ausrock2014 - 5/6th november coalmine pillar design and ... · 6 ecl sarpi joy r -vii 4.0 5.5 120...

Coalmine Pillar Design and Performance

During Mechanised Pillar Extraction in

India

AusRock2014 - 5/6th November

Keith MacAndrew

Alex Garcia

Ian Gregson

5

8

12

15

6m

17

16

14

13 6

7

10

9

11

5

5 8

5 12

15 1

3

26

m

2

4

SPLIT AND FENDER

15

32m pillar centres

(26 m pillars)

32 m

Indian Coal Background

November 14, 2014 2

India is the 3rd largest coal producer in the World (530mt/annum).

India has the 4th largest coal reserves in the World (approx. 277bt).

Almost 90% of India’s coal production is accounted for by surface

operations. Underground mining is now being expanded due to near surface

deposits and environmental restrictions (afforestation).

India imports over 200mt of coal per annum.

India has the 2nd largest population in the World after China (1.25 billion).

It is expected to increase its current annual consumption of coal from 770mt

to 1.5bt per annum by 2030 (with 400mt/annum imported). This will require

India to at least double its annual production in the next 20 years. To meet

this projected coal demand, India is looking to highly mechanised

underground mining.

Golder in India

November 14, 2014 3

Rock Mechanics Technology (RMT - now Golder) was formed following the

privatisation of the Rock Mechanics Department of British Coal in 1994 and

were instrumental in the successful introduction of rockbolting in to the UK

coal mining industry, to replace standing steel support (At the time, this

method of support was outside of the current legislation and was closely

supervised by the UK Mines Inspectorate).

The Indian Mines Inspectorate, DGMS, recognised Golder (formally RMT -

1997) as having the appropriate technology and expertise to introduce

improved support and mining methods that would enable the introduction of

mechanised mining in a safe and controlled manner.

With this recognition by the DGMS, Joy Mining Machinery (UK) identified

RMT (now Golder) as the facilitator to open up the vast potential market for

their high performance continuous miners in India.

Golder Projects in India

November 14, 2014 4

Golder currently have 5 projects with JMS

(Joy Machinery).

Plus 2 similar projects with Tractor India

(Caterpillar Equipment).

Two of the World’s largest equipment

suppliers.

Many more projects in the pipeline.

These projects were originally with Joy

Mining and Caterpillar equipment.

Joy and Caterpillar wanted to reduce their

risk and supply equipment only.

Both Joy and Caterpillar have transferred

their contract mining services to JMSL and

Tractor India Private Limited respectively.


November 14, 2014 5

SITE AREA Mine CM Operator Seam Thickness

(m) Depth

(m)

Entr

y W

idth

(m

)

Entr

y H

eig

ht

(m)

Pill

ar C

en

tre

s (m

)

Bo

lt L

en

gth

(m

)

Bo

lt D

en

sity

(b

/m2 )

