2ndday exp09 operation management and geotechnical control of tailings deposits dirk van zyl 19 6

Operation, Management, and Geotechnical Control of Tailings Deposits Dirk van Zyl, PhD, PE, Peng Professor, Chair of Mining and the Environment

University of British Columbia Canada

Tailings Management Practice

Slurry Tailings Management

Upstream Construction

Downstream Construction

Centerline Construction

Thickened Tailings •

Thickened tailings are tailings partially dewatered to a dense, non-segregating slurry.

• Thickened tailings are typically disposed in a conical shape, from the center of the cone • Bleeding water and runoff are typically collected in a pond at the lowest point of the facility • Diversion channels may be required Peak Gold Mine, Australia.

Paste Tailings

Ref: 1) Surface Disposal of Paste Tailings at the Bulyanhulu Gold Mine, Tanzania. Paper by James A. Theriault, John Frostiak, Don Welch.

2) www.tailings.info/disposal/paste.htm

Filtered Tailings

Greens Creek Mine, Admiralty Island, Alaska

How do Tailings Facilities Fail?

Statistics of Tailings Failures, ICOLD and UNEP, 2001

Fault Tree Approach for Evaluating Stability of Tailings Facility

Fault Tree for Overtopping

Mount Polley Failure

Mount Polley TSF Failed on August 4, 2014

The estimated volumes of materials displaced by the breach: • Supernatant water 10.6Mm3 • Tailings Slurry: tailings solids 7.3Mm3; interstitial water 6.5Mm3 • Construction materials 0.6Mm3 http://www.imperialmetals.com/s/Mt_Polley_Update.asp?ReportID= 671041

Photos from Vancouver Sun

Tailings near the Likely, BC August 5, 2014. Hazeltine Creek in background (Vancouver Sun)

Independent Expert Engineering Investigation and Review Panel •

Appointed on August 18, 2014 – Norbert R. Morgenstern (Chair) CM, AOE, FRSC, FCAE, Ph.D., P.Eng. – Steven G. Vick, M.Sc., P.E. – Dirk van Zyl, Ph.D., P.E., P.Eng.

• Final report released on January 30, 2015 https://www.mountpolleyreviewpanel.ca

Review of Information

Conclusions Cause of the Failure •

The breach of the Perimeter Embankment on August 4, 2014 was caused by shear failure of dam foundation materials when the loading imposed by the dam exceeded the capacity of these materials to sustain it. The failure occurred rapidly and without precursors.

•

Deposited in a complex geologic environment, the weaker glaciolacustrine layer was localized to the breach area. It went undetected, in part because the subsurface investigations were not tailored to the degree of this complexity. But neither was it ever targeted for investigation because the nature of its strength behaviour was not appreciated.

Conclusions Cause of the Failure Cont’d.

•

Throughout, the design investigations took note of the stiff, dense character of foundation soils and used corresponding strength properties in stability analyses.

•

But it was not recognized that this character would change, with a corresponding change in strength behaviour under the increased loading as the dam grew higher.

•

Adding to the antecedent foundation conditions was the unprecedented steepness of the 1.3H:1V Perimeter Embankment slope.

Site Surface Mapping

Contours of Upper GLU Thickness

Recommendations • 1. •

BAT (Best Available Technologies) To implement BAT using a phased approach BAP (Best Available Practices)

2.

To improve corporate governance

3.

To expand corporate design commitments

4.

To enhance validation of safety and regulation of all phases of a TSF

5.

To strengthen current regulatory operations

6.

To improve professional practice

7.

To improve dam safety guidelines

Basics of BAT 1. Eliminate surface water from the impoundment

2. Promote unsaturated conditions in the tailings with drainage provisions

3. Achieve dilatant conditions throughout the tailings deposit by compaction

Recommendations • 1. •

BAT (Best Available Technologies) To implement BAT using a phased approach BAP (Best Available Practices)

2.

To improve corporate governance

3.

To expand corporate design commitments

4.

To enhance validation of safety and regulation of all phases of a TSF

5.

To strengthen current regulatory operations

6.

To improve professional practice

7.

To improve dam safety guidelines

Translating the Recommendations To improve corporate governance

Corporate management must be committed to tailings safety – MAC actions

To expand corporate design commitments

Tailings design details must be well developed for permitting – MEM actions

To enhance validation of safety and regulation of all phases of a TSF

Appointment of Independent Tailings Review Boards as appropriate – MEM actions

To strengthen current regulatory operations

Review all tailings dams for weak foundations, water balance and filter design – MEM actions

To improve professional practice

Develop guidelines for site characterization – APEGBC actions

To improve dam safety guidelines

Review of Canadian Dam Association Guidelines – CDA actions

What about the local communities, especially the First Nations?

Peter Sandman defines risk as:

Risk = Hazard + Outrage He identifies 20 components and factors that can cause “Outrage�

Sandman, Peter M. (1993) Responding to Community Outrage: Strategies for Effective Risk Communication, American Industrial Hygiene Association, Fairfax, VA., 142 pp.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Is it Voluntary or Coerced?

Is it Natural or Industrial?

Is it Familiar or Exotic?

Is it Not Memorable or Memorable?

Is it Not Dreaded or Dreaded?

Is it Chronic or Catastrophic?

Is it Knowable or Not Knowable?

Is it Controlled by Me or by Others?

Is it Fair or Unfair?

Is it Morally Irrelevant or Morally Relevant?

Can I Trust You or Not? Is the Process Responsive or Unresponsive?

13. Effect on Vulnerable Populations 14. Delayed vs. Immediate Effects 15. Effect of Future Generations 16. Identifiability of the Victim 17. Elimination vs. Reduction 18. Risk-Benefit Ratio 19. Media Attention 20. Opportunity for Collective Action

What emotions are expressed?

Disappointment Lost of trust Anger Outrage

Recommendations will help to address outrage What else should be done on a project specific basis?

Mining is a Waste Management Activity.

Profits are only possible once Waste Management has been taken care of.

The Safety Case, not the Cost Case, should be the focus.