Practices and Challenges. For Open Pit Geotechnical Characterization, Design and Execution

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1 Practices and Challenges For Open Pit Geotechnical Characterization,

2 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

3 Practices and Challenges for Geotechnical characterization, Deep Open Pits Robotham, 2011 Enabling Technologies Workshop - SLC, March

4 Deep Open Pits Batu-Hijau Phase 7 orig rev 11 now to 43 LOM 31 now Enabling Technologies Workshop - SLC, March

5 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

6 SWOT Analysis Observations Open Pits Strengths and Opportunities Mine Planning - optimization process - site specific opportunities Relevant Experience Operations and People Analysis Tools analytical and numerical Performance Monitoring instrumentation 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 Enabling Technologies Workshop - SLC, March

7 Design and Execution SWOT Analysis Observations Underground Mines 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 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 Enabling Technologies Workshop - SLC, March

8 Is enough factual data available for geomechanics design and reliable operational performance? - Some examples Enabling Technologies Workshop - SLC, March

9 Batu Hijau Enabling Technologies Workshop - SLC, March

10 Geomechanics Practice vs Performance xxx Enabling Technologies Workshop - SLC, March

11 Batu Hijau Domain 1 mapping vs oriented core Enabling Technologies Workshop - SLC, March

12 Gold Copper Project at Feasibility Study Level Enabling Technologies Workshop - SLC, March

13 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? Enabling Technologies Workshop - SLC, March

14 From: Geotechnical Considerations in Underground Mines; Guideline; MOSHAB Doc #ZME723QT SUGGESTED PERCENTAGE OF CORED BORE HOLES TO BE GEOTECHNICALLY LOGGED Stage of mine development Prefeasibility study Feasibility study Operating mine Suggested percentage geotechnically logged % % % 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. Enabling Technologies Workshop - SLC, March

15 Hard Rock? Enabling Technologies Workshop - SLC, March

16 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 Enabling Technologies Workshop - SLC, March

17 Mine dewatering/ slope depressurization Weak-deformable rock and soil masses are susceptible to instability due to groundwater pressurization. Enabling Technologies Workshop - SLC, March

18 East Wall - KCGM Oct mm rain June 2011 nearby blast

19 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

20 Structural Control, previously unknown Structural Control? Enabling Technologies Workshop - SLC, March

21 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. Enabling Technologies Workshop - SLC, March

22 Summary 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. Enabling Technologies Workshop - SLC, March

23 Conclusions 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. Enabling Technologies Workshop - SLC, March

24 Big meeting end report Enabling Technologies Workshop - SLC, March