boundary hill south project v - anglo...

Boundary Hill SoutH Project

Slope Stability Analysis

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SLOPE STABILITY ANALYSIS

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To: Alan Fredericks, Allan Heit

Cc: Andrew Toms, Peter McLure, Craig Lowe, Callide Geology, Centralised Geotech

Engineering, Bridget Perkins

Geotech Engineer: Thomas Hahn

Reviewed by: John Hoelle

Date: 02/01/2014

Subject: Callide Boundary Hill South Partings Dump Design – Life of Mine

EXECUTIVE SUMMARY: The dump design meets AAMC’s minimum stability acceptability criterion with a Factor of Safety comfortably above 1.2. The close proximity of the dump to creeks is a concern during the wet season considering the nature of the dumped material – a release of partings material may have an impact on the environment. Suitable erosion protection and capping of the dump have to be established. As experienced in the past, the ground conditions in this area can become very soft and boggy during the wet season. Floor preparation might become necessary before advancing the dump over natural topography. REQUEST: (by Alan Fredericks, Callide Mining Engineer):

• Provide a geotechnical stability analysis for the proposed Boundary Hill South dump LOM design. HISTORICAL / SLOPE INFORMATION:

• New dump at new location, no historical data available.

GOVERNMENT & ENVIRONMENTAL REGULATIONS: • Not issued in this report.

MODELLED PARAMETERS:

• Dump design – as supplied by site mining engineer: o 14° batter angle after rehabilitation. o Partly in-pit dumping over future Boundary Hill - South pits.

MODELLED ASSUMPTIONS:

• BMW Category 2 spoil strength parameters were assumed for the dump material, which are summarized in Table 1.

• Rock strength parameter for the weathered overburden, Callide Coal Measures and the coal are empirical Mohr-Coulomb.

• The modelled statistical variations in material strength for the probabilistic analyses assume a lognormal distribution and a standard deviation of 3 as lab data was not available.

•

Strata/Spoil Type Source γ kN/m3

C kPa

Φ °

Dump Unsaturated BMA Spoil Categories 18 40 30 Dump Saturated BMA Spoil Categories 20 18 24 Coal (fresh) SGRS Bowen Basin 13.5 30 35 Weathered Overburden Empirical Mohr-Coulomb 24 28 30 Callide Coal Measures Empirical Mohr-Coulomb 24 450 40

Table 1: Modelled Spoil/Rock Strength Parameters


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RESULTS SUMMARY: • The dump stability was assessed using Rocscience SLIDE for deterministic limit equilibrium

analysis. • Results for the Factor of Safety (FS) and Probability of Failure (PoF) are summarized in Table 2. • A sensitivity analysis was conducted for both the dump material and weathered overburden. • A circular failure mode was modelled for dump failures.

Section FSmin PoF Reference figure (page)

1 2.77 <5% Figure 1 (p.4) 2 2.85 <5% Figure 2 (p.5) 3 2.84 <5% Figure 3 (p.6) 4 2.92 <5% Figure 4 (p.7)

Table 2: Stability Analyses Summary for Dump Design CONCLUSIONS:

• The final dump design with a 14% overall slope angle is considered acceptable. • The conducted analysis cannot be used as an indication for erosion resistance. • As experienced in the past, the ground conditions in this area can become very soft and

boggy during the wet season. Floor preparation may become necessary where the dump is to be advanced over natural topography.

Operational risk:

• The highest risk to the operation is associated with the environmental impact of partings material being eroded by water run-off and the proximity to creeks.

Personnel safety risk:

• The risk of injury to personnel and equipment damage is low with the supplied design. • Site’s safety procedures should be followed at all times to manage the residual risk.

RECOMMENDATIONS: Risk Mitigation (controls):

• Dump to design. • Level and prepare the floor where necessary – do not dump into water or mud. • Establish drainage and erosion protection/capping. • Request MPD and MAD geotechnical requests for the individual stages of the dump.

MONITORING:

• OCEs to monitor for signs of instability during their shift routine - mainly slumping and cracking along the tip head.

• Operator and supervisor to conduct pre-start check and regular inspection of dump conditions during their shift.

• Dump to be re-graded where cracking is encountered. • Increase frequency of inspections if movement is observed. • OCE to inspect pit after blasts and major rain events. • If a change of conditions is observed: STOP, REASSESS AND SEEK GEOTECHNICAL

ASSISTANCE.


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APPENDIX 1 – LIMIT EQUILIBRIUM ANALYSES OF DUMP DESIGN 4-7 Figure 1. Section 1, Circular Spoil Failure Figure 2. Section 2, Circular Spoil Failure Figure 3. Section 3, Circular Spoil Failure Figure 4. Section 4, Circular Spoil Failure

APPENDIX 2 – DESIGN AS PROVIDED BY SITE ENGINEER 8-12 Figure 5. Plan View LOM Dump Design Figure 6. Sections 1 Figure 7. Sections 2 Figure 8. Sections 3 Figure 9. Sections 4


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APPENDIX 1 – LIMIT EQUILIBRIUM ANALYSES OF DUMP DESIGN

Figure 1. Section 1, Circular Spoil Failure ⇒ FSmin (Spencer) ~ 2.77


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APPENDIX 2 – DESIGN AS PROVIDED BY SITE ENGINEER

Figure 5. Plan View LOM Dump Design


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Figure 6. Sections 1


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