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
ds Jedway Mine Site
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 Liquefaction Tsunami Precipitation Iron ore mine Tailings pile
Ongoing Instability Active erosional slope banking on ocean Bare slope Tree erosion 14-19 m 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
Continuous profile Soil properties ConeTec Groundwater Geotechnical, Environmental and Marine Site Investigation Services CPT Results GAMMA CONE PENETROMETER (GCPT) Gamma Probe Gamma Ray Excitation Photo Multiplier Tube CsI Crystal Single or Triaxial Geophones (V p &V s ) Inclinometer (I) Thermistor (T) Friction Sleeve (f s ) Load Cells Porous Filter Element (u ) 2 Pore Pressure Transducer (u) 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
Earthquakes from 17-Jan-2015 to 18-Jan-2016 PGA=0.816 NBCC (2010) Jedway Mine Seismic Hazard 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
PGA=0 Stability Analysis
PGA=0.1 Stability Analysis
PGA=0.25 Stability Analysis
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