![Page 1: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/1.jpg)
1
Geophysical Applications to Subsurface Investigations:Reducing Uncertainty and Minimizing Risk
17th Annual Technical Forum for Geohazards Impacting Transportation in the Appalachian Region
August 15th-17th, 2017Blacksburg, Virginia
Presented By
Warren T. “Ted” Dean, P.G.Draper Aden Associates
![Page 2: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/2.jpg)
Why Perform Geophysical Testing?
• Sometimes provides information that you cannot get through invasive sampling.
• Fills in the blanks: Invasive sampling gives detailed information at one location; geophysics provides less detailed information over a broader area.
• Value: Reduces uncertainty and allows a targeted approach to invasive sampling.
Sinha, Thomas, Wang & Jung (2007) Penn State Study--Meta-analysis of cost-benefit studies of PADOT and VADOT projects
$1 spent up-front on geophysics saved (on average) $7 in total project cost
![Page 3: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/3.jpg)
Resistivity
• The property of a material to inhibit or resist the flow of electric current
• Resistivity versus Resistance
• Primary Factors that Affect Resistivity– Moisture Content– Material Grain Size
![Page 4: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/4.jpg)
Collecting 2-D Resistivity Data
4
4Multi-conductor resistivity cable
Electrode
Resistivity Meter
![Page 5: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/5.jpg)
Data Acquisition
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340
-5
0
5
10
15
20
25
30
35
40
45
50
AppliedCurrent
MeasuredVoltage
Bedrock
Soil
![Page 6: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/6.jpg)
Resistivity Model
25
50
75
100
125
150
175
200
250
275
300
350
400
450
500
750
1000
Resistivity Scale(ohm-meters)
Distance (ft)
Ele
vatio
n (ft
)
![Page 7: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/7.jpg)
Bedrock Surfaces
Resistivity Scale (ohm-meters)
0
25
50
75
100
150
200
250
300
350
400
450
500
1000
10000
100000
400000
0 100 ft
![Page 8: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/8.jpg)
Mapping Bedrock
1-11-5
1-101-15
1-201-25
2-12-5
2-102-15
2-202-25
3-13-5
3-103-15
3-203-25
4-14-5
4-104-15
4-204-25
5-15-5
5-105-15
5-205-25
6-16-5
6-106-15
6-206-25
6-306-35
6-40
7-17-5
7-107-15
7-20
7-25
7-307-35
7-40
8-18-5
8-108-15
8-20
8-25
8-30
8-35
8-40
9-19-5
9-10
9-159-20
9-25
9-30
9-35
9-40
10-110-5
10-10
10-15
10-20
10-25
10-30
10-35
10-40
11-111-5
11-10
11-1511-20
11-2511-30
11-35
11-40
12-112-5
12-1012-15
12-2012-25
12-3012-35
12-40
13-113-5
13-10
13-1513-20
13-2513-30
13-3513-40
14-114-5
14-10
14-15
14-2014-25
14-30
14-35
14-40
15-115-5
15-1015-15
15-20
15-25
Digitize the Bedrock SurfaceTo Obtain an X, Y, Z Data Set
0 200 400Feet
0 200 400
Feet
![Page 9: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/9.jpg)
Contour Map of Bedrock Surface
0 200 400
Feet
650
655
660
665
670
675
680
685
Elevation Scale (feet)
![Page 10: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/10.jpg)
When Trenching is Undesirable or Impractical
Crossing Sensitive Areas Such as:
Roads
Bodies of Water
Conservation Areas
Buildings
Cemeteries or Archaeological Areas
Horizontal Directional Drilling (HDD)Projects
![Page 11: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/11.jpg)
How thick is the overburden?
May effect casing estimates
If the drilling is to take place in the soil we may want to avoid the rock
What is the stratigraphy?
How competent is the rock?
Are there major fracture zones?
