successes and needs for large open pit mines – the lop project
TRANSCRIPT
Practices and Challenges
For Open Pit Geotechnical Characterization, Design and Execution
Enabling Technologies Workshop - SLC, March 2013 2
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Geomechanics Risk Management Perspective - Mining Context
Sizing up geomechanics risk in mining:
Mining is considered to be a high risk (potential) business in terms of
both safety and economics. There is always the possibility that an
excavated slope, or underground excavation, may not perform as
predicted and could fail with significant and even catastrophic results.
Enabling Technologies Workshop - SLC, March 2013 3
Practices and Challenges for Geotechnical characterization,
Design and Execution Deep Open Pits
Robotham, 2011
Enabling Technologies Workshop - SLC, March 2013 4
Practices and Challenges for Geotechnical Characterization,
Design and Execution Deep Open Pits
Batu-Hijau – Phase 7 orig 1,050m @37º rev 930m @34º
11 now to 43 LOM
31 now
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Factors effecting opening stability
- Depth
- Stress levels due to depth (Virgin stress)
- Stress levels associated with mining
- De-stressing after mining
- Rock mass strength
- Major structures
- Size
- Stress direction
- How close are other openings (interaction distance)
- Ground Support requirements
- Seismic activity
Enabling Technologies Workshop - SLC, March 2013 6
Practices and Challenges for Geotechnical Characterization,
Design and Execution SWOT Analysis – Observations Open Pits
Threats and Weakness
Geological Context for Slope Design
Groundwater and Surface Water Management – Seasonal Changes
Executing the Mine Plan
- mine the plan, satisfy design assumptions
- operational controls – cleanup, blasting
Strengths and Opportunities
Mine Planning
- optimization process
- site specific opportunities
Relevant Experience – Operations and People
Analysis Tools – analytical and numerical
Performance Monitoring instrumentation
Enabling Technologies Workshop - SLC, March 2013 7
Practices and Challenges for Geotechnical Characterization, Design
and Execution SWOT Analysis – Observations Underground Mines
Threats and Weakness
Geological context and uncertainty – material influence on reserve model/ mine plan
Structural geology – changes to mine layouts; ad-hoc design changes are common
Mine sequence changes to compensate for production issues
- stopes designed beyond feasible limits; standup time excedances;
- delayed backfilling
- blasting usually not optimized (ability and tools are there; but not a priority)
Educated, skilled and experienced personnel
Strengths and Opportunities
Ground (Rock) Support
Backfill for operational flexibility; can allow for mining in the worst
ground (UH cut/fill)
Mine design using 3D methods
Performance Monitoring instrumentation
Automation that reduces exposure to Operators; Safety
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Is enough factual data available for geomechanics
design and reliable operational performance?
- Some examples…
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Batu Hijau
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Geomechanics – Practice vs Performance xxx
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Practices and Challenges for Geotechnical Characterization,
Design and Execution Batu Hijau – Domain 1 mapping vs oriented core
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Gold – Copper Project at
Feasibility Study Level
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Example of a structural model
For an ultimate design pit for a
Copper Project at the FS level.
Design final pit > 1 km deep;
Interpretive focus on orebody;
Model of major structure
representative of the ore
zone, but what about the
waste rock zone to be
excavated to access ore?
14 Enabling Technologies Workshop - SLC, March 2013
SUGGESTED PERCENTAGE OF CORED BORE HOLES TO BE
GEOTECHNICALLY LOGGED
Stage of mine development Suggested percentage geotechnically logged
Prefeasibility study Feasibility study Operating mine
25 - 50 % 50 - 100 % 25 - 75 %
Modern down hole geophysical logging methods may be used to extract some
geotechnical data from diamond drill and, less optimally, RC hole walls. These down
hole logging techniques should be calibrated in known ground conditions by comparing
the results obtained from conventional geotechnical logging of whole diamond drill core
with those obtained from down hole geophysical logging.
Regardless of the actual number of holes geotechnically logged, what is of
fundamental importance is that those holes that are geotechnically logged
constitute a representative sample of the ground conditions found in the ore
zone(s) and the wall rocks of a potentially mineable deposit.
From: Geotechnical Considerations in Underground Mines; Guideline;
MOSHAB Doc #ZME723QT
Practices and Challenges for Geotechnical Characterization,
Design and Execution
15 Enabling Technologies Workshop - SLC, March 2013
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Hard Rock?
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Practices and Challenges for Geotechnical Characterization,
Design and Execution Groundwater – Open Pits
Risk Factors - Open Pits
Pore pressure increases reduce effective stress
Contributes to deformation response during mine development
Contributes to block deformation during blasts
In combination with deficient surface water management; contributes to:
Uncontrolled pit inflows
Pit flooding
Wet blasting
Impacts to access, production delays, and increased mining costs
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Practices and Challenges for Geotechnical Characterization,
Design and Execution
Mine dewatering/ slope depressurization
Weak-deformable rock and soil masses are
susceptible to instability due to groundwater
pressurization.
East Wall -
KCGM
Oct 2011 80 mm rain
June 2011 nearby blast
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Fiji is the basal fault of the
October 2011 slip, previously
unknown
- it took 9 months to
stabilize the wall, mine out
failed debris and put the
ramp back into service
Reliance fault is interpreted
from intersection of 4 core
holes
- modeled to undercut the final
east wall
Enabling Technologies Workshop - SLC, March 2013 20
Structural Control,
previously unknown
Structural Control?
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Challenges associated with
mining into voids can be
mitigated
GPR appears to be promising, but
reliability using GPR falls short of
requirements, where probe drilling
is currently the standard.
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Enabling Technologies Workshop - SLC, March 2013 22
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Low probability - high consequence events such as slope instabilities and
ground fall in underground mines will continue to occur in the mining
industry; the most common reasons:
Decision to accept risks associated with the selected design option
Inadequate geological characterization
Inadequate design consideration (long term vs. short term)
Assumptions associated with mine design recommendations not adequately
implemented (groundwater, blasting, scaling, clean-up)
Failure to mine the plan
Poor operating practices and QC (blasting, scaling, cleanup, backfill,
deficient ground support)
etc., etc.
Summary
Enabling Technologies Workshop - SLC, March 2013 23
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Enlightened companies are improving in geotechnical effort as design and
operational components of their business.
We as geotechnical practitioners will continue to be challenged to determine
the level of data and analysis required to achieve adequate level of design
and performance reliability; and be able to communicate and sell those needs
to Mine Operations and Project Managers.
Conclusions
Enabling Technologies Workshop - SLC, March 2013 24
Practices and Challenges for Geotechnical Characterization,
Design and Execution
Big meeting – end report