De

velo

p-m

en

t

Re

-De

velo

pm

en

t

Pill

ar E

xtra

ctio

n

Me

tho

d

De

gre

e o

f C

ave

abili

ty

1 SECL NCPH (2) JOY No.5 3.3.3.8 80 - 150 5.8 3.3 - 3.8

35 1.8 0.46 YES NO Split and Fender

Moderate to Difficult

2 WCL Tandsi II

Declines 3/4 JOY No.3 3 - 4.5 190 - 370 4.8 4 - 3.5 40 2.4 2.1 YES NO

Split and Fender

Easy

3 SCCL **VK7 JOY King 6.0 - 7.0 330 - 410 6 4.6 45 1.5 0.56 YES YES 1/3 Split and

Fender

Difficult to

Moderate

4 SCCL GDK 11 CATERPILLAR No.1 4.5 - 6.3 250 - 350 6 3.6 47 1.8 0.46 YES YES Double Split and Fender

Moderate to Difficult

5 ECL Jhanjra I JOY R-VI 4.0 - 4.5 110 - 140 6 4 - 4.3 32 1.5 0.56 YES NO Split and Fender

Difficult to

Moderate

6 ECL Sarpi JOY R-VII 4.0 - 5.5 120 - 210 6 4 - 4.5 34 1.8 0.56 YES NO * Split and

Fender Easy to

Moderate

7 SECL Sheetaldhara JOY No.3 ( C ) 3.5 - 4.5 160 - 190 6 3.5 35 1.5 0.66 YES YES Split and Fender

Easy

8 SECL ****Pinoura CATERPILLAR LB-1 3.5-4.5 65-135 6.5 3 21 - 26 1.8 0.89 YES YES Herring

Bone/Fish Tail

Easy

9 ECL ***Jhanjra II CATERPILLAR R-VI 2.5 - 3.5 130 - 310 6 3 - 3.5 30 to

38 2.1 0.56 YES NO

Split and Fender

Difficult to

Moderate

** VK7 - Due to caving issues an alternative Yield Pillar pillar extraction method was adopted but has recently been replaced by the 1/3 split and fender method.

*** Jhanjra II project is due to start production in the spring of 2014.

**** Pinoura Mine - Golder have had no involvement at this site.


November 14, 2014 6

SITE AREA MineCM

OperatorSeam

Thickness

(m)

Depth

(m)

En

try

Wid

th (

m)

En

try

He

igh

t (m

)

Pil

lar

Ce

ntr

es

(m)

Bo

lt L

en

gth

(m

)

Bo

lt D

en

sity

(b/m

2)

De

ve

lop

me

nt

Re

-

De

ve

lop

me

nt

Pil

lar

Ex

tra

ctio

n

Me

tho

d

De

gre

e o

f

Ca

ve

ab

ilit

y

Op

era

tio

na

l

Sta

tus

Anjan Hill Zero 3.5 - 4.5 5 - 150 5.2 3 - 4.5 35 2.4 0.51 YES NOSplit and

Fender

Easy to

Moderat

e

Exhausted

NCPH No.5 3.3 - 3.8 80 - 150 5.8 3.3 - 3.8 35 1.8 0.46 YES NO No

Moderat

e to

Difficult

Exhausted

R6 No.3 6.5 30 - 80 5.5

4m + 1m

bottom

coaling

22 1.8 0.49 YES NOModified

NEVID

Difficult

to

Moderat

e

Exhausted

NCPH (2) No.5 3.3.3.8 80 - 150 5.8 3.3 - 3.8 35 1.8 0.46 YES NOSplit and

Fender

Moderat

e to

Difficult

Working

*Kapildhara No.3 3.0 - 4.5 20 - 50 6 3.5 20 2.4 0.56 NO YES NEVID

Easy to

Moderat

e

Replacement

Section

Example of the Versatility of the Continuous Miner Operating at Chirimiri (SECL)

1 SECL JOY

An example of the versatility of the Continuous Miner operating at

Chirimiri (SECL).


November 14, 2014 7

Working Range of CMs to date in India

Mining Depth 10 m to 410 m

Pillar Centres 20 m to 47 m

Entry Heights 3.0 m to 5.8 m

Entry Widths 4.8 m to 6.5 m

GOLDER’S

APPROACH TO UNDERGROUND

MECHANISED PROJECTS

November 14, 2014 8

Design Approach

November 14, 2014 9

Use best practice and proven experience

for initial design.

Measure to confirm that expected

behaviour is taking place to confirm

design assumptions:

Behaviour of roof, ribs, floor and pillars.

Progress in stages - prove each stage

before changing.

Understand roof failure mechanisms.

Use an effective rockbolt system.

Design by measurement.

Monitor the system.

Use real data to validate computer

models.

Golder Design Process

November 14, 2014 10

Geotechnical

Assessment

Geotechnical

Report

Initial Support

System

Support Rules

Support

Implementation

Support

Verification

Routine

Monitoring

Support

Modified

Local area

unstable

Unstable

Local area stable

Stable

Support Verification

Process on

Development

Geotechnical

Assessment

Geotechnical

Report

Initial Pillar

Extraction

Method and

Support

Implementation

of Extraction Plan

Monitored

Verification

Routine

Monitoring

Modify Extraction

Method

Local area unstable

Stop Slicing move

to next Fender/Pillar

Unstable

Local area stable

continue slicing

Stable Continued

Rapid

Instability

Review Method

Verification Process

for Pillar Extraction

Method

PILLAR EXTRACTION DESIGN

METHODS



Pillar Extraction

Currently two high production mechanised coal mining methods are

used in India: Retreat longwall and room and pillar.

