planning,
medium term planning (about 5 years) and S.T.P. Short-term planning (6
months – one year).
•These reports should adapt circular analysis approach by considering
various aspects like additional information available while operating the mine,
slippages occurred, reserves, pit-slopes, pit-limits, pit scheduling to control
faster rate of extraction from coal inventory which otherwise may lead to
reduction in coal production in subsequent years or more equipment for
higher OB removal to maintain targeted production.
7. CONCEPTUAL MINE PLANNING / PRE-FEASIBILITY
Deposit Tech-Aspects Economic aspects
Resources Production requirements
GR/MR Mining
Technology Minelife requirements
Mining depth Logistics,
Strata Sequa Options and
Suggestions Roads etc.
Thickness of
- coal Cash out flow
- waste Equipment
Cash inflow
- inter burden Required rate of
Coal Quality Surface
Constraints Return
Slope stability Cut-off SR
Water
Conceptual Mine Plan
(Open pit layout, equipment)
Modification of concept
and or optimization
Pre-Feasibility Study
Accepted – Management Not accepted –
DPR New attempt
8. Steps in design of Opencast
A. Study of deposit exploration (GR)
B. Final pit limits.
C. Development sequence.
D. Design of Access Ramp and Haul Roads
E. Pit design
F. Annual production capacity – system availability – Mining
technology
G. Main Mining Equipment – Matching to Mining Plan
H. Optimizing Dumping strategy and balancing
I. Year-wise / stage – wise plans
J. Financial viability (Capital & Revenue)
K. Coal Washing
L. Environment stipulations
9. A. Study of GR on the deposit Exploration
Salient Information
• Extent of deposit i.e. strike and dip rise widths.
• Geology – Geological succession, sequence of beds, drilling, logging, no. of
seams, sequence of coal seams, description.
• Inter seam partings.
• Structure – No. of faults, Throws, dip of seams and beds
• Reserves – Quality wise/seam wise/depth-wise etc. based on Block model,
Gridded seam model & polygonal Model
• O.B. volumes & S.R. – Sector-wise, depth-wise etc.
• Coal seam analysis, proximate and ultimate , Ash etc. & OB strata hardness etc.
• Drilling details (Lithology)
• Physiography
• Climate and Vegetation
• Preliminary EMP information
10. A. Contd.
PLATES
• Location Map, Top Sheet map, Roads, Lands (Forests), Rivers etc.
• Topography – Hills, contours, rivers of Flats
• Geological Map – in crops, Faults
• Graphic Lithologs
• Graphic correlation charts
• Floor/Roof contour plans of all seams
• Seam folio plans of all seams (seam out cop, floor contours, faults,
isograde, isochore, iso depth).
• Geological cross sections
• Seam structure of all seams
• ISO parting plans
• ISO excavation plan for lower seam (surface constraints, boundaries,
faults at seam level, excavation area)
11. A. Contd.,
Additional Data required -
-Geo-technical data – diggability of materials, slope geometry and stability of
Working/permanent slopes, spoil pile configuration
for outside/inside dump, stability, grainsizes after
blasting etc.
-Ground Water – Dewatering and depressurization
hydrology - Impact of dewatering on surrounding areas
- Impact on water quality
-Surface hydrology - Water quality
- make off water
- Mine flood protection
- Options for discharge of dirty water and various
discharge systems.
12. B. Final pit limits
The criteria for delineation of boundaries of an Opencast Project are:
Rise side boundary - Usually incrop of the bottom most seam
Lateral sides - Usually by Geological disturbances like faults,
surface structures / features like nalah,
river etc or limitation of the strike length of the deposits.
Dip side - Depends on the economical stripping ratio,in
absence of natural constraints
13. B Contd.
B. Final pit limits
Final Pit limits
Haul analysis
Lead,lift increase cost – decides mode of transport
Dump area 100m from mine boundary
Dump limits available are Dump area 50 m from internal access road.
Dump area 80-100 m. from mine
infrastructure
OB volumes - Final slopes
Mineable Reserves – various losses, batter, barrier etc.
