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 • Conclusions – Ideas for future work – Remote sensing? 2

Background • Tailings - Fine-grained mine waste ( Tail-end) • Leaving extraction processes in a slurry • Impoundments – Dams – Similarities/Differences to water retention dams 3

Tailings dam failures Germano Mine, Nov. 5 2015 Bento Rodriguez, Brazil Aznalcóllar, Spain Cerro Negro, Chile Stava, Italy Kolontár, Hungary 1985 2003 1998 2010 Taoshi, China Mount Polley, Canada Merriespruit, South Africa Aitik, Sweden 1994 2000 2008 2014 4

Background cont. • Regulations, Guidelines & Handbooks – Stability analyses (Factor of Safety) – Dam surveillance, geotechnical instrumentation • Tailings management – Design & Stewardship • Stability & Corresponding dam performance 5

Seepage Background cont. Deformation FoS • Stability & Corresponding dam performance Pore water pressure Field data Time 6

Aitik Tailings Facility • Open pit, copper mine – Gällivare, Sweden • Dams from 1966 (mining from 1968) • Tailings hydraulically transported • History: 2013 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 7

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

Numerical modeling • PLAXIS 2D (FEM) • Cross-section, Aitik dam E-F 9

Numerical modeling • Soil regions: • Staged construction model: – As-built drawings Historical events 1992-2013 – CPTu & Sample locations Planned events + Safety 2014-2024 – Airborne data surveys 1992 2007 2013 10

Numerical modeling • Constituve modeling – Tailings – Hardening Soil model – Other materials – Mohr-Coulomb model Triaxial Oedometer Hardening Soil: 𝑣𝑠 Mohr-Coulomb: 11

• ” SoilTest ” – calibration of model parameters to lab. results Lab – Solid lines SoilTest simulation – Dashed lines Oedometer: Triaxial: Oedometer Test Axial Strain, ε 1 [%] 12

Numerical modeling • Stability – Factor of Safety – Recommended value 1.5 (Swedish guidelines) 13

• To maintain the safety – Increased rockfill with time – Support plan 23-24 22-23 21-22 20-21 19-20 13-14 15-16 20-21 18-19 19-20 14-15 16-17 17-18 21-22 19-20 14

Agreement to field observations • Horizontal deformations – Inclinometer installed 2007 – Measured twice per year Photo: F. Jonasson 2015 15

• Field data: 16

Agreement to field observations • Field observations vs. Simulations – Simulated period 1992-2013 – Period for comparison 2007-2013 • Good agreement PLAXIS • Confirms the model • The model can be used for prediction of future deformations IN SITU - Coupled to computed stability 17

Summary 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 18

Modeling (FEM) Surveillance DAM SAFETY INTERPRETATION 19

Modeling (FEM) Surveillance DAM SAFETY INTERPRETATION Inclinometers - displacements vs. depth Modeling (FEM) Surveillance Remote sensing? Complementary monitoring ? ”Real -time ”? Accuracy? DAM SAFETY INTERPRETATION 20