Slope Stability Monitoring through Impedance Imaging a - - PowerPoint PPT Presentation

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Slope Stability Monitoring through Impedance Imaging a - - PowerPoint PPT Presentation

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Slope Stability Monitoring through Impedance Imaging a collaboration between Alistair Boyle, Paul Wilkinson, Jonathan Chambers, Nolwenn Lesparre, & Andy Adler Spain 1998: Los Frailes Tailings Dam, Minas de Aznalcllar 1.5M m

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Slope Stability Monitoring Impedance Imaging

through

Alistair Boyle, Paul Wilkinson, Jonathan Chambers, Nolwenn Lesparre, Andy Adler

a collaboration between

&

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Spain 1998: Los Frailes Tailings Dam, Minas de Aznalcóllar

1.5M m³ tailings solids + 5.5M m³ acidic tailings water

Image: http://www.cerm3.mining.ubc.ca/Images/LosFrailes.jpg

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Provost, AB, Canada (2013) CP Rail freight train; 17 potash cars derailed, ~100m track destroyed.

Image & report: http://www.tsb.gc.ca/eng/rapports-reports/rail/2013/r13e0069/r13e0069.asp

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$

&

Slope Stability can represent effective mitigation: a monetary benefit an environmental risk

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σ

water content slope stability

Predictive: (?) 1) conductivity σ – water content:

  • Archie's Law (sandstone)
  • Waxman-Smits Equation (clay)

2) water content – slope stability:

  • Static Slope Stability Analysis based on

soil types and water content

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σ + ∂Ω

slope stability

Direct Monitoring: 1) Direct movement estimate from reconstruction

  • Online, remote monitoring
  • Cost effective equipment vs.

Laser range finding

σ

water content

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A Test Site

Hollin Hill, UK: A Slow Moving Landslide

March 2009 September 2008

[Paul Wilkinson et al.,”Geoelectrical Landslide Tracking”, EAGE2010]

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Absolute Solution

Measurements & Reconstruction

  • 32 electrode, linear array, downslope
  • Initial & final electrode positions & slope profile from RTK GPS

1) uniform initial σ est. based on best-fit, also used as fixed background σ 2) apparent resistivity = measurements scaled for geometry and stimulus

  • improved numeric stability by normalizing magnitudes

3) log σ: conductivity Jacobian (negativity constraint) 4) movement Jacobian by perturbation; alternate electrode sites in model 5) 2.5D: fine 3D fwd model, coarse 2D inv model, fitted to electrode pos. 6) absolute iterative Gauss-Newton solution

RTK: Real Time Kinematic; a differential GPS technology (± 1 - 4 cm absolute, 5mm relative to base station)

J ln σ=∂σ= ∂b ∂lnσ = ∂b ∂σ ∂σ ∂lnσ = ∂b ∂σ σ=J σσ

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J=.

Absolute Solution

Jacobian & Regularization Terms

J σσ J v J u

scaled adjoint Jacobian calculation In conductivity electrode perturbation downslope electrode perturbation cross-slope

Ju J v J σσ x=[ ln σ u v ]

T

u v

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Absolute Solution

Forward Solver Time

  • Movement perturbation is computationally slow (a fine mesh),
  • ne forward solution per Gauss-Newton iteration
  • Developed a generalized stim/meas improvement routine that

rearranges stimulus and measurements to minimize matrix

  • perations, skip redundant results, providing a transparent (to the

user) optimization.

  • Forward solution in 45 minutes becomes

3.75 minutes for rearrangement + 15 seconds per solution ... run times were two orders of magnitude faster

PM=N el DDoF Porig

N el=32, DDoF=2, PM≈37000 Timings on an Intel Xeon 2.6GHz, 8 cores, 64GB memory

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Reconstruction

Reasonable Agreement with “Ground Truth”

20 − 20 40 60 80 100 120 140 160 180 40 50 60 70 80 90 100 110 120 y [m] background=32.1 Ohm.m z [m] resistivity + electrode movement (U: down slope, scaled x10) at time B − 15 30 45 60 Ohm.m

WMF SSF

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  • Resistivity distribution agrees with geological

evidence

  • Estimated movement is in reasonable

agreement with GPS measurements

  • Further Refinement:

– Regularization and constraints for movement – Conjugate Gradient solver versus Gauss-Newton – Better iterative solver line search

Discussion

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Tiank You

Alistair Boyle, Paul Wilkinson, Jonathan Chambers, Nolwenn Lesparre, Andy Adler

a collaboration between

&

Slope Stability Monitoring Impedance Imaging

through

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Potash – water soluble potassium salts Main use: fertilizer largest producer: CAN worldwide 30M tons/yr

http://en.wikipedia.org/wiki/Potash Image: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/

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Geology

WMF: Whitby Mudstone Formations SSF: Staithes Sandstone and Cleveland Ironstone [Chambers et al. “Three-dimensional geophysical anatomy of an active landslide in Lias Group mudrocks, Cleveland Basin, UK” Geomorphology 125 (4) Feb 2011, p472–484]

Hand Drilling & Auguring