&
Geotechnical Studies for Introducing High Capacity
Longwalls and Longwall Top Coal Caving Mining in
SCCL – A Case Study
4th Coal Summit, New Delhi
J.V. Dattatreyulu*, Manoj Khanal #, Deepak Adhikary #, Rao Balusu #
*The Singareni Collieries Company Limited, Andhra Pradesh, India
#CSIRO Earth Science and Resource Engineering, 4069 Queensland, Australia
J. V. Dattatreyulu
Dir (Operations), SCCL
2
Overview
• Reserve scenario
• Limitations of present technology
– Financial aspects
• Suitable technology
• Cost comparison between OC&LW
• SCCL LW projections
• Strategy
• Reserve Scenario
• Proved Indian Coal Reserves (as on 01.04.2012 as per CMPDI)
• Total Proved Reserves
: 118144 MT
• Reserves in depth range of 300-600m (UG) : 10423 MT (09%)
•
(excluding Jharia)
• Reserves in depth range 0-300m (OC)
•
: 92251 MT (78%)
(excluding Jharia)
• Reserves in Jharia depth range 0-600m
: 13710 MT (11.6%)
• Proved Coal Reserves – SCCL (as on 31.03.2012)
• Total Reserves
• Sterilised Reserves (including Operating mines)
• Balance In-situ UG Reserves (300-600)
• Balance In-situ OC Reserves (0-300)
:9877 MT
:4408 MT
:3362 MT (61.5 %)
:2107 MT (38.5%)

Opencastable reserves lasts longer in CIL contrary to SCCL

Considerable Reserves present beyond 300m depth are to be exploited by
UG mining
Limitations of Present Technology
 SDL/LHD
 Applicability
SDL - gradient 1 in 4 & flatter
LHD - gradient 1 in 6 & flatter
 Less production and productivity levels & Less feasibility of quantum jump in
production - Average Production per SDL &LHD : 45000 TPA & 1.0 LTPA
 High cost of production - Avg. Cost of Production at SCCL (Rs/T) : 3000
Blasting gallery
Limited Applicability - thick and easily cavable seams of gradient 1 in 6 & flatter
 Continuous Miner
Limited Applicability - gradient 1 in 8 & flatter
Average production levels around 0.5MTPA per CM
Long wall




Suitable for the property devoid of faults
any gradient
any thickness
Even at greater depths
Limitations of Present Technology
Contd…..
• Reserves beyond 300 m depth line also associated with Complex
geological conditions like increased stress concentration zones, weak
roof, steep gradients etc.
• The present method of pillar formation may not be stable at greater
depths

Hence we need

The Cutting technology capable of working at greater depths with
safety, Negotiate steep gradients and can handle the adverse geomining conditions
TECHNOLOGY
COST OF PRODUCTION
(Rs/Tonne)
2012-13 (Sep)
2011-12
Hand Section
6387
5379
Long wall
3513
2451
Side Discharge Loaders
3214
3258
Load Haul Dumpers
2986
3284
Blasting Gallery
1895
1976
Continuous Miner
1759
2096
Overall SCCL (UG)
3272
3372
Overall SCCL (OC)
1368
1229
Overall SCCL
1911
1697
(Avg. Sales Realization /Tonne during 2012-13 &2011-12 is Rs. 1860 and 1709
respectively.
Contd…..
EMS, OMS & % Increase - UG MINES
YEAR
2008-09
1149.06
2009-10
1186.72
3.28
0.91
-2.15
0.78
2010-11
1476.16
24.39
0.99
8.79
0.77
2011-12
1982.04
34.27
1.01
2.02
0.75
2012-13
(Sept)
2141.00
8.02
1.09
7.92
Not
Available
17.20
--
Overall % Change
%
Increase
%
Increase
EMS
(Rs)
OMS
0.93
86.33
OMS of
CIL
0.76
9
% CHANGE in EMS & OMS
Financial Aspects - Cost of Production
• Exploitation of For deeper deposits involves
 Increased infrastructural requirements in terms of
 Long/Deeper tunnels/shafts
 Ventilation
 Pumping
 Transportation of Coal, men and material etc.
• Hence high Cost of development and out bye
infrastructural arrangements
• High capital investments results in high cost of production
• The technology should offset the heavy investments/high operating
cost and should yield required financial viability
• This
necessitates
technology
UG
mass
production
Suitable Technology
•The required technology should give
•Mass Production
•Safe Operation
•Suitable to operate at greater depths beyond 300m
• and shall be a Proven Technology

