CEE 437 Lecture 1

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CEE 437 Lecture 1

• September 29, 2005
• Thomas Doe

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Outline

• Course Introduction
• Geology and Engineers
• Brief History of Geology
• Global Structure
• Plate Tectonics
• The Rock Cycle and Material Differentiation

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Instructors

• Thomas Doe, Golder Associates
• MS, PhD, Geology, Mining Engineering, Wisconsin
• Fractures, Fracture fluid flow,
  geo-characterization, in situ stress
• Tunnels, hydroelectric projects, petroleum
  reservoirs, mine inflow
• William Dershowitz, Golder Associates
• MS, PhD MIT
• Fractures, fluid flow and rock mass stability
• Probabilistic simulation, fracture network
  modeling
• Radioactive waste RD, Petroleum reservoirs,
  mining applications (block caving)

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Class Overview

• Basic Treatment of Physical Geology
• Emphasis on Material Properties
• Emphasis on Pacific Northwest
• Geo-Characterization
• Geophysics
• Rock Engineering
• Geohydrology
• Not Covered
• Rivers, coastal geology

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Preliminary Syllabus
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What We Can and Cant Do

• Cannot do
• Provide enough to pass the state engineering
  geology test
• Provide a comprehensive engineering geology
  curriculum
• Can do
• Provide an appreciation of the importance of
  geology in engineering
• Provide a good overview of issues of Pacific
  Northwest significance

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Course Grading

• Quizzes, Exercises 35
• Paper 30
• Field Trip 25
• Class Participation 10

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Geology Subdivisions

• Academic earth history and fundamental
  processes
• Mineralogy, Petrology Rocks, mineral and
  origins
• Stratigraphy classification and definition of
  beds (sedimentary)
• Structure/Tectonics earth structure and origins
• Geochemistry
• Geophysics
• Geomorphology
• Applied applications to specific industries,
  engineering and environment
• Petroleum Geology/Geophysics
• Economic Geology (Minerals)
• Environmental Geology (geophysics, geochemistry)
• Hydrogeology
• Engineering Geology (geophysics, geochemistry)
• Geo-engineering
• Geotechnical Engineering Soil Mechanics
• Rock Mechanics as it says
• Geological Engineering

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Three Uses of Geology in Engineering

• Evaluate and predict the distribution of
  materials with specific engineering properties
• Subsurface evaluation uncertainty and
  properties
• Availability of materials
• Evaluate the actions of geologic processes on
  engineering structure
• Seismic
• Flood
• Slopes
• Evaluate the impact on engineering development on
  human and natural environments

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Rock as and Engineering Material

• Heterogeneous
• Highly variable
• Treat probabilistically, probability density
  functions
• Treat with geologic insight
• Anisotropic
• Directional
• Strength, elastic constants vary with direction
• Treat using tensor properties
• Scale Dependent
• Mineral/Crystalline scale
• Rock Sample Scale
• Rock Mass Scale

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Heterogeneity

• Rock properties vary from location to location
  (sometimes very drastically)
• Reduce by exploration
• Treat mathematically by probabilistic methods
• Reduce through geologic insight

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Anisotropy

• Depends on scale
• Mineral properties
• Rock fabric/texture
• Rock fracturing
• Properties affected
• Permeability
• Strength
• Elastic properties
• Represent properties as tensors

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Scale Effects

• Behavior depends on the scale of critical process
• Behavior depends on what aspect of geology
  controls critical behaviors

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Differentiation

• Geologic processes work by differentiation
• Crustal-scale processes
• Magmatic differentiation
• Sedimentary differentiation

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Case Study Snoqualmie Rock Slope Failures

• Rock slide on I-90, September 11
• 500 cubic yards
• Three fatalities
• Interstate closure for over 12 hours

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Why Did it Fail Now?

• Why was it stable?
• Fracture roughness
• Fracture persistence
• Why did it fail?
• Water inflow/pore pressure
• Weathering degradation
• Bad luck?

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Power Tunnels

• Case 1 Need for exploration and geologic insight
• Tunnel boring machine in granite
• Problem of buried channels
• Case 2 Hydraulic Jacking
• Water pressure exceeds in situ stress
• Water loss
• Slope failures

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Geology Brief History

• Origins in late 18th and early 19th Centuries
• Catastrophism and Uniformitarianism
• Age of Earth
• Uniformity of Processes
• Plate Tectonics Revolution (1950s to 1980s)
• Neo-Catastrophism

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Siccar Point Unconformity
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Crustal Composition

• Silica dominant rock component Quartz - pure
  silica
• Feldspars and Micas Al silicates with Ca, Mg,
  and K
• Fe, Mg silicates Olivines, Pyroxenes, Amphiboles

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Rock Cycle
Crystallization at depth or extrusion at surface
Magma
Melting
Igneous Rocks
Burial, metamorphism, recrystallization
Metamorphic Rocks
Weathering, Erosion
Sediments
Burial, metamorphism, recrystallization
Sedimentary Rocks
Lithification
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Bowen Reaction Series

• How to get many different rocks from one melt
  composition?
• Differentiation by selective crystallization and
  removal from system

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Differentiation in Crystallization
Slow Weathering
Quartz
Low Temperature, High Silica, Low Fe Mg
Muscovite
K-Feldspars
Biotite
Amphibole
Ca,Mg Feldspars
High Temperature, Low Silica, Hi Fe Mg
Pyroxene
Olivine
Fast Weathering
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Sedimentary Differentiation

• Sorting by Deposition Medium
• Sorting by Energy

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Crustal Composition

• Silica dominant rock component Quartz - pure
  silica
• Feldspars and Micas Al silicates with Ca, Mg,
  and K
• Fe, Mg silicates Olivines, Pyroxenes, Amphiboles

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Weathering Fates

• Feldspars to clays (clays, shales)
• Quartz endures (siltstones, sandstones)
• Calcium recirculated into carbonate minerals by
  organic processes (limestones)
• Consequence
• Over time, evolution of less dense more silicic
  continental crust

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Engineering Implications

• Style of geology and geo-engineering problems
  varies with plate tectonic setting
• Faulting, and structural complexity
• Maturity of materials varies with plate tectonics
  setting
• Higher degree of more stable materials from
  sorting by weathering
• Geohazards vary with plate tectonic setting

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Global Structure

• Based mainly on seismic information and meteorite
  compositions
• Crust 25-75 km depending varying under
  continents and oceans

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Global Structure
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Velocity Variation with Depth
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Development of Plate Tectonics

• Evidence from ocean floor magnetism and ages
• Evidence from seismicity
• Evidence from cross-continent correlations of
  rocks

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Global Seismicity
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Benioff Zone
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Sea-floor Spreading

• Mantle convection driven

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Seafloor Spreading Sediment Ages
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Evolution of Spreading Sea Floor Atlantic Analog
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Convergent Margins

• Ocean to Continent
• Continent to Continent

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Convergent Margin
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Convergent Margin Subduction Zone
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Light Si Rich Rocks
Heavy Si Poorer Rocks
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Evolution of Continents North American Craton
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North American Accretion