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

&

BULK PRODUCTION

TECHNOLOGY THE OPTION FOR UNDERGROUND MINING

2

J. V. DattatreyuluDir (Operations), SCCL

Overview

• Reserve scenario

• Limitations of present technology

– Financial aspects

• Suitable technology

• Cost comparison between OC&LW

• SCCL LW projections

• Strategy

• 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 :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

• Reserve Scenario

Limitations of Present Technology SDL/LHD

Applicability SDL - gradient 1 in 4 & flatterLHD - 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 geo-

mining 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

Financial AspectsTechnology wise Cop at SCCL

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

respectively.

Technology wise Cost of production

9

EMS, OMS & % Increase - UG MINES

YEAREMS (Rs)

% Increase

OMS%

IncreaseOMS of

CIL

2008-09 1149.06   0.93   0.76

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

Overall % Change 86.33 17.20 --

Financial aspects Contd…..

% 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 UG mass production 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 TechnologyThe 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 - 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……

• 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 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 depthDevising & 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

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 seamsIA, IIIB, IIIA are consistent over many kilometres.

SCCL Mine

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 LTCCIntrinsic

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. Topography and 3D stratigraphic unitsLithological/geophysical description by

•Core logging•Geophysical logging (with proper depth correction)

1. Site Data Collection and Interpretation

2. Geological structuresDetection 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 5. In situ stresses

•Magnitude and direction

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

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.

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 model1. Site Data Collection and Interpretation

A typical screen snapshot of the integrated geological model

1. Site Data Collection and InterpretationVarious strata on the site

Longwalls

For LTCC -Thickness of SS40, SS50 and SS60

• 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)

In situ stress measurement

0

100

200

300

400

500

600

d ep t

h , m

100

101

102

103

104

105

permeability, µDarcy

sandstonecoal

1205

1205D

1205R

• 17 hydrofrac tests and 13 additional hydraulic tests.

• The permeability apparently decreases with depth and

• The permeability value ranges from 10 to 103 µDarcy

• 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

2. High Capacity Longwall

COSFLOW mesh

4 x

800

T c

hock

-shi

eld

supp

ort

Face

leng

th

=

150

m

72.5 m200 m515 m

Not to scale

Face

gra

dien

t

1 in

20

Retr

eat g

radi

ent

1 in

6

O Tell Tale extensometer

Total length = 1075 mGate road height = 3.3 mGate road width = 4.2 m

G O

A F

FACE

R

ETRE

ATBarrier Pillar

Barrier Pillar

LW Panel No. 3A

Tail Gate

Main Gate

500 m 200 m 75 m

O

O O

O

O

O

Multi-point extensometer from surface

L - Load cell (to be shifted at every 10 m)

L L

LL

570m 200m

O

O640m

640m

555m 210m

COSFLOW validation

0.00

5.00

10.00

15.00

20.00

25.00

30.00

0 10 20 30 40 50 60

Distance from face (m)

Str

ess

(MP

a)

750.8

761.2

771.6

782

792.4

802.8

813.2

823.6

834

844.4

Location 737m

Location 717m

Location 727m

Location 730m

Location 710m

Location 720m

Str

ess

(MP

a)

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50

Distance from face (m)

Dis

pla

cem

en

t (m

m)

Location 750m

Location 800m

COSFLOWprediction

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

25

30

35

40

45

50

Face Position (m)

Co

nverg

en

ce (

mm

)

1100t 800t 500t

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)

Ref: Zhong MJ. Theory and technology of top coal caving mining. China Coal Industry Publishing House. 2001.

ParametersThickness 10mDipping at 8 to 10deg Seam depth 300 to 400 mUCS 25.5 MPaCoal fracture index 0.3Stone band thickness 0.1Top 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 %)

CSIRO Index (according to CSIRO experience - affecting parameters - depth of mining, coal strength and top coal thickness)

Using numerical simulations, CI

ParametersThickness 10mDipping at 8 to 10deg Seam depth 300 to 400 mUCS 25.5 MPaCoal fracture index 0.3Stone band thickness 0.1Top 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.

3. Prefeasibility Study of LTCC (Empirical Assessment, 2 Indices)

A typical COSFLOW meshPlan area 9km2

Finite Element 1.5 M

Chocks fine mesh areaRoller boundaries 4 sides + baseFree surface Top surfaceInitial stress filed In-situ stress*

Plan view

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

Top coal yield at different distances from the face for Case8

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 lineFractured Intact

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.

Thank You