The technology proven around the world (like China &
other major coal producing countries) with high
production levels compatible with Opencast mining is
Longwall
Comparison of Cost of production OC & LW
(as per SCCL estimates)
• Opencast Mine (Calculated as per the SCCL Financial results of Ist half of
2012- 13)

The present stripping ratio

OB removal cost
- 6.5

Company
`/Cum - 171

Outsourcing `/Cum -

With 30:70 ratio of company & Outsourcing operations, the
Cost of OB removal is `/Cum
- 105
77

The cost of 6.5 Cum OB removal `
A=6.5X105 = 682.5

Cost of production of coal `/T
B=200

Overhead cost @ 15% of total cost `/T =0.15X(A+B)=132.4

Total cost of production `/T
=1015
Cost Comparison
Contd……
• Long wall Cost of Production
As per the FR of Adriala Project of SCCL @85% performance level (Oct2012)
 Total Capital required for the project
- around ` 995 Cr
 Capital required for Longwall equipment - around ` 414 Cr
 Production
-2.4MTPA (2.8 @100%)
 The Cost of Production per tonne
- ` 1240 .
• Difference of COP between OC & LW `/T =1240-1015
=225

• Additional costs involved in OC Projects
– Backfilling cost - around 150 ` /T
– NPV per Ha for UG &OC is 50% & 100%
respectively
• Avg. cost including CA land & charges for UG
& OC - (` /Ha) 3.13 Lakhs & 11 Lakhs
respectively
Long wall Projections at SCCL
• Project
Capacity (MTPA)
• KLP (TPO)
2.747
• Shanthikhani
1.17
• KK-7 Incline
1.50
• RKP Shaft block – 1& 2
2.00
• KTK-3 Incline
1.50
STRATEGY
• Demarcating the Coal reserves up to 300m depth for
Opencast mining (Conservation as the primary concern)

Establishing the mass production underground
technology for the reserves beyond 300m depth

