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GE 343 SUBSURFACE EXPLORATIONCH 3 – Surface Mapping
Text Ch. 4.
Dr. Norbert H. MaerzMissouri University of
Science and Technology(573) 341-6714
Instructional Objectives
1. Plan a site investigation limited to surface exploration
2. Select and justify what you would look for given a site investigation scenario
3. Generate a test pit log
4. Classify soil
5. Measure strike and dip of discontinuities and plot on a stereonet
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What do we look for?
• Geological mapping of rock and soil type (GMU’s)
• Structural mapping (discontinuities)• Identifying geomechanical properties• Look for the extraordinary things,
(geological hazards)• Ground truthing of interpretations made
from imagery/maps/reports
GMU: (DEFINITION) –Geotechnical mapping unit:
1) Is an extent of rock that is similar enough to be considered a single mapping unit for geotechnical purposes.
2) This may cross different geological formations, or subdivide them.
3) The unit may be more or less inclusive for different purposes.
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REV
• Concept of Representative Elemental Volume (REV)
• Rock material vs Rock Mass
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Engineering Geological Mapping
1. Stratigraphy2. Exploration location3. Accessibility4. Key outcrops5. Water6. Existing Slopes7. Material Sources8. Geological Constraints9. Environmental Considerations
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General Proc. For Eng. Geol Mapping
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Geological Mapping
• Test pits, trenches, shafts
• Rock structure mapping
• Tunnel silhouette photography
• Materials survey
• Field verification of aerial interpretations
Example of a Geologic
Map
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Test Pits, Trenches, Shafts
• Test Pits1. Backhoe or excavator2. Describe and sample spoil and pit walls3. 12-20 deep or refusal4. 5’ depth limit on entry OSHA5. Standpipe6. “Undisturbed Sample”7. Strength Characterization8. Backfill immediately
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Picture(s) from the collection of Dr. J. A. Franklin Picture(s) from the collection of Dr. J. A. Franklin
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Test Pit Log
AASHTO Man. Sub. Inv. Picture(s) from the collection of Dr. J. A. Franklin
Geotechnical Control Office, Hong Kong- Strength
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Unified Soil Classification
• Developed by Casagrande 1952
• Universally used
• Course grained soils classified according to size and size distribution
• Fine grained soils classified according to Plasticity
• Common set of symbols
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Ruler or Tape measures
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Color Charts
Pocket Penetrometer
http://www.benmeadows.com/store/product_group.asp?dept_id=8743&parent_id=398
TorvanePocketPeneP
Pocket Penetrometer
TorvaneQuick
settling test
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Quick settling
test(Clay/silt)
Quick settling
test(Sand/silt)
Test Pits, Trenches, Shafts
• Trenches1. Backhoe or excavator, or bulldozer
2. Same as test pits, but typically shallower and longer
AASHTO Man. Sub. Inv. Picture(s) from the collection of Dr. J. A. Franklin
Trenches
Picture(s) from the collection of Dr. J. A. Franklin
Exploratory Shafts
• Adits and shafts
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Rock Structure Mapping
• Observing, locating, measuring, and recording:– Lithologies and Contacts
– Rock Discontinuities
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Bedrock Stratigraphy
Geotechnical Control Office, Hong Kong- Strength Color / Texture
Weathering / Alteration Rock Name / Structure
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Discontinuities Weathering
Orientation: Measurement
Measuring Strike
Measuring Strike
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Measuring Dip
Measuring Dip
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Surface Mapping vs. DrillingAdvantages and Disadvantages
• weathering often accentuates features
• can see large scale features
• not have the orientation bias of boreholes
• typically not at the right place and depth
• weathering often obscures features
• weaker geomechanical properties on surface (not representative)
Picture(s) from the collection of Dr. J. A. Franklin
Tunnel Silhouette Photography
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Case Study – Q system to predict overbreak at
Aquamilpa
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Relationships
• STATISTICAL RESULTS: Rock mass quality (Q) is more likely to be the cause of overbreak, while explosive energy (PPF) is more likely to be the cause of underbreak
)(log55.207.1512.0(%) QPPFOverbreak
)log(72.014.1133.9(%) QPPFUnderbreak
Materials Survey
1. Cut and fill
2. Aggregates
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Field Verification of Aerial Interpretations
“Ground Truthing”