GEOTECHNICAL ASPECTS OF BORD AND PILLAR MINING AT ENSHAM BBUGS - - PowerPoint PPT Presentation

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GEOTECHNICAL ASPECTS OF BORD AND PILLAR MINING AT ENSHAM BBUGS - - PowerPoint PPT Presentation

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GEOTECHNICAL ASPECTS OF BORD AND PILLAR MINING AT ENSHAM BBUGS Presentation 29 th May 2014 GORDON GEOTECHNIQUES OUTLINE OF PRESENTATION MINE LAYOUT ENGINEERING GEOLOGY MINING METHOD MINING HORIZON PRODUCTION

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SLIDE 1

GORDON GEOTECHNIQUES

GEOTECHNICAL ASPECTS OF BORD AND PILLAR MINING AT ENSHAM

BBUGS Presentation – 29th May 2014

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SLIDE 2

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

OUTLINE OF PRESENTATION

  • MINE LAYOUT
  • ENGINEERING GEOLOGY
  • MINING METHOD
  • MINING HORIZON
  • PRODUCTION RESULTS
  • GROUND SUPPORT
  • FAULTING
  • ROOF SPLIT
  • STRESS CONDITIONS
  • GROUNDWATER
  • PILLAR DESIGN
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SLIDE 3

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

MINE LAYOUT

  • >2.5 Mt mined so far
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SLIDE 4

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

STRATIGRAPHY

  • Extract the coalesced Aries-Castor Seam (A2C) in the Rangals
  • Seams split to north and south.
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SLIDE 5

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

SEAM THICKNESS AND SPLITS

A211 PLY ROOF SPLIT CASTOR SPLIT

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SLIDE 6

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

DEPTH OF COVER

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SLIDE 7

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

MINING METHOD

7 HEADINGS 9 HEADINGS

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SLIDE 8

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

DEVELOPMENT CONDITIONS

Roadways 6.5 m wide and 3.5 m high.

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SLIDE 9

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

BOTTOMS EXTRACTION

Typically 1-1.4 m of bottoms.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

POCKETING

  • For

a 5 m extraction height, 1500-2000 tonnes in each pocket

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SLIDE 11

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF LITHOLOGY AND STRENGTH

  • Immediate 2 m of stone roof - 20-40 MPa.
  • 2-6 m of stone roof – 30-40 MPa.
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SLIDE 12

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

MINING HORIZON

  • Initially mined to stone roof but slabbed in

places.

  • Now mine to penny band 0.9-1.1 m from roof

leaving the higher ash coal in the roof

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SLIDE 13

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

MINING CONDITIONS

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SLIDE 14

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PRODUCTION HIGHLIGHTS (FOR TWO UNITS)

  • Best Shift
  • 4,777 tonnes
  • Best Day
  • 7,578 tonnes
  • Best Week -

40,140 tonnes

  • Best Month -

145,649 tonnes

  • 140,000 tonnes/month equates to 80 km/year of a typical 5 m x

3 m gateroad drivage

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SLIDE 15

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

90 DAY AVERAGE PRODUCTION

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Tonnes per Day Mined

90 Day Average 800kt Per Unit Rate

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SLIDE 16

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

GROUND SUPPORT

  • 4 x 1.5 m roof bolts every 1.5 m in a 6.5 m wide roadway.
  • 1 x 1.5 m rib bolt mid pillar and 2 x 1.5 m rib bolts on corners.
  • In coal roof, only mesh services roadway and when triggered

by the TARP.

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SLIDE 17

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF BOLTING ISSUES IN FAULTED AND ROOF SPLIT AREAS

  • Centre cracking in coal roof beam.
  • Gloving on roof bolts.
  • Fracturing at top of bolted horizon.
  • Poor encapsulation.