Devising & Enforcing a National policy for

Exploitation of deep seated reserves concurrently with OC
production

Providing encouraging atmosphere for the establishment of
LW Equipment manufacturing facility/services in India by
starting number of projects in CIL & SCCL
Geotechnical Studies for Introducing High Capacity
Longwalls and Longwall Top Coal Caving Mining
in SCCL – A Case Study
Manoj Khanal
Objective
• To assess the feasibility of introducing high capacity
longwalls and LTCC mining at Adriayala mining block in
SCCL using comprehensive analysis of geological and
geophysical mine data, empirical and numerical
approaches.
Approach
• Site investigations and characterization studies at mine sites -
Collection of
geological and geomechanical SCCL data (existing and new data), - field monitoring,
measurements and laboratory investigations
• Analysis of SCCL data
• Extensive integrated computational simulations
- Development of 3D
geotechnical model
• Assessment of introducing high capacity longwall
• Prefeasibility study of LTCC mining at Adriyala block through
• Empirical approach and
• Extensive numerical modelling
SCCL Mine
•Proven coal reserves 8791Mt.
•Currently 15 OC and 35 UG mines
•Produced ~53 Mt of coal in 2011/12.
•In Ramagundam region of SCCL, 4
mineable seams:
I seam (Top) (thickness varies from 2-5.5m)
II seam (thickness varies from 2-5.5m)
III seam (avg. thickness varies from 8-10m)
IV seam (Bottom) (thickness varies from 2-5.5m)
Singareni mines – The field mine sites of
this project GDK 9, 10 and 10A mines
complex and their extension mining
blocks are located in Ramagundam /
Godavari Khani area – around 200 km
from Hyderabad
and additional three thin seams
IA, IIIB, IIIA
are consistent over many kilometres.
Currently, SCCL uses bord and pillar method involving two sections and Blasting Gallery method to extract thick seam (III Seam).
High Capacity Longwalls
•Currently, SCCL uses longwall width – 150 m (circa)
Example, Australian longwall production
•Current trend - production of 3MT to 5MT per year.
•Level of productivity is influenced by - face width, cutting height, mining depth
•Above average performance indicates possible favourable mining conditions
Longwall Top Coal Caving Method
•SCCL, Longwall Top Coal Caving Method – conducted a prefeasibility study
Example, Chinese longwall top coal caving production
•China uses LTCC
•Extract thick seams up to 12m
•For soft and hard coal
•A cost effective mechanism as the shearer slices only the bottom part of the
seam and the top coal fractures due to gravity. The only additional cost will be
added to the rear conveyor and modification of the chocks of the normal
longwall equipment
Ref: Peng SS, Chiang HS. Longwall mining. New York: Wiley. 1983; Cai Y, Hebblewhite BK, Onder U, Xu B, Kelly M, Wright B, Kraemer M. Application of longwall top coal caving to Australian
operations. CSIRO‐ACARP report C11040. 2003; Xie H, Chen Z, Wang J. Three dimensional numerical analysis of deformation and failure during top coal caving. International Journal of Rock
Mechanics and Mining Sciences. 1999, 36:551‐558.
Longwall Top Coal Caving Method
For Adriyala – Seam III – average seam thickness of 8m - 10m
Parameters affecting LTCC
Intrinsic
thickness of coal seam, coal strength and deformation properties, inclination of coal
seam, roof sandstone strength and deformation properties and coal geology
Non‐intrinsic
existing equipment support for normal longwall extraction, life of the mine, financial
health of the mine and a detailed geological study of the mine.
Efficient implementation of the LTCC may be achieved through:
•past experience of mining in identical geological and excavation situations
OR
•detailed assessment using most up to date analysis method
Steps followed
1. Site Data Collection and Interpretation
Development of a comprehensive geological and geotechnical model
2. High Capacity Longwall Study
3. Prefeasibility study of LTCC
•
Empirical Assessment of LTCC
•
Numerical Simulation of LTCC
To investigate chock loading behavior, strata caving mechanism,
top coal fracturing mechanism, abutment stress, vertical stress etc.
1. Site Data Collection and Interpretation
1. Topography and 3D stratigraphic units
