Design of Remedial Support in Belt Drift, Moranbah...

Design of Remedial Support in Belt Drift,

Moranbah North Mine

Ismet Canbulat

Outline

Summary of rib fall at Moranbah North MineGeology in and around the driftsLessons learntRemedial work carried out

Immediate Long-term

Design of long term remedial support designSystems implemented following the rib fallAcknowledgementsMegabolt specs

Rib Fall

On Sunday 18/01/09, a section of the rib, located within a tuff/claystone unit, in the conveyor drift failed at Moranbah North Mine.

Material that had been previously contained by the strata support (roof bolts and shotcrete) slumped and came to rest against the drift conveyor after approximately 13 years of development.

Stop the production and development for 7 days

Rib Fall

Dimensions of the Fall

FLOOR

ROOF BeltStructure

Total Weight = 334.6 tonnesSupport Design SF = 2.4

Original Support Design

Geology

Steel arches installed

Geology

Lessons Learnt

When the rock mass is weak, use grout not resin to fully encapsulate

Monitor encapsulation length

Use corrosion protective cables/bolts in prone area

Do not rely only on shotcrete visual monitoring only

Respond the warnings in a timely manner

Immediate Remedial Support Installed

Risk Assessment and Investigation Concluded

The adequacy of the support in the drifts should be evaluated

The monitoring systems we use should be evaluated

The corrosion impact on the integrity on the previously installed areas should evaluated

Our response to defect reports should be improved

All critical areas should routinely be reviewed by the geotechnical engineers

Develop TARPs for the drifts

Remedial Support Design

Overburden(claystone/tuff/soil)

Floor(weathered basalt)

Drift

Roof bolts(not installed at this stage)

Floor concrete

22m

18m

46.7m

Overburden(claystone/tuff/soil)

Floor(weathered basalt)

Drift

Roof bolts(not installed at this stage)

Floor concrete

22m

18m

46.7m


6.700 m

2.900 m

0.300 m

5.050 m

2.150 m


Step 1:• No mining – virgin

conditions

Step 2:• Tunnel is excavated

Step 3:• 50 mm thick shotcrete

is applied

Step 4:• Bolts are installed and • Another 50 mm thick

layer of shotcrete is applied

Step 5:• Floor is concreted• Remedial support is

installed


TotalDisplacementm

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

-20

24

68

-8 -6 -4 -2 0 2 4 6 8 10 12 14

Total displacement

Shotcrete failure


MaximumShear Strain

0.00e+000

1.00e-003

2.00e-003

3.00e-003

4.00e-003

5.00e-003

6.00e-003

7.00e-003

8.00e-003

9.00e-003

1.00e-002

1.10e-002

1.20e-002

-20

24

68

-8 -6 -4 -2 0 2 4 6 8 10 12 14

Maximum shear strain

Possible failure planes following the failure of shotcrete


Bolt numbers

1

2

3

4

5

6 7

8

9

10

11

12

13


Axial load on selected bolts

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.5 1 1.5 2 2.5 3 3.5

Distance [m]

Axi

al F

orce

[MN

]

Bolt 1 Stage 5 Bolt 4 Stage 5 Bolt 13 Stage 5

Numerical Modelling Strategy

Back analysis of the fall

2 cable pattern

4 cable pattern

5 cable pattern

6 cable pattern

7 cable pattern

Increased thickness of shotcrete

Various other combinations of shotcrete

Remedial Support Design1.

4m

2.1m

1.0m

Floor

Roof

1.0m

Defect Reporting System

An established (quantitative) easy to use reporting system.

Eliminate human factor from making critical decisions with regard to response time.

Simple, accurate decision making process with regard to prioritising the defect maintenance.

Accurate data recording system.

Simple, monthly defect reporting system.

Defect Reporting System

Input

Exposure

Risk &Response

Number of People in this section (both shifts)

Time of stay of people (minute)

Number of shifts Width Length

Risk to Development

(1), LW (2), Both (3)

Condition of defect (Low,

Moderate, High)

1 5 3 1 1 1 Low20 5 3 1 1 1 Low100 5 3 1 1 1 Low

Total hours per year

ExposureArea occupied by

miners in day shift

Constant Prob. of Failure

Prob of annual occurrence of a FOG accident

Total Stopage (Days)

Hourly LW/Dev stopage cost

Total Stopage

Cost

8760 75 1 0.1 2.6E-06 0.13101254 52083.33333 163765.678760 75 20 0.1 5.1E-05 0.13101254 52083.33333 163765.678760 75 100 0.1 2.6E-04 0.13101254 52083.33333 163765.67

H&S Risk Category

Finacial Risk

CategoryPriority (3 Levels)

Response time - Ismet

- 7/5/2009Low Low Low 90 days

Moderate Low Moderate 35 DaysHigh Low High 21 Days

Evaluation of Monitoring System

Visual monitoring (including routine deputy and geotechnical inspections)

Tell-tales

GEL extensometers

Sonic probe extensometers

Borescope – Borehole camera

Borehole cameras (has been introduced only recently)

Seismic monitoring

GoafWarn

Warning lights and siren

Seismic geophone Start switch Standard nut for installation on roof bolts

Warning lights and siren

Seismic geophone Start switch Standard nut for installation on roof bolts

Support Standards (Corrosion Protection)

Further Systems Implemented

Routine geotechnical reviews of the critical areas

TARPs for drifts have been developed and implemented

Quality control procedures for the remedial support has been developed and will be implemented shortly

Acknowledgement

Anglo Coal Australia and Moranbah North Mines are

acknowledged to allow me to present this presentation

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Design of Remedial Support in Belt Drift, Moranbah...

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