Remote Reading Tell-tale Systems in Underground Mines

Chris Wagner

Strata Engineering (Australia) Pty Ltd

Outline

• What is the Remote Reading Tell-tale System?

• The original “Tell-tale”

• The Remote Reading Tell-tale (RRTT)

• The RRTT System

• Benefits of the system

• Limitations of the system

• Where has it been used?

• Where to from here

Strata Engineering (Australia) Pty Ltd

What is the Remote Reading Tell-tale (RRTT) System?

• Based on the original dual height mechanical Tell-tale developed in in the UK in the 1980’s

• The RRTT system is an approved intrinsically safe (IS) electronic Tell-tale system which allows real time measurement of roof displacement to a surface computer

• The RRTT system was developed by Golder RMT UK in the late 1990’s following the success of the mechanical Tell-tale

Strata Engineering (Australia) Pty Ltd

The Original “Tell-tale”• Purely visual indicator

• Uses a traffic light system, Green, Yellow and Red

• Has mm display for more accuracy

• Two indicators connected to stainless steel wires with spring anchors

• Indicates displacement above and within the roof bolted horizon

The Remote Reading Tell-tale (RRTT)• Looks the same as the standard

mechanical Tell-tale

• Easily installed and in a similar manner to the original

• Built within the instrument is a coil and ferrite core for each anchor

• As the roof moves downwards, the coil moves over the ferrite and induces an electric charge which varies the inductance.

• The variation in inductance is then converted to displacement

• Accurate to 0.1 of a mm

"A" Indicator

"B" Indicator

Stabiliser

Coil "B"

Coil "A"

Spring Anchor

Ferrite Core "A"

ElectronicsDrip tray

Water seals

Ferrite Core “B"

The Remote Reading Tell-tale System- Basic Set Up

Daisy chain of Tell-tales installed in roadways and cut-throughs

Computer, barrier & comms.

Underground Interrogation Unit(powered by an IS 12v power supply)

From Surface to Seam

• The mine can chose to run a twisted pair wire (telephone line) from the surface to the proposed location of the Interrogation Units or alternatively, connect the system to an existing underground phone line.

• The 12v IS power supply is set–up as required for each Interrogation Unit

• The surface barrier unit, communications and PC (including the supplied software) are then set-up prior to going underground

• Once the above is completed and tested the underground installation commences

Basic Connection of the Interrogation Unit and Tell-tales

2. Twin-core wire from the surface is then connected to the Interrogation Unit

3. Finally, a simple twist and crimp connection is made to the first Tell-tale or connecting cable

1. Interrogation Unit is installed on the rib and connected to the 12v IS power supply by the mine electrician

Software Set-up• Once underground connection has been completed, all existing Tell-

tales are identified and labelled in the software

• Trigger levels are set – standard levels are typically as per those shown on the visual indicators:- Green (0-25mm)- Yellow (25-50mm)- Red (50-75mm)Note: these levels can be changed in the set-up of the software if different triggers are warranted

• Following the initial set-up, each time a new Tell-tale is added to the daisy chain, the Interrogation Unit identifies it and flags it in the software ready to be labeled

Benefits of the RRTT System• REAL-TIME Monitoring (100 Tell-tales can be read in under 20 minutes)

• Less demand on man-power

• The Remote Reading Tell-tale is contact-less, minimising the potential for mechanical failure

• Requires very low power

• Internal electrics are fully sealed and are therefore not sensitive to moisture

• Ability to set high reading frequencies and specific trigger levels

• Access to gassy and sealed off areas

• Allows on-going monitoring of remote or high areas

• Is easily integrated with existing database software

• Cost

Limitations of the RRTT System

• A maximum of 100 Tell-tales and / or 2km of connecting wire can be monitored on any one underground Interrogation Unit however, if less than 100 Tell-tales are installed, the length of connecting cable can be increased beyond the 2km typical maximum.

• Currently the system can only monitor 4 x underground interrogation units per PC and therefore a maximum of 400 x Tell-tales per surface PC

Some Site Examples

1. West Mine - Germany• Use: monitoring maingate conditions during the retreat of LW 183

• Set up in single entry maingate (limited personnel access)

• Roadway was kept open during longwall retreat (using standing support) to allow roof monitoring inbye of the face

• 67 Tell-tales installed along the daisy chain

• Approx. 1.3km of roadway monitored

• Depth of Cover of >1000m

• Twisted pair line had to be run ~12km into the mine

Output from West Mine in Germany- During LW Retreat

West Mine Germany – Individual Tell-tale

Station 52, 862m

0

5

10

15

20

25

30

Date

Dis

plac

emen

t (m

m)

0

2

4

6

8

10

12

14

16

18

20

Face

Pos

ition

(m)

Face Distance 52 AA 52 BB

Acceleration in displacement in the bolted

horizon when LW was <4m from Tell-tale

LW Retreat - West Mine Germany

19 December 2001. Face Position 882m.

0

10

20

30

40

50

60

70

80

-40

-20020406080100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

700

Distance from Face Line (m)

Roo

f Dis

plac

emen

t (m

m)

A telltale (mm) Total Movement (mm)

Summary of all Tell-tales as LW approaches

Surge in displacement following the passing of

the longwall

Early roof displacement around 300m outbye of the

longwall

2. Daw Mill – United Kingdom• Use: monitoring sealed longwall

• Why? For access to equipment behind stoppings at a later date.