Lithological/geophysical description by
•Core logging
•Geophysical logging (with proper depth
correction)
2. Geological structures
Detection of structural features and their
orientation through core logging,
geophysical logging and seismic survey
•Cleats
•Bedding planes
•Faults/folds
•Joints
•Fracture planes
•Shear zones
•Intrusions
3. Physical and mechanical properties
•Strength properties (dry and saturated
conditions)
•Elastic properties
•Scale effects
•Time dependency
•Physical properties (eg, density, porosity,
etc)
4. Hydrogeological properties
•Local hydrology
•Ground water level/phreatic surface
•Aquifers/aquicludes
•Permability
•Pore water pressure
5. In situ stresses
•Magnitude and direction
1. Site Data Collection and Interpretation
• Field site - 10 and 10A mines and
their extension mining blocks
(Adriyala)
•First pass geological model –
developed using available
geological data from a total of 265
boreholes
•Integrated geological model - the
initial geological model - refined with
the results from detailed analysis of
geophysical data from 10 newly
drilled holes.
Map showing the location of exploration data integrated into geological model
1. Site Data Collection and Interpretation
• New wireline logging data reliably allowed
•the identification of all rock types resulting in the subdivision of
several interburden units into separate sandstone units.
•the detailed mapping of potential weak planes, such as presented by
thin siderite bands or abrupt changes in rock type (bedding planes) in
the rock mass, which are critical from caving point of view.
1. Site Data Collection and Interpretation
Integrated geological model
• Requirement were for more detailed rock mass characterisation in the
roof and interburden strata around coal seams
The challenge was to:
• subdivide the interburden sandstone units into coherent rock types that may be
related to consistent geotechnical properties and
• identify major bedding planes that have the potential to shear or separate during
mining.
• Tool for this analysis - fence diagram that compiles all the boreholes
with wireline log data on a single section
• A detailed integrated geological model was then developed using
LOGTRANS and SOM for Adriyala mining block
1. Site Data Collection and Interpretation
Integrated geological model
A typical screen snapshot of the integrated geological model
1. Site Data Collection and Interpretation
Various strata on the site
Longwalls
For LTCC -Thickness of SS40, SS50 and SS60
In situ stress measurement
• A total of 17 successful fluid injection tests
were conducted by MeSy India (2006) at
site 1205 of the Adriyala Long Wall Block at
depths between 77 m and 522 m. The
orientation of the induced fractures was
determined by impression packer tests.
The mean azimuth of the vertical fractures
was determined as N (24 ± 14) degrees
(NNE). The minor and major horizontal
stresses are:
sh, MPa = 2.05 + 0.0092 · (z,m - 77)
sH, MPa = 3.13 + 0.0142 · (z,m - 77)
0
sandstone
coal
100
1205D
200
depth, m
• 17 hydrofrac tests and 13
additional hydraulic tests.
• The permeability apparently
decreases with depth and
• The permeability value ranges from
10 to 103 µDarcy
300
1205R
400
500
1205
600
0
10
1
10
2
3
10
10
permeability, µDarcy
4
10
5
10
2. High Capacity Longwall
• Numerical code developed by CSIRO - COSFLOW
• Designed to run on a large number of parallel computers
• Typically, two panel model 1.5 million elements with 32
processors took up to 8 to 10 weeks of computing
COSFLOW mesh
COSFLOW validation
30.00
25.00
761.2
570m 555m
210m 200m
782
Stress (MPa)
4 x 800 T chock- shield support
20.00
792.4
802.8
813.2
823.6
15.00
834
844.4
Location 737m
Location 717m
10.00
Location 727m
Location 730m
GOAF
LW Panel No. 3A
Stress (MPa)
771.6
LO L
O
= 150 m
O
750.8
Face length
O
FACE RETREAT
500 m
Barrier Pillar
75 m
200 m
Face gradient
1 in 20
Retreat gradient 1 in 6
Tail Gate
640m
Location 710m
Location 720m
5.00
0.00
0
10
20
30
40
50
60
Distance from face (m)
Total length = 1075 m
Gate road height = 3.3 m
Gate road width = 4.2 m
O
640m
O
Main Gate
515 m
L
O
200 m
O
Load cells
L
72.5 m
90
Location 750m
Barrier Pillar
Multi-point extensometer from surface
L - Load