200 400 600 800 1000 1200 2 4 6 8 10 12 14 16 18 20 22

LENGTH OF NON‐ENCAPSULATION (mm) SAMPLE NUMBER

SW Mains 49‐50CT NW Mains 1‐4CT Average SW MAINS = 220 mm Average NW MAINS = 575 mm

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

POTENTIAL DEFICIENCIES IN BOLTING SYSTEMS

(ACARP Project C21023 – Mine Advice)

Gloving and unmixed resin at top of the bolt

Lower ratio

Higher ratio

Resin back pressure

Different mastic/catalyst ratios

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SLIDE 19

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

BENEFITS

  • Guaranteed tensioning of the roof and rib bolts.
  • Reduction/elimination of gloving and unmixing of the resin at the back
  • f the hole.
  • Reduction in roof bolt length for the same effective support.
  • Reduces the variety of plates and bolts used in a panel - 200 mm plate

replacing star plates and dragonfly plates.

  • Reduced manual handling.
  • Reduced pressure at back of hole due to shorter resin.

NEW SYSTEM

  • 500 mm, 2:1 fast set resins in 28 mm holes using 200 mm square

plates.

  • With 1.5 m bolts still get 70-75% encapsulation.
  • Also looking at bolts with “neutral” deformations so that no resin

pumping action is generated further reducing back pressure.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

HISTORY OF GROUND SUPPORT

DATE SUPPORT INSTALLED October 2011 1.8 m roof and rib bolts with 1000 mm, 4:1 water based resins and roof mesh. May 2012 Dropped off mesh in stone roof roadways in NW1 Panel. January 2013 Leave coal roof in SW Mains and SE2 Panels. March 2013 Dropped off mesh in some coal roof roadways in SW Mains August 2013 In seam split area (interburden >0.8m), initially additional 2 x 4 m cables every intersection reduced to 4 x 2.4 m bolts. November 2013 Reduce rib bolt pattern from 2 bolts/1.5 m to 1 bolt/1.5 m in the mid pillar region. December 2013 Reduce rib bolt length to 1.2 m. February 2014 Introduced 500 mm water based 2:1 fast set resins and increased to 28 mm diameter bolt hole. Late March 2014 1.5 m roof and rib bolts.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

FAULTING

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

FAULT CONDITIONS

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

DETERIORATION OF COAL ROOF NEAR FAULTS

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SLIDE 24

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF SPLIT

1.8m BOLTS 1.5m BOLTS

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF SPLIT

  • Need to anchor securely into the

stone roof above the A211 coal ply.

  • Stone between split and main seam

is weak.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF MONITORING IN SEAM SPLIT AREA

2 4 6 8 10 12 14 16 18 20 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

TOTAL MOVEMENT (mm) THICKNESS OF SEAM SPLIT INTERBURDEN (m)

B2 SE3 EXTENSION ‐ LARGE INTERSECTION NEAR A FAULT

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SLIDE 27

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

ROOF MONITORING

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SLIDE 28

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

RIB CONDITIONS – ORIENTATION

  • 103

Panel reoriented to maximise recovery between faults

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SLIDE 29

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

HORIZONTAL STRESS

  • NNE trending orientation
  • Major Horizontal:Vertical – 1.3-2
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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

GROUNDWATER

  • One of the major factors affecting productivity.
  • Stubs on down dip side of panel.
  • Easier to mine down dip as can manage water at the face.
  • Mining uphill water sits outbye of face and harder to

manage.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PILLAR DESIGN - FACTOR OF SAFETY

  • FOS >1.6 below the flood plain.
  • FOS>2.11 below the Nogoa and Anabranch.
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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PILLAR DESIGN – WIDTH TO HEIGHT

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PILLAR SIZES

Have tried different sizes including:

  • 14.5 m x 14.5 m (solid)
  • 14.5 m x 17.5 m (solid)
  • 16 m x 17.5 m (solid)
  • 17.5 m x 17.5 m (solid)
  • 17.5 m x 21.5 m (solid)

Preferred size that suits the place change method with 14 m plunges is 16 m x 21.5 m (solid) – 45.4% extraction ratio.

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GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PILLAR DESIGN AND FAULTS

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SLIDE 35

GORDON GEOTECHNIQUES

BBUGS Presentation – 29th May 2014

PILLAR DESIGN AND SOFT FLOOR

  • Very soft floor layers (<1 MPa) can

lead to panel collapse.

  • No signs of floor heave at Ensham.
  • Immediate floor strength 10-30 MPa

COAL FLOOR