Pillar extraction with continuous miners in room and pillar mines has

so far been the most productive method of the two.

First applied to Anjan hill in 2002, eight more have been established

since, breaking local and national production records.

Can be applied to existing room and pillar mines by reworking

reserves left in pillars and new developments.

Pillars have been extracted using modern methods such as remote

controlled continuous miners and shuttle cars.

Substantial unworked coal deposits at shallow depth are also

potentially suitable for mechanised room and pillar mining

(Estimated at 2 – 3 Bt).

Seen by the Indian authorities as the key to increasing production.


Pillar Design

Golder uses established pillar design methods such as Salamon

and Munro (1967) for pillar sizing.

Initial pillars are given a high SoF of 2.0 to ensure stability during

pillar extraction.

The choice of pillar extraction pattern and sequence depend on site

conditions, such as overlying strata cavability.

Where the risk of difficult caving presents, yield pillar systems can

be employed.

Golder believes an adequate remnant pillar (snook), should be left

to support intersections (around 10% of initial pillar size).

Mark and Zelanko (2001) reported during pillar extraction over a six

year period, 30% of fatalities in the US were due to insufficient

snook sizing or attempts to extract the snook.


Snook Design

The smaller the snook is, the junction ‘stand-up’ time will be less.

These are snook parameters for CM5 at NCPH Old mine.


Snook Design

Relationship between snook size and caving delay in four-way

junctions for CM5 at NCPH Old Mine.


Pillar Design

To minimise ground control risks during pillar extraction:

Appropriately size pillars on development

Implement a suitable extraction sequence

Size remnant pillars to suit mine conditions

Install load cells and monitoring systems to confirm

early designs

Mechanised Pillar Extraction Methods


MODIFIED NEVID SYSTEM

5m 16

19

21

1

2

3

4

5

11

12

13

14

6

7

8

9

10

15

16

17

8

19

20

21

22

23

24

25

18

26

27

28

29 S1 S2

S3 S4

S5 S6

1 2

3 4

5 6

7

8 9

11

10

14

12

13

16

17

18

22

19

20

21

S1

S2

S3

15

3

4a 4a 4

1

5 2

3

DOUBLE SPLIT AND FENDER

1/3 SPLIT AND FENDER

47m pillar centres

(41 m pillars)

47m pillar centres

(41 m pillars)

22m pillar centres

(16 m pillars)

5

8

12

15

6m

17

16

14

13 6

7

10

9

11

5

5 8

5 12

15 1

3

26

m

2

4

SPLIT AND FENDER

15

32m pillar centres

(26 m pillars)

32 m

22 m

47 m

PILLAR PERFORMANCE

MONITORING AND MEASUREMENT


Design Monitoring Instrumentation


More accurate instruments

Comprehensive set of data on rock and support behaviour

Instruments verify pillar design by installing instruments into pillars

All instrumentation is remote reading

Also used to validate numerical models (FLAC, FLAC3D and MAP3D)

Roof and Rib Extensometers

Roof/Rib Strain Gauged Bolts

Design Monitoring Instrumentation (cont.)


Strain Gauged Rock Bolts

Fully encapsulated rockbolts develop a

load profile along their length

depending on rock properties and

stresses around the tunnel.

It is important to be able to measure

this profile.

We glue 9 pairs of resistance strain

gauges in opposed machined grooves

along the bolt.

Sonic Roof/Rib Extensometers


Installation

Anchors

Instrument

Multiple Wire Roof/Rib Remote Reading

Extensometers


Vibrating Wire Stress Cells (Pillar Loading)


Section through a vibrating

wire stress cell

Vibrating Wire

Platen

Proving Ring

CASE EXAMPLES


Pillar Loading During Pillar Extraction

CM 5 , NCPH, SECL


Monitoring Stress Change in Pillars During

Depillaring, CM5, NCPH, SECL


Seam No.3 extracted 40m above Seam No.5.

Remnant pillars left in Seam No.3 shown in GREY.