- dilution etc (0-1 m against Roof,floor)
Maximum depth increases haul cost (30-40% of total cost at 1 1/2 Km lead.
Boundaries are drawn as above & Coal, OB ,SR are estimated
14. B. Final pit limits B Contd.
Estimation of Coal, OB & Stripping ratio
Rough assessment is given below
• Assuming Pit slopes of 450, the Quarry floor and Quarry surface are
delineated
• Volume of Coal & OB = Average area x Average depth - (A)
• Average area = (Quarry surface area + Quarry floor area) / 2
• Average depth = (Minimum depth + maximum depth) / 2
• Volume of Coal=(Quarry floor area x Cumulative thickness of all coal
seams) - (B)
• Coal in tonnes = Volume of coal x Specific gravity – (C)
• OB Volume = Coal + OB Volume (A) – Coal Volume (B) - (D)
• Stripping ratio = OB Volume (D) / Coal in tones (C)
For accurate S.R,the volumes of OB and coal are to be made seam wise
15. B Contd.
B. Final pit limits
The boundaries are firmed up based on the economic stripping ratio.
Economic stripping ratio varies with:
• Average sales realization i.e. higher the quality of coal,
higher the realization.
• Capital investment requirements
• Operating cost.
• Also surface constraints
The following thumb rules may be of some Help (with outsourcing OB removal):
Projects are likely to be economically viable upto a maximum SR indicated
against the grade of coal
Grade Stripping ratio
(Cum/T)
F 6
E 7
D 8
C 10
16. C. Development Sequence
-Opening the deposit – Access trench
-Box cut – To accommodate all equipment
-Mine phases – Depends on the shape of the property
-Progress of Benches
-Coal production schedules
-OB excavation schedules
Note:- Maximize inventory of coal in the initial years
-Differ OB stripping requirements as much as possible – Average
SR versus natural SR
-Income generated in the first 5 to 10 years but not remote
economics will either make or break the project.
-Profits for in the future have practically no impact on the project NPV.
Each successive phase will be less profitable and the ultimate
limit will be loss even after ploughing in earlier profits.
17. D. Design of Access Ramp & Haul roads
Location of Access ramp is guided by the following:
1) Generally located at the minimum depth of incrop of bottom most
seam – So as to reduce initial waste stripping (unproductive work)
2) Should facilitate maximizing of internal dumping and sectional
working.
3) Should be near the External dump / Coal yard / Mine service
facilities etc.
4) Main haul road upto the pit limit should be planned in the
beginning only.
5) Since haul costs constitute about more than 40% and tyre costs
about 10% of the total mining costs,priority for design,construction
and maintenance should be given.
6) Gradient,width,drainage,curves,super elevation,base,sub
base,type and thickness of top dressing should be like that of
national high ways for heavy traffic.
18. D Contd.
D. Design of Access Ramp & Haul roads
Haul roads
Sl.No Particulars
1 Width Should facilities two way traffic, dozer
movement, formation of drains, lighting
arrangement (Normal width – 30m,but
depends on capacity of dumpers).
2 Gradient 1 in 16 Short ramps 1 in 10
3 Lesser number of
curves
4 In flat seams of haul roads can be formed over the floor of
larger strike length the seam
5 In steep seams Haul road for Coal & OB benches can be
planned along highwall slopes say every
30m. This will also facilitate internal dumping.
19. E. Pit design.
General design parameters and planning data
• Density of seams, total coal column thickness
•Thickness of partings
• Gradient
• Geological disturbances
• Strike lengths, shape of property
• Geological Reserves
• Surface constraints/adjacent habitat
• Dump yards availability with lead and lift
• Mining system, optimum mining concept
• Depth of operation, mineable reserves after various losses, OB volumes, SR
• Spoil characteristics
• Work practices in the Area
• Diggability characteristics
20. E Contd.
E. Pit design
As per Regulation 98 of CMR 1957,
In alluvial soil etc. - Sides shall be sloped at 450 or
Benched – height not more than 1.5m
Width – not less than height
In hard ground - Sides adequately benched/sloped so as
to prevent danger from fall of sides
Coal - Sides shall be sloped at 450 or
Benched – height not more than 3m
However, exemption can be sought from Inspectorate.
