3d geophysics for infrastructure · 2009, using geophysics to evaluate an embankment dam sinkhole...
TRANSCRIPT
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3D Geophysics
For InfrastructurePhil Sirles - Olson Engineering
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Geo-Modeling - Interpretation
How to Make
Sense of the
Model?
GeoVisualization
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Visualization – Out of Lego-Space
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Modeling and Analysis Package (MAP)
For Near-Surface Imaging
(i.e., Subsurface Characterization)
Modeling Definitions / Approach
VERY BASIC
3D Case Histories
Geotechnical Foundation Investigation –
Vail, CO
Roadway Subsidence Investigation –
Blue Ridge Pkwy., NC
Dam Stability / Sinkhole Analysis –
Knoxville, TN
Evaporite Karst Investigations –
sorry confidential site(s) – active projects
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3D Modeling Capabilities
Loading Small Strains - Seismic waves
Large Strains - static & dynamic load analysis, subsidence, slope failure
Discontinuities (NDE) Cracks, crack propagation, distinct layers, blocks of
arbitrary shape
Linear supports (NDE) soil nails, roof bolts, rebar
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3D Model Future Abilities
Optimized for seismic wave propagation,
for both forward and inverse modeling
Supports tomographic and holographic
inversion: Tolography
Soon - full-waveform seismic inversion (FWI)
Built-in signal processing capabilities via AI
TM
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Value of MAP Approach
The MAP approach combines & optimizes the discrete
element method of numerical modeling with particle flow
code, material point method, and finite differencing to
produce 2D & 3D MODELS of the subsurface
… NOT IMAGES of the subsurface.
These calibrated models can then be used for further
engineering evaluations (e.g., large-strain cracking,
subsidence, or slope-stability; or, small-strain static or
dynamic loading).
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Earthen Dam Investigation
Chilhowee Dam, TN
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Project Site
Chilhowee Dam was built
in 1957 on the Little
Tennessee River ~72km
(45 miles) south of
Knoxville
The dam is owned and
operated by Alcoa Power
Generating, Inc.
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Chilhowee Dam – Plan and Elevation Drawings
405m / 1330 ft
20m / 65 ft
Embankment EmbankmentConcrete Mid-section
& Powerhouse
u/s
d/s
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Chilhowee Dam – Typical Section
20m
Upstream-sloping
impermeable clay core
ShellShell
Filter
System
65ft
Crest Elev. 269.1m (883 ft)
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Gate
Posts
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N Gate Posts
Sinkhole
Borings
3D Grid Layout
- Blue = Geophone
- Red = Hammer Point
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START WITH BASE / CONCEPTUAL MODEL DEVELOPMENT – USE AS-BUILTS
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BUILD CARTESIAN GRID
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CROSS-SECTION MODEL DEVELOPMENT WITH
AS-BUILT DAM SECTIONS
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(5) 24-Ch DAQ’s
(120) 14-Hz Phones
(156) 10-blow SP’s
19,344 Ray Paths
FIELD WORK – 3D ACTIVE GRID OF GEOPHONES (120 ch’s)
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Ground Surface
B-2B Boring Location and NumberClay
Soft Clay
Gravel
Rockfill
Bedrock
Borehole Lithology
Surface Feature
LEGEND:
Geophone
Shot
Point
3D Model
– Ground
Limits
3D Model –
Limits
Velocity (ft/s *1000)
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3D Perspective View – Full MAP Model Space
A total of 246,310 elements were used,
with a total of 2,864,508 velocity links.
12 hour run-time for the
Desired 2-foot resolution
12,300 sq f t &
48 ft DOI
= 590,400 cubic feet.
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Prospective View
(Angle 100 )
Base of Low-
velocity
“trough”
Axis of Low-
velocity
“trough” o
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Elevation Slice
at 875 feet,
~middle of low-
velocity
‘trough’ (8’
below crest
elevation)Low-
velocity
“trough”
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Elevation Slice
at 875 feet,
~middle of low-
velocity
‘trough’ (8’
below crest
elevation)
Ground Surface
B-2B Boring Location and
Number
Clay
Soft Clay
Gravel
Rockfill
Bedrock
Borehole Lithology
Surface Feature
LEGEND:
Geophone
Shot
Point
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Elevation Slice
at 867 feet,
~base of low-
velocity
‘trough’ (16’
below crest
elevation)Low-
velocity
“trough”
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Elevation Slice
at 867 feet,
~base of low-
velocity
‘trough’ (16’
below crest
elevation)
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Chilhowee Won the “Construction Project of
the Year” award (for PB) at the USSD 2018
Annual Convention! Michael McCaffrey was
PB’s Principal Engineer (EOR)
McCaffery, M., Sirles, P., et.al.,,
2009, Using Geophysics to
Evaluate an Embankment Dam
Sinkhole – Chilhowee Dam, TN, in
Proceedings for the 29th Annual
USSD Conference
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Tight 3D Seismic Investigations
for 3D ‘Foundation’
Investigations (1-2 ac sites)
Karst Problems
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Tic-Tac-Toe Pattern: 96 Channels & 37 Shot points
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Ray Coverage Tic-Tac-Toe Pattern: 96 Channels & 32 Shot points
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Star Pattern: 96 Channels & 32 Shot points
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Ray Coverage Star Pattern: 96 Channels & 32 Shot points
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How to look “inside” a
3D volume of data:
Lots of plots?
Or …Slice and Dice
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Visual & Useful Results To
Give To The Client 3D Output
Oasis GeoSoft Montaj
Geophysics Package
• Data Analysis & Processing
• Visualization of Results
• FREE Viewer of (3D) Results
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Visual & Useful Results To
Give To The Client 3D Output
Oasis GeoSoft Montaj
Example Project Video OutputGeotechnical Site Characterization
(China Lake Naval Weapons Facility)
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MAP at a 22-ac Site to 250 feet below ground – 3D Imaging
SITE 3
Blue=Soil
Red=Hard Rock
Orange=Weathered Rock
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GRM Results Layered Solution:
Images (Cross-Sections)!
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Tomography Results Pixel Solution:
Images are Cross-Sections
Line 5
Weathered
Rock (Ls)
Competent Rock (Ls)
Colluvial
Soils (Qc)
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MAP Results 3D Model Output
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Prospective View
(Angle 100 )
Base of Low-
velocity
“trough”
Axis of Low-
velocity
“trough” o
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GeoSoft Results 3D Digital Output!
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CONCLUSIONS
Numerical Modeling is a powerful tool that
can / should be used (when appropriate)
Calibration and validation are available w/
geology and geotech info
Models deliver more than an image
MAP is an evolving software (not done
yet!)
Full waveform evaluation will be valuable
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