Landslide Risk Assessment of a Tailings Pile at an Abandoned Mine - PowerPoint PPT Presentation

Landslide Risk Assessment of a Tailings Pile at an Abandoned Mine Considering Potential of Seismicity, Tsunami Waves, Liquefaction and Rainfall to Cause Large-scale Erosion G.A. Siemens 1 , M. Gholami 1 , A. Khoshand 1 , S. Fraser 1 , V. Paquin 1 , K.P. Weber 1 , R. W. Beddoe 2 , H. Stewart 3 , T. Peet 3 1 Royal Military College of Canada 2 York University 3 Parks Canada Agency

Jedway Mine Site • ds

Jedway Mine Site

Jedway Mine Site Tailings piles Mill reservoir berm

Unique Tailings Pile Location • Within “Gwaii Haanas” and owned by BC • Banking on Pacific Ocean – Wave erosion – Seismicity Iron ore mine – Liquefaction – Tsunami Tailings pile – Precipitation

Ongoing Instability • Active erosional slope banking on ocean Bare slope 14-19 m Tree erosion High tide

Environmental Effects • Ongoing instability eroding tailings into ocean – Tailings contain As, Cd, Co, Cu, Fe, Ni, Se, Zn – Elevated As and Cu in adjacent bay • Potential for large-scale erosional event?

Site History From Air Photos 1962

Site History From Air Photos 1970

Site History From Air Photos 1980

Site History From Air Photos 1994

Site History From Air Photos 2005

Site History From Air Photos 2010

Site History From Air Photos 1962

Site History From Air Photos 1970

Site History From Air Photos 2010

Landslide Mechanism • Tailings eroding into marine environment – Toe eroded by waves causing over-steepening 14-19m

Landslide Mechanism • Tailings eroding into marine environment – Toe eroded by waves causing over-steepening 14-19m

Landslide Mechanism • Tailings eroding into marine environment – Toe eroded by waves causing over-steepening 14-17m Landslides

Geotechnical Site Characterization • Sampling – 13 boreholes • Cone Penetration Testing – Seismic � Vs – Gamma � fines content – Dissipation testing � Hydraulic conductivity • Survey – Total station – Drone

Survey • 3D DEM of site • Total station

CPT Results • Continuous profile • Soil properties • Groundwater Gamma Probe Photo Multiplier Tube Gamma Ray Excitation CsI Crystal Single or Triaxial Geophones (Vp & Vs) Inclinometer (I) Thermistor (T) Friction Sleeve (fs) Load Cells Pore Pressure Transducer (u) Porous Filter Element (u ) 2 Cone Tip (qc)

Fine Tailings Classification • Sandy-gravel profile • Note fine layer at bottom of borehole Sand Gravel Fines

Fine Tailings Shear Strength • Direct shear test – c’=0, φ ’=40 o φ ’=40 o

Stability Analysis • Static slope analysis (no earthquake) – Agrees with field observations • Fails after oversteepening – Slow progression over last 40+ years • But there are other hazards

Seismic Hazard • Earthquakes from 17-Jan-2015 to 18-Jan-2016 – PGA=0.816 NBCC (2010) Jedway Mine M=4.5 www.earthquakescanada.nrcan.gc.ca/

Seismic Hazard • Magnitude >5.5 since 1985 Jedway Mine www.earthquakescanada.nrcan.gc.ca/

Seismic Hazard • Magnitude >5.5 in last 5 years Jedway Mine www.earthquakescanada.nrcan.gc.ca/

Cascadia Earthquakes Caused tsunami in BC and Japan – Jan 26, 1700

Stability Analysis • PGA=0

Stability Analysis • PGA=0.1

Stability Analysis • PGA=0.25

Stability Analysis • PGA=0.5 • Note FS<1

Seismic Stability Analysis • Larger earthquake changes failure mechanism – Potential for Large-scale event – 1:475 year event for Sa(0.2) – Equivalent to 10% probability of exceedance in 50 years

Liquefaction • Temporary loss of soil strength – Dynamic � after earthquake – Static � during infiltration • Similar to quicksand • Well-known for tailings piles • Will be evaluated using CPT data

Tsunami Notification Zones for BC • Jedway Mine located in Zone A

Tsunami • Vicinity of tailings pile to open water – Tsunami at high tide worse-case risk

Summary • Uniquely located mine tailings pile • Ongoing instability causing environmental effects • Risk of significant erosional event during earthquake • Other risks: – Liquefaction – Tsunami