Common Questions to Answer on HDD Projects
![Page 12: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/12.jpg)
Mountain Crossing
al
ЄpЄc
pЄp
Gravel, sand, silt, and clay with boulder and cobble deposits in steeply dipping stream beds
Dark green, massive metamorphosed basalt containing local metavolcanic breccia. Gray-purple fine grained siltstone/phyllite interbedded with metabasalt near the top
Dark greenish gray, massive to foliated, garnet bearing, fine to medium grained granodiorite
Geologic MapProposed HDD
Entry Point
Proposed HDD Exit Point
![Page 13: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/13.jpg)
13
Exit
Entry Point
Proposed HDD Entry Point
Gravel, sand, silt, and clay with boulder and cobble deposits in steeply dipping stream beds
Dark green, massive metamorphosed basalt containing local metavolcanic breccia. Gray-purple fine grained siltstone/phyllite interbedded with metabasalt near the top
feet
WestResistivity Results and Interpretations
Possible limits of mapped alluvium deposits
East
Resistivity Scale (ohm-meters)
BR-B1
Soil
Rock
![Page 14: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/14.jpg)
Exit Point
ЄpЄc
Gravel, sand, silt, and clay with boulder and cobble deposits in steeply dipping stream beds
Dark green, massive metamorphosed basalt containing local metavolcanic breccia. Gray-purple fine grained siltstone/phyllite interbedded with metabasalt near the top
Dark greenish gray, massive to foliated, garnet bearing, fine to medium grained granodiorite
feet
West East
Resistivity Scale (ohm-meters)
Likely Fracture Zones
Possible limits of mapped alluvium deposits
HDD Path
Pedlar Formation
Catoctin Formation
![Page 15: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/15.jpg)
The Karst Environment
![Page 16: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/16.jpg)
Connecting the Surface to the Subsurface
0 20 40 60 80 100 120 140 160 180 200 220
-40
-20
0
sinkholes
Voids bedrock
soil
Solution channel connecting the sinkhole to the underlying void.
Resistivity (ohm-meters)
![Page 17: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/17.jpg)
Nashville, Tennessee
Detention Basin No.2
0 30 60 90 120feet
![Page 18: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/18.jpg)
Resistivity Lines
0 30 60 90 120feet
![Page 19: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/19.jpg)
Resistivity Results
0 30 60 90 120feet
Boring Explanation:
rubble fill
soil
rockvoid
0 50 100 150 200 250 300400
450
5002-25 2-20 2-15 2-10 2-5 2-1
0 50 100 150 200 250 300 350400
450
5003-25 3-20 3-15 3-10 3-5
3-1
0 50 100 200 300 500 25000 80000
Resistivity Scale (ohm-meters)
Potential air-filled voids
road
roadrecent
subsidence
recent subsidenceAT-2
(~2m south of line)AT-5
(@3-8.5)
AT-3 (~2m south of line)
Line 3
Line 2
Axes are in feet
![Page 20: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/20.jpg)
Blacksburg, VA
8-ft long 2x4
841 Crestwood Drive
sinkhole
subtle depressio
n
![Page 21: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/21.jpg)
Offset Throat
Crestwood Drive
N side of 841sinkhole
S side of 830likely sinkhole
throat
Possible air-filled voids
Line 4
![Page 22: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/22.jpg)
Electromagnetic Induction
• Also Called Terrain Conductivity: measure of how well the subsurface conducts an electric current.
• Applications:• Landfills and trenches• Buried drums, tanks, utilities• Buried structures
![Page 23: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/23.jpg)
Structures and Utilities
-22-20-18-16-14-12-10-8-6-4-20246810121416182022
In-Phase(ppt)
![Page 24: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/24.jpg)
Ground Penetrating Radar
Applications:• Location of Buried
drums or tanks• Location of Buried
Utilities• Archeological-forensic
studies• Reinforcement Steel• Subslab Voids
![Page 25: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/25.jpg)
2.5-3 Feet Depth Slice
![Page 26: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/26.jpg)
2.5-3 Feet Depth Slice with EM Overlay
![Page 27: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/27.jpg)
Concrete Reinforcement and Utilities
0.25-0.5 Feet
1.0-1.25 Feet
GRID 1X
Y
Proposed drill hole
![Page 28: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/28.jpg)
Sub-slab Voids
1.25 – 1.5 feet
Y-59
Bottom of BlocksVoid Joints
![Page 29: Geophysical Applications to Subsurface Investigations ......$1 spent up-front on geophysics saved (on average) $7 in total project cost . ... connecting the sinkhole to the underlying](https://reader033.vdocuments.us/reader033/viewer/2022050601/5fa8d02b7f8d9c71c242b34a/html5/thumbnails/29.jpg)
Thank You!
• Questions?