Engineer and Engineering Geologist

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Engineer and Engineering Geologist

• What should you be able to do as an engineer who
  works together with an engineering geologist?

• You need to be able to communicate!!!
• Read Geological Maps
• Predict the geological conditions at depth from
  map and drill hole logs
• Construct a cross section of the subsurface
  geology

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Engineer and Engineering Geologist

• understand
• geological processes
• natural hazards
• weathering and products
• evaluate positive and negative conditions
• relate to planners and politicians
• economic implications

• What should you be able to do as an engineer who
  works together with an engineering geologist?

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Can we choose where it is best to build?
Hazardous areas?

• earthquakes are common?
• volcanic eruptions are common?
• landslides are common?
• etc.

• Don let anyone live in Japan or San Francisco
• It is too hazardous from a geological point of
  view!!

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Your job as Engineer

• Recognize problems
• Propose an engineering solution
• If you want to build (X) then you must build in
  the following way (Y)

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There is an engineering solution to any
geological/constructional problem.

• You- the engineer - must be able to recognize the
  risk or problem
• If you know the problem then you can suggest an
  engineering solution
• If you do not recognize the geological problems
  the engineering construction can be at great risk

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Freedom of choosing the solution

• Political decisions govern
• Existing construct
• Economic restrictions
• Dialogue would be advantageous

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Specific design developed

• design based upon geological conditions
• rock and soil availability for foundations and
  construction materials
• physical properties of the available material
  strength, permeability etc etc

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Investigations for a project

• pre investigations
• maps of all types
• previous reports
• complimentary field studies
• drillings and drill hole logging
• geophysics
• detailed mapping
• active design as the work goes on changes are
  made due to the geological conditions

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Source of maps

• Geological Survey of the country all countries
  have one
• Geological maps of
• bed rock distribution
• soil types and distribution (glacial post
  glacial)
• hydrological conditions
• geophysical (magnetic, electric, radiactivity)
• many other types (engineering, rock quality)

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Methods and scale

• Aerial photo interpretation several are in the
  book for your review
• Field mapping at a scale
• 1/10,000 for highly populated areas
• 1/250,000 for sparsely populated areas
• others -

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Example of the unconsolidated sediments maps 110
000

• Genetic
• Grain Size Sorting
• Mapping depth 50 cm (under soil zone)

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Example of the hydrological maps 110 000

• unconsolidated sediment map (base)
• wells
• location and depth
• production
• chemistry of water
• groundwater table and isochrones
• flow direction

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Example of the bedrock maps 110 000

• rock outcrops identified during soils mapping
• stratigraphic age
• Rock type

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Cross sections of maps

• cross sections
• stratigraphic relationship
• oldest at bottom
• youngest at top
• predicted subsurface continuation of the rocks
  and soils

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Cross sections of maps
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Geological maps of other areas

• Deserts / Non-Glacial areas / Tropics
• How would these differ from those in Sweden?

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Swedens geology

• Precambrian shield (predominately gneiss and
  granite)
• few sedimentary rocks
• extensive hiatus between rocks and unconsolidated
  sediments

• bedrock is covered by
• glacial soils (till, glaciofluvium, glacial clay)
• post glacial soils (post glacial clay, wave
  reworked sand, wind sand, gyttja, peat, alluvium)
• Thickness varies

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Contrast with other countries

• 70 of the earths land area is composed of
  sedimentary rocks
• very few in Sweden

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Contrast with other countries

• Tropics (warm and moist climate) enhances
  chemical weathering
• decomposes the rocks forming soil regolith or
  saprolite overlying the fresh rock, up to 500 m
  deep
• present day Sweden very little chemical
  weathering
• Sweden has been located at the equator thus we
  have remnants of this weathering

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Contrast with other countries

• Non-glaciated areas lack extensive colluvium
  (unconsolidated sediments),
• bedrock outcrops predominate
• alluvium in valleys, thin

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Contrast with other countries

• Desert areas
• sand seas can be extensive
• bedrock usually crops out at surface

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Aerial photos remote sensing -

• satellite images

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Aerial photos remote sensing -

• aerial photos cover all of Sweden
• photos from several different years
• photos of different types
• black white
• infra red
• stereo view

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Aerial photos remote sensing - interpretation

• aerial photos
• satellite photos
• require interpretation and field checking

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Aerial photos remote sensing - interpretation

• slope stability study
• large area viewed in little time
• location of slides mapped
• location compared to geology and geological
  structures
• conclusions can be drawn as to which positions
  along the slope are more susceptible to sliding

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slope failure
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aerial photography

• who does it? Governmental agency!
• you can not order a private study for a given
  project
• photos are available
• you can visit the survey office to view them
• purchase of photos

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aerial photography

• (note that quality varies from year to year so it
  can be good to have visited the office to see
  first that the year you order is not taken when
  there were lots of clouds)

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What can we determine from aerial photos?

• landforms
• landslides
• avalanches
• river meanders (old abandoned channels)
• high water table conditions
• sinkholes

• faults
• volcanic flows extent
• layering of rocks
• strike and dip of rocks
• joints
• magmatic intrusion extent
• alluvial deposits extent

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What can we determine from aerial photos?

