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

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

Oct 08, 2023 461 likes •860 views

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

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SLIDE 1

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. Siemens1, M. Gholami1, A. Khoshand1,

  • S. Fraser1, V. Paquin1, K.P. Weber1,
  • R. W. Beddoe2, H. Stewart3, T. Peet3

1Royal Military College of Canada 2York University 3Parks Canada Agency

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SLIDE 2

Jedway Mine Site

  • ds
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SLIDE 3

Jedway Mine Site

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SLIDE 4

Jedway Mine Site

Tailings piles Mill reservoir berm

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SLIDE 5

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

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SLIDE 6

Ongoing Instability

  • Active erosional slope banking on ocean

High tide 14-19 m Bare slope Tree erosion

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SLIDE 7

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?

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SLIDE 8

Site History From Air Photos

1962

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SLIDE 9

Site History From Air Photos

1970

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SLIDE 10

Site History From Air Photos

1980

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SLIDE 11

Site History From Air Photos

1994

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SLIDE 12

Site History From Air Photos

2005

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SLIDE 13

Site History From Air Photos

2010

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SLIDE 14

Site History From Air Photos

1962

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SLIDE 15

Site History From Air Photos

1970

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SLIDE 16

Site History From Air Photos

2010

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SLIDE 17

Landslide Mechanism

  • Tailings eroding into marine environment

– Toe eroded by waves causing over-steepening

14-19m

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SLIDE 18

Landslide Mechanism

  • Tailings eroding into marine environment

– Toe eroded by waves causing over-steepening

14-19m

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SLIDE 19

Landslide Mechanism

  • Tailings eroding into marine environment

– Toe eroded by waves causing over-steepening

Landslides

14-17m

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SLIDE 20

Geotechnical Site Characterization

  • Sampling

– 13 boreholes

  • Cone Penetration Testing

– Seismic Vs – Gamma fines content – Dissipation testing Hydraulic conductivity

  • Survey

– Total station – Drone

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SLIDE 21

Survey

  • 3D DEM of site
  • Total station
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SLIDE 22

CPT Results

  • Continuous profile
  • Soil properties
  • Groundwater

Gamma Probe

Photo Multiplier Tube CsI Crystal Gamma Ray Excitation Single or Triaxial Geophones (Vp & Vs) Thermistor (T) Friction Sleeve (fs) Pore Pressure Transducer (u) Cone Tip (qc) Load Cells Inclinometer (I) Porous Filter Element (u )

2

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SLIDE 23

Fine Tailings Classification

Gravel Sand Fines

  • Sandy-gravel profile
  • Note fine layer

at bottom of borehole

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SLIDE 24
  • Direct shear test

– c’=0, φ’=40o

Fine Tailings Shear Strength

φ’=40o

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SLIDE 25

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
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SLIDE 26

Seismic Hazard

www.earthquakescanada.nrcan.gc.ca/

M=4.5

  • Earthquakes from

17-Jan-2015 to 18-Jan-2016

– PGA=0.816 NBCC (2010)

Jedway Mine

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SLIDE 27
  • Magnitude >5.5 since 1985

Seismic Hazard

www.earthquakescanada.nrcan.gc.ca/

Jedway Mine

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SLIDE 28
  • Magnitude >5.5 in last 5 years

Seismic Hazard

www.earthquakescanada.nrcan.gc.ca/

Jedway Mine

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SLIDE 29

Cascadia Earthquakes

Caused tsunami in BC and Japan – Jan 26, 1700

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SLIDE 30

Stability Analysis

  • PGA=0
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SLIDE 31

Stability Analysis

  • PGA=0.1
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SLIDE 32

Stability Analysis

  • PGA=0.25
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SLIDE 33

Stability Analysis

  • PGA=0.5
  • Note FS<1
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SLIDE 34

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

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SLIDE 35

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

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SLIDE 36

Tsunami Notification Zones for BC

  • Jedway Mine located in Zone A
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SLIDE 37

Tsunami

  • Vicinity of tailings pile to open water

– Tsunami at high tide worse-case risk

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SLIDE 38

Summary

  • Uniquely located mine tailings pile
  • Ongoing instability causing environmental

effects

  • Risk of significant erosional event during

earthquake

  • Other risks:

– Liquefaction – Tsunami