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BULK PRODUCTION TECHNOLOGY THE OPTION FOR UNDERGROUND MINING. &. Geotechnical Studies for Introducing High Capacity Longwalls and Longwall Top Coal Caving Mining in SCCL – A Case Study. 4 th Coal Summit, New Delhi. J.V. Dattatreyulu *, Manoj Khanal # , Deepak Adhikary # , Rao Balusu #.

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Geotechnical Studies for Introducing High Capacity Longwalls and Longwall Top Coal Caving Mining in SCCL – A Case Stud

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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

bulk production technology the option for underground mining

J. V. Dattatreyulu

Dir (Operations), SCCL

  • 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 Jhariadepth range 0-600m : 13710 MT (11.6%)
  • Proved Coal Reserves – SCCL (as on 31.03.2012)
    • Total Reserves :9877 MT
    • Sterilised Reserves (including Operating mines) :4408 MT
    • Balance In-situ UG Reserves (300-600) :3362 MT (61.5 %)
    • Balance In-situ OC Reserves (0-300) :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


    • 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

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 geo- mining conditions

Limitations of Present Technology Contd…..


Financial Aspects

Technology wise Cop at SCCL

(Avg. Sales Realization /Tonne during 2012-13 &2011-12 is Rs. 1860 and 1709 respectively.

financial aspects cost of production

Financial Aspects - Cost of Production

Exploitation of For deeper deposits involves

Increased infrastructural requirements in terms of

Long/Deeper tunnels/shafts



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 UG mass production technology

suitable technology

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


comparison of cost of production oc lw as per sccl estimates
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 - 6.5
      • OB removal cost
        • Company `/Cum - 171
        • Outsourcing `/Cum - 77
        • With 30:70 ratio of company & Outsourcing operations, the Cost of OB removal is `/Cum - 105
      • 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
Cost Comparison Contd……
  • Long wall Cost of Production
        • As per the FR of Adriala Project of SCCL @85% performance level (Oct-2012)
          • 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 Lakhsrespectively
long wall projections at sccl
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
  • 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




  • 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.


  • 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

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


  • 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)
  • and additional three thin seams
  • 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

  • 3. Physical and mechanical properties
  • Strength properties (dry and saturated conditions)
  • Elastic properties
  • Scale effects
  • Time dependency
  • Physical properties (eg, density, porosity, etc)
  • 1. Topography and 3D stratigraphicunits
  • 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
  • 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



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)

  • 17 hydrofrac tests and 13 additional hydraulic tests.
  • The permeability apparently decreases with depth and
  • The permeability value ranges from 10 to 103 µDarcy

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



Stress (MPa)

COSFLOW validation

Load cells

Tell Tale


2. High Capacity Longwall

Modelled cases –100,160,200 and 260m wide longwall panels – 800 and 1100t capacity chocks


2. High Capacity Longwall

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)


Thickness 10m

Dipping at 8 to 10deg

Seam depth 300 to 400 m

UCS 25.5 MPa

Coal fracture index 0.3

Stone band thickness 0.1

Top coal thickness 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


Thickness 10m

Dipping at 8 to 10deg

Seam depth 300 to 400 m

UCS 25.5 MPa

Coal fracture index 0.3

Stone band thickness 0.1

Top coal thickness 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 9km2

Finite Element 1.5 M

Plan view

Chocks fine mesh area

Roller boundaries 4 sides + base

Free surface Top surface

Initial stress filed 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

Step E = 2.4m behind the when the face of the chock is at 598m from the start line

Fractured Intact

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


  • 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.