21. E Contd.
E. Pit design
Overall slope of a pit depends on several factors of the pit slope:
a) Geological disturbances like faults etc.
b) Hydrological condition of strata
c) Orientation of slip planes
d) Nature of strata – i.e. hardness, material consolidation etc.
e) Depth of workings
f) Design of haul roads & ramps in the highwall
g) Stratigraphy – thickness, spacing of the clay bands or other weak
layers
22. E. Pit design E Contd.
In general for OC mines upto a depth of 200m, overall slope angle of 450 is
permitted.
23. E Contd.
E. Pit design
For deeper mines flatter highwall slopes will be necessary from safety point of
view (for 35 T dumpers & above)
24. E. Pit design E Contd.
For deeper mines flatter highwall slopes will be necessary from safety point of
view (dumpers below 35T capacity)
26. E Contd.
E. Pit design
Working benches:
1) General
Width - 40 – 45m
Height - Generally equal to height of the boom or in some cases
upto 3m above the boom height.
In case of Backhoe – digging height of machine
Bench slope - 560 to 700
2) Dragline:
Width of the cut - 60m
Height of bench - maximum digging depth
3) In order to even out the yearly OB removal quantities and the
economics sometimes alternative workings and non-working benches
(around 25 m wide) are proposed.
27. F. Fixing annual production capacity
After defining the boundaries, the annual production capacity will be fixed
based on the following criteria :
1) The available mineable coal reserves
2) Geometry of the deposit - Strike & dip rise lengths
3) Structure of the deposit - Thickness of seams, partings, faults,
gradient etc.
4) Linkage - Basket, Captive use etc.
5) HEMM configuration - Capacity of HEMM.
6) Surface structures - Limits the material to be blasted.
28. F Contd.
Excavator machine productivity –
Based on ,
-Dipper cycle time
-Waiting time for truck spotting
-Bad blast factor
-Truck loading time etc.
Annual capacity is based on
-Equipment available hours
-Utilization percentage
Proper fragmentation,less throw off material,bench
height,bench slopes ,avoiding toes and secondary
blasting,improves shovel efficiency
Optimum fragmentation-cost of drilling,blasting vis-
à-vis cost of dozing,loading,hauling and dumping.
29. F Contd.
System availability as a function of individual components
Calendar hours-(365x24) (Figures are Indicative only) 8760
scheduled working
Holidays and bad weather 2.5%- hours(SSH) 8463 / 6140
Operational delays-blasting, relocations,shift
change,Lunch etc 1 Hour/Shift(8%)
Preventive maintenance-i.e annual,weekly,daily,shift 15% of SSH Scheduled operating time or
wise and unexpected break downs Availabilty- 100% Equipment available hours 6563/4390
Shovel,dumper system 97% Effective Operating Time 6366/3960
12% - Crusher + 1 Conveyor 85% Effective Operating Time 5559/3730
2% Drop for each Belt
73%
System Availability 4804/3160
30. G. Main mining equipment
For Various Technologies
1) Shovel Dumper technology.
2) Dragline technology
3) Inpit Crusher – conveyor – spreader – technology.
4) Continuous Mining technology – Bucket wheel excavators.
5) Rock Breaker technology.
6) Surface Miner technology.
31. G Contd.
Note: In seam Mining is always practiced in flat seams while in case of
steep seams Horizon mining, with its disadavntages, may have to be followed.
32. G Contd.
G. Main mining equipment
1)Shovel dumper technology:
• This is the most commonly used technology in Opencast mines.
• Basically two variants – Rope shovels and Hydraulic shovels.
• Shovel used for excavation & Dumper for transport of material.
• Bucket capacities vary from 0.9 Cum to 40 Cum with matching
Trucks/Dumpers of 16 Cum to more than 240 T.
• Can be deployed for removal of varying thickness of materials.
• Harder materials require blasting.
• Can be deployed for removal of steep & thin seams (hydraulic shovels).
33. G. Main mining equipment G Contd.
2)Draglines:
• A dragline bucket system consists of a large bucket which is suspended from a
boom with wire ropes.