1st two pillar rows extracted

(Pillars 1 – 10)




1st two pillars extracted in 3rd row

(Pillars 11 – 12)




Pillars 13 & 14 split, and Fender A of Pillar 13 taken.

Cell 1 Extracted

(Lost)




Cell 2 Cell 3

1st three pillar rows extracted

(Pillars 1 – 15)




Cell 2 Cell 3

Pillars 16/17 Extracted in 4th Row




Cell 2 Cell 3

4th Row of Pillars Extracted

Pillar No.21/22 started to be split

21

2

2




Cell 2 Cell 3

Extraction of Fender A,

Pillar 23 Starts




Cell 2 Cell 3

Extraction of

Fender A, Pillar 23

Completed

Extraction of

Fender B, Pillar 23

Starts

Roof Fall Over

No.21 Area

Adjacent to Stress Cell

Cell No.2 Extracted

(Lost)




Cell 2 Cell 3

Non Caving Method with

Stable/Yielding Pillar Failure

VK7, SCL


Yield Pillar Partial Extraction Method

Indicating Fender Slicing Sequence

45m pillar centres

25.5m pillar core

19m max span

after slicing

(Final span will

be determined by

actual pillar size)

19m max span

after slicing

Snook width

>2 x height

min 9m

Breaker line

3 rows

7 x 2.4m bolts

@ 0.8m centres

Entries

4.6m x 6.5m

after

Bottom Coaling

No Bottom Coaling

adjacent to Barrier Pillars

To maintain FoS >2


Mining Method

Secondary Extraction by widening, bottom coaling

and partial extraction

The final remnant pillars are designed to yield in a

slow and controlled fashion


Key Elements for the Design of Yield Pillars

Remnant pillars left behind

Width/height ratio high enough to prevent

uncontrolled collapse

Span between pillars sufficiently small to prevent

most roof falls

Some small falls may occur as the pillars yield and

the roof moves

Barrier pillars to isolate panels


Key Elements of Proposed Design of Yield Pillars

40

The method relies on the pillars that are left behind

failing slowly

The mode of pillar failure is controlled by their width to

height ratio

And the stiffness of the loading system


Depth 410m

Pillar width 45m

Pillar height 2.5 to 4.6m

Entry width 3.5 to 6.5m

AVERAGE PILLAR STRESSES

0

4

8

12

16

20

24

28

32

36

40

1st

development

Road

widening

Bottom

coaling

First side Second side

Str

ess, M

Pa


Pre-

mining

Calculated Average Pillar Stresses During Mining

Depth 410m

Pillar width 45m

Pillar height 2.5 to 4.6m

Entry width 3.5 to 6.5m

PILLAR SAFETY FACTORS

0

0.25

0.5

1.0

1.25

1.5

1.74

2.0

2.25

2.5

1st

development

Road

widening

Bottom coal first side second side

Safe

ty f

acto

r

Pillar Safety factors during extraction

0.75


Calculated Pillar Safety Factors

Stresses – before secondary partial extraction

VIRGIN PILLAR

Virgin stress

=10.25Mpa

Pillar stress

=14.4Mpa (stress

concentration 1.4)

Pillar FoS > 2

w/h ratio > 9


Stresses – after 1st pillar slice taken

1st side extracted

Pillar stress

=21.5Mpa (stress

concentration 2.1)

Pillar FoS < 1


Stresses – after 2nd pillar slice taken

2nd Side extracted

Pillar stress

=31.8Mpa (stress

concentration 3.1)

Assume snook

failure

Pillar SoF < 0.5

w/h ratio > 5



Monitoring of Yield Pillar Data

from VK7, SCL

Example of Pillar Loading in Pillar No. 11


15 m

10 m

Pillar No.9


15 m

10 m

Pillar No.9



15 m

10 m

Pillar No.9

All cells lost at this point


Remote Reading Roof Exto Results, VK7,SCL

Mid Pillar 4 Way roof Exto ch.37,36

31R (77L-78L)

-

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

Ab

so

lute

An

ch

or

Dis

pla

cem

en

t (m

m)

Date

31R(77L-78L) 4-way Roof Exto Ch. 37,36

Anchor 1 1.5(m) Anchor 2 5(m) Anchor 3 10(m) Anchor 4 15(m)

