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

THE GROSVENOR EXPERIENCE January 2016 INTERNAL

• Background & Expected Conditions • Our Experiences • Major Review • Future Works 2 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 3 INTERNAL

GROSVENOR Geology and Geotechnical Environment 166 166 Seam Roof 1 0.7m Ply 1 Band 2 0.8m Ply 2 Band 168 168 3 2.1m 5.2m 4A 4B 5T 170 170 Tonstein Band 5B 1.2m Seam Floor 4 INTERNAL

• Background & Expected Conditions • Our Experiences • Major Review • Future Works 5 INTERNAL

OUR EXPERIENCES I nexistence of a Coal Roof “Beam” • 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 6 Density plots of GRO and MNC outside split zone, highlighting difference of transitional coal roof INTERNAL

OUR EXPERIENCES Low Strength Roof Environment • 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 7 INTERNAL

DEVELOPMENT EXPERIENCE Max Displacement per CT - TG101 140 400 Split Zone Begins 350 120 300 100 Max Displacement (mm) 250 80 Floor Cut to Increase Coal Beam DoC (m) 200 90° Break – travel to belt rd 60 150 New Support Rules 40 Truss Support 100 Truss Support Fenoflex Trial MW10 Trial MW10 Trial MW10’s 20 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Cut Through Reasonably benign conditions 8 < 220m DOC. No major Issues INTERNAL

150 400 100 200 TG101 8 CT 50 0 0 90° Breakaway – Stress Orientation 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 9 INTERNAL

150 400 100 200 TG101 10 CT 50 0 0 Fenoflex – Arrest Roof Displacement 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 10 INTERNAL

150 400 100 200 TG101 13 CT 50 0 0 First CT Driven in Split Zone 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 11 INTERNAL

150 400 100 200 TG101 14 CT 50 0 0 Trusses Installed – Arrest Roof Displacement 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 12 INTERNAL

150 400 100 200 TG101 15 CT 50 0 0 First Trial MW10 Megabolt – Minimise Displacement 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 Minimal fracturing/shearing 13 INTERNAL

150 400 100 200 TG101 16 CT 50 0 0 Cut on Floor - Increase Coal Beam 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 14 INTERNAL

150 400 100 200 TG101 18 CT 50 0 0 Second Trial MW10 Megabolt – Minimise Displacement 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 Floor heave identified in TG101 18 C/T – floor simply ‘popped up’ during inspection 15 INTERNAL

150 400 100 200 TG101 20 CT 50 0 0 Cut into floor - Increase Coal Beam 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 16 INTERNAL

150 400 100 200 TG101 22 CT 50 0 0 Revised Support Rules 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 • 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 +17m +17m +34m 17 INTERNAL

• Background & Expected Conditions • Our Experiences • Major Review • Future Works 18 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 – I n 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) 19 INTERNAL TG101 UCS Plot

MAJOR REVIEW Key Changes to MMSR and TARP Triggers • 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) LOCATION SUPPORT DENISTY TELLTALE TRIGGER 2 x 8.2m long cable per 1m <100mm Gateroad Cut Throughs 100mm – 130mm and Intersections As above + 1 x C/L 8.2m Megabolt per 1m 130mm – 150mm As above + 10m Trusses every 2m 2 x 8.2m Megabolt per 4m <40mm Gateroads Headings 40mm – 60mm 2 x 8.2m Megabolt per 2m 60mm – 80mm As above + C/L 8.2m Megabolt per 2m 20 INTERNAL

• Background & Expected Conditions • Our Experiences • Major Review • Future Works 21 INTERNAL

WHERE ARE WE GOING? Trials and Future Works • 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 22 INTERNAL

WHERE ARE WE GOING? Future Challenges Expected • 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? 23 INTERNAL

THANK YOU

APPENDICIES 25 INTERNAL