3-D Rock Slope Modeling

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Using digital photogrammetry to create 3-D rock slope models for virtual mapping and geotechnical characterization as part of a major highway project.

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3-D Rock Slope Modeling

  1. 1. Project challenges  Safely and efficiently map discontinuities along > 3000 ft of marginally stable rock slopes  Midway Curve MP66 (Golder Associates)  Hyak-Keechelus Dam (URS Corporation)  Predominantly fractured Cenozoic volcanic rocks  Only lower portions of slopes accessible on foot  Icy winter conditions and fast-track schedule for Midway Curve Milepost 66 project  Heavy summer traffic precluded lane closures for Hyak-Keechelus Dam project
  2. 2. Our approach  3-D rock slope modeling  Digital photogrammetry for model creation  Collaborative virtual discontinuity mapping  Geology + engineering team approach  Traditional fieldwork  Discontinuity orientation verification  Weathering  Joint aperture and filling  Intact rock quality
  3. 3. Why map discontinuities?  They control the mechanical behavior of fractured rock  Joints  Faults  Sedimentary bedding or volcanic flow contacts  Metamorphic foliation
  4. 4. Why photogrammetry?  1/2000 positional and 1° angular accuracy or better  More than adequate for most discontinuity mapping  Economical  Start-up cost is about 1/10 of a laser scanner  Off-the-shelf hardware easy to replace if damaged  Limits exposure to dangerous conditions  Photo fully integrated with 3-D mesh  Laser scanners have varying capabilities  Software with geologic mapping capabilities  Knowledge-based virtual fieldwork approach
  5. 5. Software choices Model Integrated Program Publisher creation? mapping? Sirovision CSIRO yes yes ShapeMetriX3D 3G yes yes Adam 3DM Analyst yes yes Technology PhotoModeler EOS limited no FotoG Vexcel yes no
  6. 6. • 6 megapixel photos • 125 feet long by 65 feet high • 7700 square feet • 425,523 xyz points Procedure • • 1.6 inch average spacing ±0.23 inch estimated RMSE Digital Photogrammetry Left Software Geometry Right
  7. 7. A typical project slope 55 feet 100 feet
  8. 8. Virtual structural mapping
  9. 9. 3-D discontinuity visualization
  10. 10. Field verification Computer Compass N = 171 poles N = 49 poles
  11. 11. Profiles and planes  Profile extraction along vertical planes with arbitrary strike  AutoCAD or Excel output  Import into Mathematica  Individual planes and traces can be plotted in 3-D to better understand discontinuity networks  Solid surface or transparent wire mesh
  12. 12. It’s not perfect, though • Highly oblique lines of sight produced poor to unusable results • Camera boom experiment didn’t work • Technology isn’t foolproof!
  13. 13. Summary  Practical 3-D data collection under challenging conditions  Virtual fieldwork is geologically attractive  Collaboration between geologists and design engineers  Custom development of additional capabilities  Profiles, joint system visualization, joint roughness coefficients  ACEC-WA Engineering Excellence Awards for MP 66  Silver: Originality or Innovative Application of New or Existing Techniques  Gold: Social, Economic, and Sustainable Design Considerations  See July 2007 issue of Civil Engineering for details  Will never eliminate the need to touch the rock  Joint filling, weathering, rock mass quality not conveyed in photos

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