Pillar 6 Completed

Exto in Waste Area

6 7 8 9 10 12 13 14 16

19 18 17 20

11

15

VK7, SCL. 31R (77L-78L) 4 Way roof Exto ch.37,36

-

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

Ab

so

lute

An

ch

or

Dis

pla

cem

en

t (m

m)

Date



Pillar 6 Completed

Exto in Waste Area

9 10 12 13 14 16

19 18 17 20

11

15


2n

d R

ow

Co

mp

lete

d

-

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

Ab

so

lute

An

ch

or

Dis

pla

cem

en

t (m

m)

Date



Pillar 6 Completed

Exto in Waste Area

13 14 16

19 18 17 20

15


2n

d R

ow

Co

mp

lete

d

3n

d R

ow

Co

mp

lete

d

-

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

Ab

so

lute

An

ch

or

Dis

pla

cem

en

t (m

m)

Date



Pillar 6 Completed

Exto in Waste Area

19 18 17 20


2n

d R

ow

Co

mp

lete

d

3n

d R

ow

Co

mp

lete

d

4th

R

ow

Co

mp

lete

d

-

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

Ab

so

lute

An

ch

or

Dis

pla

cem

en

t (m

m)

Date



Pillar 6 Completed

Exto in Waste Area

2n

d R

ow

Co

mp

lete

d

3n

d R

ow

Co

mp

lete

d

4th

R

ow

Co

mp

lete

d

140m in to Waste Area

5th

R

ow

Co

mp

lete

d


Auto-warning Telltale


Golder’s intrinsically safe Auto-warning Telltale provides a

highly visible immediate warning of excessive movement,

over and above that provided by the coloured bands on

standard telltale.

These were specifically developed for the Indian coal

market to provide real-time warning to the machine

operators of the possible onset of caving in the pillar

extraction zone during mechanised pillar mining

operations.

The extraction line is the most high risk area for fatalities

and machine burial due to the unpredictable nature of

caving during pillar extraction.

These have proved to be highly effective and have now

been adopted as the standard means of monitoring in

mechanised pillar extraction panels in India.


Example of Auto-Warning Response

During Pillar Extraction in CMP 6, SECL

Visibility of Auto-Warning Telltale – in Operation

CMP1 Panel, -26L from 29R

AutoWarning.wmv

v

v

2

7

8

1

54N

53N

52N

11E 12E 13E 14E 15E 16E

10 9 18/4/12 5:20 21/4/12 18:30

4

1/5/12 18:00

3 5

6

9/5/12 13:00

18/5/12 7:00

19/5/12 23:30

Extraction Sequence with Caving and AWTT Triggering

Times during the Extraction of Pillars 1 to 10


The application of mechanised room and pillar mining systems in

India for the development and the re-establishment of old

workings prior to subsequent pillar extraction has proved to be

very successful.

Pillar extraction is important to India, as vast reserves of coal still

exist underground in old mining districts as pillars.

The risk of ground control failure during pillar extraction is

relatively high, especially where overlying strata conditions are

high such as found at some India sites.

This risk has been reduced with the help of Golder, by adopting

appropriate pillar design and support, extraction sequences.

Summary


Remote monitoring of selected pillars during extraction with

instruments provides confirmation of behaviour and verifies

designs.

Safety procedures undertaken during pillar extraction now include

the use of Golder’s AWTT, which flash when dangerous roof

movement is detected. This is significant to operator safety during

pillar extraction. However, experiences shows their relative

effectiveness can be site specific and therefore should not be

used in isolation.

The potential for the application of mechanised room and pillar

mining with CMs in India is significant having the potential to

achieve world class productivity while maintaining safety.

Summary cont.

AusRock2014 - 5/6th November

5

8

12

15

6m

17

16

14

13 6

7

10

9

11

5

5

8

5 12

15 1

3

26

m

2

4

SPLIT AND FENDER

15

32m pillar centres

(26 m pillars)

32 m

Thank you for your attention

ausrock2014 - 5/6th november coalmine pillar design and ... · 6 ecl sarpi joy r -vii 4.0 5.5 120...

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