THE GROSVENOR EXPERIENCE January 2016 INTERNAL Background & - - PowerPoint PPT Presentation

THE GROSVENOR EXPERIENCE

January 2016

INTERNAL

2 INTERNAL

• Background & Expected Conditions
• Our Experiences
• Major Review
• Future Works

3 INTERNAL

GROSVENOR

Mine Specifications

• 7 Mtpa Longwall coal operation
• Situated between existing Moranbah North mine & Moranbah South Project
• Goonyella Middle (GM) Seam in Moranbah Coal Measures
• Development achieved 26 km in 2015 with:

– 3 x ED25 – 2 x 12CM12

• Longwall mining to commence May 2016
• Designed on the back of mining experiences with

similar environments

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GROSVENOR

Geology and Geotechnical Environment

166 168 170

1 2 3 4A 4B 5T 5B

166 168 170

5.2m 1.2m 2.1m 0.8m 0.7m

Tonstein Band Ply 2 Band Ply 1 Band Seam Roof Seam Floor

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• Background & Expected Conditions
• Our Experiences
• Major Review
• Future Works

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OUR EXPERIENCES

• Not a typical coal beam as seen in Moranbah North (MNC)
• Grosvenor Ply 1 classed as transitional from coal to the overlying carbonaceous mudstone above
• Geotechnically low strength coal roof – is transitional by nature containing multiple bands

Density plots of GRO and MNC outside split zone, highlighting difference of transitional coal roof

Inexistence of a Coal Roof “Beam”

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OUR EXPERIENCES

• Roof

– Immediate roof strength impacted by seam split – Split zone interburden low strength (<10 MPa), thinly bedded, carbonaceous and/or tuffaceous claystone unit – Highly carbonaceous mudstones with sheared & polished bedding planes continues above/below ply 1

Low Strength Roof Environment

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DoC (m) Max Displacement (mm) Cut Through

DEVELOPMENT EXPERIENCE

Max Displacement per CT - TG101

90° Break – travel to belt rd Fenoflex Trial Truss Support Reasonably benign conditions < 220m DOC. No major Issues

Split Zone Begins

MW10 Trial Floor Cut to Increase Coal Beam MW10 Trial MW10’s Truss Support New Support Rules

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TG101 8 CT

• DoC 220m
• Driven 90° - Prove driving into principal stress improves productivity (unsuccessful)

– Cleat direction within 15° of roadway (triggered TARP to elevate support) – Roof Displacement thought to be due to Cut Through (CT) orientation

• Support: 6 x 1.8m bolt per m and 2 x 6.2m Megabolt (MW9) every 2m
• 50mm trigger: 1 x 8.2m Centreline (C/L) Megabolt (MW9) every 2m
• Maximum Total Displacement (MTD) 70mm

90° Breakaway – Stress Orientation

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TG101 10 CT

• DoC 245m
• Changed primary support - 8 bolt pattern (inbye 9 CT)
• Megabolts in belt road intersection grouted prior to breakoff (previously grouting TARP driven)
• TARP revision for CT’s:

– 30mm Trigger to grout Megabolt (MW9) – 50mm Trigger install 1 x 8.2m C/L Megabolt (MW9) – All CT’s driven with 2 x 8.2m Megabolt (MW9) per m at minimum

• Displacement > 70mm resulted in Fenoflex to be injected belt road side of CT (unsuccessful)
• MTD 96mm

Fenoflex – Arrest Roof Displacement

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TG101 13 CT

• DoC 280m
• Primary support 8 bolt pattern with 2 x 8.2m Megabolt (MW9) per m
• Megabolts grouted at 30mm, completed CT, tell-tales stable at 40mm
• During 14CT driveage, roof reactivated, installed C/L Megabolts (MW9)
• After second surge CT stabilised
• MTD 72mm

First CT Driven in Split Zone

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TG101 14 CT

• DoC 290m
• High rate of displacement (40mm in 24 hours) – no sign of arresting
• At 50mm displacement installed 8.2m C/L Megabolts (MW9)
• To pre-empt 80mm displacement Trusses installed at 2m spacing (successful)
• MTD 84mm

Trusses Installed – Arrest Roof Displacement

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TG101 15 CT

• DoC 300m
• Trial of higher capacity Megabolt (69t MW10 compared to 60t MW9)
• MW10

– 2 x1000mm resins – Unbonded section of ~3.5m – 2m grout tubes installed

• Least amount of movement of a CT in the split zone (inconclusive due to sandstone in Megabolt

horizon)

• MTD 18mm

First Trial MW10 Megabolt – Minimise Displacement

Minimal fracturing/shearing

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TG101 16 CT

• DoC 310m
• Cut on floor to increase coal beam thickness by 300mm
• Significant bagging & C/L cracking observed – comparable to outbye C/T’s
• At 50mm movement, 1 week after driveage installed C/L Megabolt (MW9)
• Trial of full column grouting of Megabolts (MW9) every window – no sign of arresting displacement
• Observed shearing at 2 - 4m roof horizon
• Cut on floor with MW9s (unsuccessful)
• MTD 71mm

Cut on Floor - Increase Coal Beam

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TG101 18 CT

• DoC 320m
• Continued to cut on floor with retrial MW10’s
• First sign of floor heave

– Generally in isolated areas (10-15m in length, CT’s more susceptible) – Difficult to quantify – estimated 300mm – Developed site specific floor heave potential index