cell (to be shifted at every 10 m)
Location 800m
70
Not to scale
Displacement (mm)
O Tell Tale extensometer
80
COSFLOW
prediction
60
50
40
30
20
10
0
0
10
20
30
Distance from face (m)
Tell Tale
40
50
2. High Capacity Longwall
Modelled cases –100,160,200 and 260m wide longwall panels – 800 and
1100t capacity chocks
2. High Capacity Longwall
50
1100t
800t
500t
Convergence (mm)
45
40
35
30
25
Face Position (m)
250m wide panel – Chock convergence
Convergence - 1100t - 200 m wide panel
2. High Capacity Longwall
Caving/fracturing of SS80 and SS100 (250m wide panel) at various steps
3. Prefeasibility Study of LTCC (Empirical Assessment, 2 Indices)
Chinese Index (according to Chinese experience - affecting
parameters - top coal thickness, stone band thickness, degree of
coal fracture, and immediate roof thickness)
Using numerical simulations and regression analysis, CI (y)
Parameters
Thickness
Dipping at
Seam depth
UCS
Coal fracture index
Stone band thickness
Top coal thickness
10m
8 to 10deg
300 to 400 m
25.5 MPa
0.3
0.1
7m
Caving index = 0.84 to 0.91
(for depths between 300 m and 400 m)
Classification 2 = "good“
(predicted coal recovery of about 70 to 80 %)
Ref: Zhong MJ. Theory and technology of top coal caving mining. China Coal Industry Publishing House. 2001.
3. Prefeasibility Study of LTCC (Empirical Assessment, 2 Indices)
CSIRO Index (according to CSIRO experience - affecting
parameters - depth of mining, coal strength and top coal
thickness)
Using numerical simulations, CI
Parameters
Thickness
Dipping at
Seam depth
UCS
Coal fracture index
Stone band thickness
Top coal thickness
10m
8 to 10deg
300 to 400 m
25.5 MPa
0.3
0.1
7m
Caving index = -7.5 to -3.5
(for depths between 300 m and 400 m)
Classification = "good to moderate“
(predicted coal recovery of about 56 to 67 %)
Humphreys P, Poulsen B. BMA‐Geological Assessment and Numerical Modelling of LTCC, CSIRO Report. 2008.
A typical COSFLOW mesh
Plan area
Finite Element
9km2
1.5 M
Plan view
Chocks
Roller boundaries
Free surface
Initial stress filed
fine mesh area
4 sides + base
Top surface
In-situ stress*
Oblique view
*MeSy (India) Pvt. Ltd. In‐Situ Stress and Permeability Measurements in Boreholes in the KTK.3 Incline Dipside Block and in the KTK. Longwall Block of Bhupalpalli Area of the Mulug Coal Belt
of Warangal District, Andra Pradesh, Report no. SCCL_01/08. 2008.
Model Variation
•Effects of variation on the strength properties of SS40 (main roof), SS50 and
coal seams various cases were modelled.
•Explicit planes of weaknesses were introduced in‐between SS40 and IIIA, and
IIIA and SS50.
Chock Convergence
Comparison of convergence at three different places along the mine width
(1100t capacity support)
Chock Convergence
Chock convergence for Case1 (all SS massive) and Case4 (SS40 layered) - 1100t
capacity support
Strata Caving Behaviour
Fracture of different layers of SS80 and SS100 for Case6
Top Coal Caving Behaviour
Step C = 0.8m behind the when the
face of the chock is at 598m from
the start line
Step D = 0.8m ahead the when the
face of the chock is at 598m from
the start line
Fractured Intact
Step E = 2.4m behind the when the
face of the chock is at 598m from
the start line
Top coal yield at different distances from the face for Case8
Vertical Stress
Vertical stress for 250m wide panel for Case1 at the middle of bottom and top coal
layers, 630m after retreat
Limitation of numerical modelling
• Numerical code being static one does not considers the time
effect on deformation
• COSFLOW results obtained from a numerical model could be
viewed as a scenario when the chocks are subjected to roof
strata loading for hours
Conclusions
•Demonstrated a various steps involved in investigating the
feasibility of LTCC mining method in one of the mines at SCCL.
•Various factors affecting the LTCC behavior were considered and
evaluated in order to assess the feasibility of LTCC method.
•The study undertook a comprehensive analysis of geological and
geophysical data of the mine site and developed detailed
geotechnical frameworks for the assessment of LTCC technology.
•The paper also showed various parameters which are to be
evaluated in order to gain confidence and implement LTCC at the
SCCL mine site.