• 13 Tell-tales installed along daisy chain in a single entry maingate

• Standard Trigger Levels set:

- Green 0-25mm

- Yellow 25-50mm

- Red 50-75mm

Daw Mill Colliery – UK- Location Plan

Maingate

31’sStoppings

301’s

13 x Tell-tales

LW Stop Position

Output from Daw Mill Colliery, UK

Trigger levels exceeded – Yellow Trigger (25-50mm)

on the A Anchor = bolted horizon

Daw Mill Colliery, UK

RRTT Daw Mill Colliery, 301's MG

0

5

10

15

20

25

30

35

40

45

50

27-Ju

l-05

16-A

ug-05

05-S

ep-05

25-S

ep-05

15-O

ct-05

04-N

ov-05

24-N

ov-05

14-D

ec-05

03-Ja

n-06

23-Ja

n-06

12-Feb

-06

04-M

ar-06

24-M

ar-06

13-A

pr-06

03-M

ay-06

Date

Roo

f Dis

plac

emen

t (m

m)

365m TT13 A Reading 365m TT13 Total

360m TT12 A Reading 360m TT12 Total

340m TT11 A Reading 340m TT11 Total

320m TT10 A Reading 320m TT10 Total

Location of trigger level events

3. Marathon Petroleum Gas Cavern – West Virginia US

• Use: monitoring roof movement in gas cavern

• 64 Tell-tales running a 10 minute reading interval

• Due to shape of cavern, complex connection topology required

• Several 3 and 4-way connections had to be made

• Interrogation unit set up on surface rather than underground

• Approx. 1.5km of connecting cable in system

100ft

Marathon Petroleum Gas Storage Cavern- West Virginia USA

Movement Recorded on EN +100 (Channel 31)

Cavern and Connection Layout

Marathon Petroleum Gas Storage Cavern- Movement on EN +100 in Days

0

2

4

6

8

10

12

14

16

18

20

10/08/2009 11/08/2009 12/08/2009 13/08/2009 14/08/2009

Roof

dis

plac

emen

t (m

m)

Date

Bolted height (A) Total Movement to 5m (A+B)

Indicates majority of movement occurring in the

bolted horizon

Marathon Petroleum Gas Storage Cavern- Detailed Section of Movement (hours)

0

2

4

6

8

10

12

14

16

18

20

Roof

dis

plac

emen

t (m

m)

Time

Bolted Height (A) Total Movement to 5m (A+B)

Ability to pin-point when the movement started (hours)

4. Experimental Mine - Indonesia• Use: monitoring roof movement during roadway development of run-

outs and retreat pocketing

• 20 x roof extensometers (4 x anchor as opposed to dual height Tell-tale)

• 21 x rib extensometers

• 8 x stress cells

• Use was made of the Portable Readout Unit as opposed to the underground interrogation unit and surface PC

Experimental Mine - Indonesia• All monitoring sites were wired back to an individual location

underground where they were able to be read utilising the hand-held Portable Readout Unit

4 x Anchor Remote Reading

Extensometer

Hand-held Portable

Readout Unit

Indonesia Experimental Mine - Layout

Roof Exto Telltales shown.....Rib Exto Telltales shown.......Stress cells shown.................

Roof Extensometer No. 3

Retreat development of

run outs and pockets

Results from Roof Exto 3 – During Development of Run-outs and Pocketing

Increase in roof displacement measured as pocketing retreats closer to Exto 3

Limited movement measured above the bolted horizon

5. Angus Place Colliery – NSW Australia• Use: monitoring roof displacement during the driveage of first pass and

subsequent widening in LW 970’s installation road

• 30 x dual height Tell-tales installed in both the installation and bleeder roadways

• Installation road located approx. 9km into the mine

• Underground interrogation unit was installed in the crib room approx. 200m outbye of the installation road

• During initial site visit, full surface to seam set-up completed and 12 x Tell-tales were installed

• Remaining Tell-tales were installed either off the miner as development advanced or outbye by the mine site Geologist

• RRTT system has been integrated into the mine’s existing access exto database

Angus Place Colliery – Layout

970 Panel

LW 9

70 In

stal

latio

n R

oad

Green Tell-tales installed outbye of face during initial

site visit and set-up

Majority of red Tell-tales installed at the face off the

miner

LW 970 Installation Road

– 38m from MG Intersection

Initial surge in displacement as miner developed towards TG

end of roadway

Overall very limited amount of displacement (ie, <7mm)

Displacement is confined to the bolted horizon (ie, A anchor)

LW 970 Installation Road– 90m from MG Intersection – Mid-face Int

Note the limited surge in displacement recorded during

the formation of the intersectionInitial surge in displacement as

miner developed towards TG end of roadway

Overall very limited amount of displacement (ie, <8mm)

LW 970 Installation Road– 200m from MG Intersection

Minor ongoing movement following roadway widening measured in the bolted horizon only – overall limited

(ie, <10mm) displacementSurge as a result of roadway

widening

Where To Next?

Mine Plan and Trigger Level Integration

(i) Colour immediately shows Engineer trigger level exceeded and (ii)

displacement amount also plotted

- SMS and email alerts for Tell-tales which have exceeded the prescribed trigger level

- Software upgrades including;

(i) Network server installation with the ability for multiple users to review the data simultaneously and remotely

(ii) Improved system diagnostics