• Draglines are deployed wherever there is scope for side casting overburden
above coal seam into the de-coaled area.
• It is very cost effective technology & can be deployed in flatter seams.
3)In pit crusher conveyor technology:
• The drilled & blasted OB is loaded by shovels and transported by dumpers to
Crushers. The crushed OB is then transported by a series of conveyors into a
spreader for dumping.
•Can be used in steep seams where laying of transport roads for the trucks is difficult.
•While S.R indicates volumes,cut off ratio indicates depth and reflects in dumper
haulage cost,which increase with depth and may become prohibitive where in
alternative haulage system may have to thought off.
•Ideally suited where material has to be transported over a large distance & lift.
4)Continuous Miner Technology:- Bucket Wheel Excavators
•Presently being used in Neyvali, Lignite Opencast mines, having soft strata.
•The buck wheel excavates the material without blasting which is transported by a
series of belt conveyors to spreader.
34. G Contd.
G. Main mining equipment
5)Rock breaker technology:
• Rock breaker technology can be applied for breaking of rock/coal/ore
even about 500 kg/sq.cm.
• It can be used wherever it is not possible to go for blasting – near
vicinity of structures and habitations.
6)Surface Miner Technology:
•Used for selective mining.
•Larger strike length of about 600 m – 1000 m and widths of around
300 m are ideally suited for surface miner.
•Does not need drilling and blasting. The machine cuts the coal &
loads into trucks for onward transportation to Surface
Other common mining equipment to all the technologies
•Drills
•Dozers ,Graders & Compactors
•Water Sprinklers
•Pumps etc.
•Electrical equipment
•Crushers & Conveyors for Coal/OB
41. H. Dumping strategy and balancing
Internal dumping:
Depends on the steepness of the seams.
As the gradient increases, the percentage of dumping reduces.
Internal dumping can be increased by sectorial working of the pit – which may
reduce the annual output.
Toe of the dump generally kept at a distance of 100 m from the working benches.
Floor of the pit to be roughened by blasting for increasing dump stability.
General design of dumps:
• Deck height – 30m
• Berm width – 30m
• Deck slope – 37½0
• Overall slope – 280
• Swell factor for OB-1.38,for coal –1.40
• Swell compact after initial settling – 1.20
Note:-Dump yard management and control is essential for the success of open cast
mining. In case of more than one External Dump yards, balancing the excavation
volume to either of the dump yard should be based on lead & lift and size of the
Dump yards.
42. H Contd.
H. Dumping strategy
1. Total dump height- 90m
1. Total dump height- 90m
2. Deck height – 30m
2. Deck height – 30m
3. Berm width – 30m
3. Berm width – 30m
4. Deck slope-37 ½ 0
4. Deck slope-37 ½ 0
5. Overall slope-280
5. Overall slope-280
43. H Contd.
H. Dumping strategy
1. Total dump height- 90m
1. Total dump height- 90m
2. Deck height – 15m
2. Deck height – 15m
3. Berm width – 15m
3. Berm width – 15m
4. Deck slope-37 ½ 0
4. Deck slope-37 ½ 0
5. Overall slope-24.830
5. Overall slope-24.830
44. H Contd.
Internal Dumping reduces with the increase in the gradient of the seam.
Comparison between 1in4 and 1in8 Gradient
floor dipping at 1in4 floor dipping at 1in8
Assumptions:
Strike Length : 1000m
Max. Depth : 110m
Coal Seam thickness : 15m
Annual Rated capasity : 6.0 LTPA
Project Parameters 1in4 1in8
Area of Excavation : 0.59 Sq.km 1.04 Sq.km
Mineable Reserves : 90.0 L.T 180.L.T
Total OB Removal : 274.0 L.m3 480.5 L.m3
Stripping Ratio : 2.74 2.67
Life of the Project : 17 Years 32 Years
Volume of Internal Dumping : 39.85 L.m3 256.41 L.m3
Volume of External Dumping : 234.15 L.m3 134.00 L.m3
% of Internal Dumping : 14.54 53.36
(upto Ground Level)
Safe distance from coal bench
to toe of internal dump : 100m 50m
45. I. Designing the year-wise / stage – wise plans
I) Stage plans
• Stage plans are prepared based on Year-wise production
requirements (rated out put)
• Stage plans at the end of years – 1, 2, 3, 4, 5 & in intervals of 5
years are prepared.
