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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

norbert@mst.edu

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

Franklin and Dusseault Franklin and Dusseault

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

Franklin and Dusseault

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”