SLIDE 1
Outline
- Background
- Aitik Tailings Facility
– Tailings properties – Numerical modeling – Field observations
- Anticipated dam performance
- Conclusions
– Ideas for future work – Remote sensing?
2
Aitik case study dam safety interpretation via modeling and - - PowerPoint PPT Presentation
Aitik case study dam safety interpretation via modeling and - - PowerPoint PPT Presentation
Aitik case study dam safety interpretation via modeling and surveillance Roger Knutsson Outline Background Aitik Tailings Facility Tailings properties Numerical modeling Field observations Anticipated dam performance
SLIDE 2
SLIDE 3
Background
- Tailings - Fine-grained mine waste (Tail-end)
- Leaving extraction processes in a slurry
- Impoundments – Dams
– Similarities/Differences to water retention dams
3
SLIDE 4
Tailings dam failures
4 Stava, Italy Merriespruit, South Africa Kolontár, Hungary Mount Polley, Canada Aznalcóllar, Spain Aitik, Sweden Taoshi, China Cerro Negro, Chile
1985 1994 1998 2000 2003 2008 2010 2014
Germano Mine, Nov. 5 2015 Bento Rodriguez, Brazil
SLIDE 5
Background cont.
- Regulations, Guidelines & Handbooks
– Stability analyses (Factor of Safety) – Dam surveillance, geotechnical instrumentation
- Tailings management
– Design & Stewardship
- Stability & Corresponding dam performance
5
SLIDE 6
Background cont.
6
- Stability & Corresponding dam performance
Deformation Pore water pressure Seepage
FoS
Field data Time
SLIDE 7
Aitik Tailings Facility
- Open pit, copper mine
– Gällivare, Sweden
- Dams from 1966 (mining from 1968)
- Tailings hydraulically transported
- History:
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2013 7
SLIDE 8
Tailings properties
- Field investigation, Aitik 2013
- Samples studied in lab.
- Mechanical properties determined by:
– Triaxial tests (Consolidated Drained) – Direct Simple Shear tests (Consolidated Drained) – Direct Simple Shear tests (Consolidated Undrained) – Standard Oedometer testing (incremental loading)
8
SLIDE 9
Numerical modeling
- PLAXIS 2D (FEM)
- Cross-section, Aitik dam E-F
9
SLIDE 10
- Soil regions:
– As-built drawings – CPTu & Sample locations – Airborne data surveys
Numerical modeling
- Staged construction model:
1992-2013
Historical events
2014-2024
Planned events + Safety
10
1992 2007 2013
SLIDE 11
- Constituve modeling
– Tailings – Hardening Soil model – Other materials – Mohr-Coulomb model
11
Hardening Soil: Oedometer Triaxial Mohr-Coulomb:
Numerical modeling
𝑣𝑠
SLIDE 12
- ”SoilTest” – calibration of model parameters to lab. results
12
Triaxial:
Axial Strain, ε1 [%]
Oedometer:
Lab – Solid lines SoilTest simulation – Dashed lines
Oedometer Test
SLIDE 13
Numerical modeling
- Stability – Factor of Safety
– Recommended value 1.5 (Swedish guidelines)
13
SLIDE 14
- To maintain the safety
– Increased rockfill with time – Support plan
14
19-20 19-20 21-22 13-14 16-17 14-15 15-16 19-20 20-21 21-22 22-23 23-24 17-18 18-19 20-21
SLIDE 15
Agreement to field observations
- Horizontal deformations
– Inclinometer installed 2007 – Measured twice per year
15
Photo: F. Jonasson 2015
SLIDE 16
16
- Field data:
SLIDE 17
17
Agreement to field observations
- Field observations vs. Simulations
– Simulated period 1992-2013 – Period for comparison 2007-2013
- Good agreement
PLAXIS IN SITU
- Confirms the model
- The model can be used for prediction
- f future deformations
- Coupled to computed stability
SLIDE 18
Summary
18
General methodology:
- Field and laboratory investigation
- Numerical modeling
– Advanced constitutive modeling – Agreement to field observations
- Safety analyses
– Plan for strengthening actions
- Anticipated dam performance
– Future events
SLIDE 19
19
Modeling (FEM) Surveillance DAM SAFETY INTERPRETATION
SLIDE 20
20
Modeling (FEM) Surveillance DAM SAFETY INTERPRETATION Inclinometers - displacements vs. depth Remote sensing?
Complementary monitoring? ”Real-time”? Accuracy?
Modeling (FEM) Surveillance
DAM SAFETY INTERPRETATION