• Also plans are prepared where any specific land mark like a new
box-cut, change in layout will take place.
46. J. Financial Viability
1) The requirement of HEMM & its capital is estimated.
2) Other capital like developmental works, CHP etc are worked
out.
3) Operating expenses are worked out to arrive at cost of
production.
4) Financial viability including profit & loss , IRR etc is
estimated.
5) Based on required IRR, anticipated selling price is also
worked out.
47. K. Coal Washing
Need for Washing
Power Houses consume about 75% of coal.
Power Houses are designed to accept Coal of ‘E’ Grade & above
(UHV>3300).
The percentage of production of coal below ‘E’ Grade is increasing .
MoEF stipulation – Presently the onus of responsibility is on end user for
using Coal of not more than 34% ash if he is located over 1000Km away.
Hence, the need to upgrade coals below ‘E’ Grade so as to suit the
requirements of Power houses.
Cost of washing is around Rs 120-130/T of raw coal.
48. L. Environment stipulations
As per EP Act 1986
“Environment”
includes water, air and land and the inter-relationship
which exists among and between water, air and land and
human beings, other living creatures, plants, micro
organism and property
49. L Contd.
Impacts and Mitigative Measures
• Air
– Impacts: Dust is generated from drilling, blasting,
excavation, crushing and transportation operations. This
dust becomes air borne and gets carried away to
surrounding areas.
– Mitigative Measures:
• Extensive water spray arrangements at the Coal
handling sites.
• Wet-drilling methods are to be adopted.
• Water spraying on haul roads and permanent transport
routes at required frequencies. Provision for mobile
water sprinklers has to be made for this purpose.
• Extensive Green Belt development around the quarry
and OB dump
• Black topping the transport routes and avenue
plantation on these roads.
52. L Contd.
Impacts and Mitigative Measures
• Water:
– Impacts:
• Pollution of the surface water bodies with the
mine discharge water and domestic sewage.
– Mitigative Measures:
• The Mine Discharge water is to be treated in
settling tanks before discharging it into the
surface water bodies.
• Effluent from workshop is to be treated in ETPs.
• Sewerage treatment plant to be provided for
treating the domestic sewage from the colony.
55. Impacts and Mitigative Measures L Contd.
Noise Pollution & Vibrations
• Impact
− The main sources of noise in the project are electrical and
diesel-powered machines, compressors, pumps, drilling
machines, dumpers, etc.
− During blasting operations blast vibrations will take place.
• Control Measures
– Controlled blasting techniques using NONELs are to be
adopted .
– Creation of green belts of dense foliage in three rows
between mine areas and residential colonies.
– Proper maintenance of machinery including transport
vehicles.
– Protective devices like earplugs and earmuffs are to be
provided to the needy workers.
– Sound and dust proof cabins are to be provided in the
machines like dozers, shovels, dumpers and feeder
breakers at CHP etc.
56. Impacts and Mitigative Measures L Contd.
Over Burden Management
Topsoil excavated from the quarry is to be dumped
separately at predetermined place and has to be
subsequently spread on external dumps for plantation.
Top soil dump is to be kept not more than 10m height.
Top soil has to be vegetated with grasses and
leguminous species to maintain its fertility.
The reclamation of O.B dumps is to be done by using
Biological Engineering techniques for stability of slopes
and prevention of soil erosion from O.B dumps.
Construction of crib structures, Gabion structures,
forming of staggered Contour trenches are to be
practiced for stability of slopes.
57. L Contd.
Impacts and Mitigative Measures
Over Burden Management
Raising of seedlings on both top and slopes of the dumps
in the staggered contour trenches.
By dibbling seeds of various species like Avisa, Subabool,
Babul, Neem etc.
Safe disposal of rainwater by construction of garland
drains. Garland drains are to be provided around the
quarry and overburden dumps .