• MTD 28mm

Second Trial MW10 Megabolt – Minimise Displacement

Floor heave identified in TG101 18 C/T – floor simply ‘popped up’ during inspection

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TG101 20 CT

• DoC 350m
• Cut 400mm into floor to increase coal beam thickness by 700mm (C 19-20 & 20 CT) (unsuccessful)
• High rate of displacement (>30mm in 12 hours) – no sign of arresting
• Excessive rib spalls >0.5m due to Tonstein higher in ribs
• Slippery stone floor, blocky when broken
• At 115mm displacement installed Trusses
• MTD 131mm

Cut into floor - Increase Coal Beam

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TG101 22 CT

• DoC 360m
• First CT driven with revised support rules and TARPs – fundamental changes
• MW10s grouted every window
• To pre-empt 100mm displacement C/L Megabolts (MW10) installed at 90mm (2m spacing)
• High displacement triggers allowed completion of CT before C/L’s

– C/L support taken offline, no delays (successful)

• MTD 122mm

Revised Support Rules

+34m +17m +17m

18 INTERNAL

• Background & Expected Conditions
• Our Experiences
• Major Review
• Future Works

19 INTERNAL

MAJOR REVIEW

• Grosvenor geotechnically characterised as a low strength roof environment (CMRR ranges 30-35)
• Conditions have been managed successfully to date

– Current market dictates need to drive efficiency into strata management

• Grosvenor’s low strength roof:

– Accept the roof displacement (plastic deformation) process and design accordingly

• Major review undertaken by external consultants about key strategies to follow

– In conjunction with numerous trials have resulted in our current support rules and TARP’s – Moved towards higher capacity Megabolt support with un-bonded section (MW10)

TG101 UCS Plot

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MAJOR REVIEW

• No coal beam thickness trigger – Grosvenor does not have a coal beam
• Strategy based around moving towards a suspension type model
• Increased telltale triggers
• Relaxed centreline crack trigger - > 50mm cracking in addition to other deformation signs results in

moving up a support level

• Post groutable un-bonded Megabolt (MW10) with routine grouting every 24 hours, unless specified by

displacement trigger (> 50mm in 12 hours)

Key Changes to MMSR and TARP Triggers

LOCATION SUPPORT DENISTY TELLTALE TRIGGER Gateroad Cut Throughs and Intersections 2 x 8.2m long cable per 1m <100mm As above + 1 x C/L 8.2m Megabolt per 1m 100mm – 130mm As above + 10m Trusses every 2m 130mm – 150mm Gateroads Headings 2 x 8.2m Megabolt per 4m <40mm 2 x 8.2m Megabolt per 2m 40mm – 60mm As above + C/L 8.2m Megabolt per 2m 60mm – 80mm

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• Background & Expected Conditions
• Our Experiences
• Major Review
• Future Works

22 INTERNAL

WHERE ARE WE GOING?

• Number of key areas we are investigating

– Bolt length review: Would moving to a 2.1m bolt make a difference? – High capacity point anchored bolts: Could this be the answer to eventually reducing Megabolt density? – Analytical rating specific to Grosvenor that can be linked to required support density – Further development of ground deformation curves for weak roof environment: How much movement will happen regardless of support density? – New roof mesh trial – very high MPa and lightweight steel

• Act as a strap across the roadway to combat

centreline sag

• Address tearing issue in heavily deformed cut

throughs

Trials and Future Works

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WHERE ARE WE GOING?

• Depth of cover increasing to deepest in QLD (currently mining MG102 to 480m)
• Bottom rib bolt issues – spalling lower rib
• High gas content inbye LW102
• LW startup early May – mine optimised for LW retreat, however what conditions will we encounter?

Future Challenges Expected

THANK YOU

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APPENDICIES

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TG101 LITHOLOGY SUMMARY

14ct 9ct 10ct 11ct 8ct 12ct 13ct 16ct 17ct 19ct 16ct to 21ct based on cutting on the floor profile 21ct 25ct-26ct 29ct

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GROSVENOR STRESS MAP

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OUR EXPERIENCES

Telltale Movement CT vs Hdgs

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DoC (m) Max Displacement (mm) Heading

Max Displacement per Heading - TG101

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20 40 60 80 100 120 140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 DoC (m) Max Displacement (mm) Cut Through

Max Displacement per CT - TG101

29 INTERNAL

CENTRELINE CRACK INVESTIGATION

Centreline cracking and Roof Bagging

• Investigation into vertical extents of

significant centreline crack – had 42mm holes drilled inside the cracks and inspected with borescope camera

• Most notable observation: significant

cracking >50mm extended ~200-300mm into the roof and appeared to stop out at a bedding plane

LOCATION HEIGHT OF FRACTURING OBSERVED MG102 6CT 0.6m MG101 7CT 0.6m MG101 11CT 1.2m TG101 8CT 0.5m TG101 14CT 0.5m TG101 17CT 0.7m

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SEAM ROOF IN SPLIT ZONE

• When the interburden between the ply 1 and ply 2 is greater than 200mm the GM seam roof is taken from the

top of the ply 2 band

• Shows immediate 3m of roof above Ply 2 (cut horizon) has Sonic Derived UCS ~10 MPa.

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GROSVENOR - ACTUAL SEAM SECTION

• Penny Band almost invisible.
• Clearly marked Ply2-Ply3 Band (Marker band for

development roof).

• Tonstein band clearly identifiable
• In ideal situation, Coal roof beam about 1.3m.