engineer and engineering geologist what should you be able to do as an engineer who works together...

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

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?

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!!

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)

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

Freedom of “choosing” the solution

• Political decisions govern

• Existing construct

• Economic restrictions

• Dialogue would be advantageous

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

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

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)

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 -

Example of the unconsolidated sediments maps 1:10 000

• Genetic• Grain Size & Sorting

• Mapping depth 50 cm (under soil zone)

Example of the hydrological maps 1:10 000

• unconsolidated sediment map (base)

• wells– location and depth– production– chemistry of water

• groundwater table and isochrones

• flow direction

Example of the bedrock maps

1:10 000

• rock outcrops identified during “soils” mapping

• stratigraphic age• Rock type

Cross sections of maps

• cross sections – stratigraphic

relationship

• oldest at bottom

• youngest at top

– predicted subsurface continuation of the rocks and soils

Cross sections of maps

Geological maps of other areas

Deserts / Non-Glacial areas / Tropics

How would these differ from those in Sweden?

Sweden’s 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

Contrast with other countries

• 70% of the earth’s land area is composed of sedimentary rocks– very few in Sweden

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


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


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

Aerial photos – remote sensing -

• satellite images

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

Aerial photos – remote sensing - interpretation

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

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

slope failure

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

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)

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

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.


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

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 1:50,000).

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.

information about the depth to bedrock

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

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??


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

Maps are of the surface

- how do we determine the subsurface geology?

- information on maps- understanding of the stratigraphy- correct model of the geological historyPrinciples of structural geology can be

employed to predict the extension of the surface geology

Further investigations!

trenches and holes

geophysical methods

- seismic

- electric

- magnetic

- gravity

- radar

– seismic

geophysical methods

geophysical methods- seismic

- electric

- magnetic

- gravity

- radar

– seismic

seismic in drill holes holes

geophysical methods

geophysical methods- seismic

- electric

- magnetic

- gravity

- radar

electric – resistivity of electric currents

magnetic

• rocks with different Fe contents

gravity

• rocks with different densities

radar

• profile of reflectors• needs interpetation


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

logging the cores

core recovery rock quality, RQD oriented cores index test

logging drill holes

• drill holes• logging drill holes

heat caliper geophysical water-pressure test borehole photography

trenches

• a scratch at the surface


- 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


- Maps are relatively inexpensive

- Complimentary tests are costly


- Maps are relatively inexpensive

- Complimentary tests are costly

•geophysic profiles = one line

•drill holes are isolated points

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


tests?

• maps

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


tests?

• geophysics

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


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

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

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?

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

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

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

“Data base”

• basis for decisions concerning pre-investigations

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

engineer and engineering geologist what should you be able to do as an engineer who works together...

Documents

advantageous slide

rock quality slide

geological conditions

engineering solution

engineering geologist

subsurface geology slide

great risk slide

hydrological maps