• landforms
• landslides
• avalanches
• river meanders (old abandoned channels)
• high water table conditions
• sinkholes

• faults
• volcanic flows extent
• layering of rocks
• strike and dip of rocks
• joints
• magmatic intrusion extent
• alluvial deposits extent

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Map suitability for engineering projects

• Engineering projects are often at a very small
  scale compared to geological maps.
• Geological maps are not to be trusted to show
  the detail that is needed for the project. These
  are constructed to show the geological trends.

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Map suitability for engineering projects

• Example A glacial soils map may show that there
  is a bedrock outcrop in a field of glacial clay.

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WHY???

• The map suggests that the outcrop is 2500 m2
  (1mm2 on the map is the smallest area that can be
  shown on the map at the scale 150,000).
• In reality the outcrop may only be 5m2. But the
  map maker has chosen to include the outcrop
  instead of exclude it from the map.

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information about the depth to bedrock

• What would be the difference with or without
  this outcrop on the map??

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With - without

• With the outcrop we make the interpretation that
  there is not much clay covering the bedrock.
• Without the outcrop we would have interpreted the
  map to indicate that the clay thickness to be
  quite extensive.
• When could this be important??

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Map suitability for engineering projects

• Scale of the geological maps are seldom
  sufficient for engineering projects
• good for a overview and reconnaissance but
• complimenting with detailed mapping is often
  necessary

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Maps are of the surface

• how do we determine the subsurface geology?
• information on maps
• understanding of the stratigraphy
• correct model of the geological history
• Principles of structural geology can be employed
  to predict the extension of the surface geology

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Further investigations!

• trenches and holes

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geophysical methods

• seismic
• electric
• magnetic
• gravity
• radar

• seismic

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geophysical methods

• geophysical methods
• seismic
• electric
• magnetic
• gravity
• radar

• seismic

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seismic in drill holes holes
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geophysical methods

• electric resistivity of electric currents

• geophysical methods
• seismic
• electric
• magnetic
• gravity
• radar

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magnetic

• rocks with different Fe contents

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gravity

• rocks with different densities

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radar

• profile of reflectors
• needs interpetation

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Further investigations!

• logging the cores
• core recovery
• rock quality, RQD
• oriented cores
• index test

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logging the cores

• core recovery
• rock quality, RQD
• oriented cores
• index test

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logging drill holes

• drill holes
• logging drill holes
• heat
• caliper
• geophysical
• water-pressure test
• borehole photography

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logging drill holes

• drill holes
• logging drill holes
• heat
• caliper
• geophysical
• water-pressure test
• borehole photography

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logging drill holes

• drill holes
• logging drill holes
• heat
• caliper
• geophysical
• water-pressure test
• borehole photography

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logging drill holes

• drill holes
• logging drill holes
• heat
• caliper
• geophysical
• water-pressure test
• borehole photography

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trenches

• a scratch at the surface

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Further investigations!

• trenches
• geophysics
• drilling
• logging drill holes
• logging cores

• Complimentary tests are expensive
• students seem to believe geophysics is the answer
  to everything
• NO
• Interpretation is needed

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Further investigations!

• Maps are relatively inexpensive
• Complimentary tests are costly

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Further investigations!

• Maps are relatively inexpensive
• Complimentary tests are costly

• drill holes are isolated points

• geophysic profiles one line

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What information do we get from maps compared to
complimentary tests?

• amount of information
• accuracy of information
• cost of obtaining information
• cost of having to change our project if the
  geology is unsuitable for the design

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What information do we get from maps compared to
complimentary tests?

• maps
• Principles of Structural geology can be employed
  to predict the subsurface extension of the
  surface geology

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What information do we get from maps compared to
complimentary tests?

• geophysics
• can be applied to areas or linear traverses.
  They, however, require interpretation, which in
  turn requires concrete information from drill
  holes

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What information do we get from maps compared to
complimentary tests?

• drill holes
• isolated points that show the relationships
  downward at that point
• information from the drilling is not 100 exact
• what comes up is often bits and pieces of rock

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Important questions

• where do we need to know more about the
  subsurface geology
• what geophysical methods can be used
• where, how frequent, do we need to drill
• what is our budget
• what is the required level need for the project

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what is the required level need for the project

• Dignity of the engineering project dictates the
  need for pre-investigations
• coupled to
• construction cost
• risk due to failure
• EXAMPLES?

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dignity of engineering projects

• Sport area for running, football etc
• Private home
• Road / Railroad construction
• High-rise housing project
• Rock quarry or gravel pit
• Dam
• Land fill
• Mine
• Tunnels
• Construction of an atomic energy plant

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dignity of engineering projects

• Would there be any general difference for
  pre-investigations required in Sweden compared to
  other countries?
• Past results
• tradition

• Geological situation in Sweden
• Geological situation in another country

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Geological processesCharacter of rock mass

• Sweden
• no large earthquakes
• last volcanic eruption was millions of years ago
• landslides occur
• floods occur
• hard crystalline rocks predominate

• Other countries

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Data base

• basis for decisions concerning pre-investigations

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correctness of pre- investigations

• pre-investigations are the basis for bids
• project commissioned
• operation and maintenance phase
• geology evaluated real compared to predicted

• interactive construction
• real geological conditions documented
• evaluation of design versus the real conditions
• possible change in design
• information concerning the geology needs to be
  added to the data base so future projects can
  gain