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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.

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Presentation on theme: "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."— Presentation transcript:

1 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

2 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?

3 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!!

4 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)

5 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

6 Freedom of “choosing” the solution Political decisions govern Existing construct Economic restrictions Dialogue would be advantageous

7 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

8 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

9 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)

10 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 -

11 Example of the unconsolidated sediments maps 1: Genetic Grain Size & Sorting Mapping depth 50 cm (under soil zone)

12 Example of the hydrological maps 1: unconsolidated sediment map (base) wells –location and depth –production –chemistry of water groundwater table and isochrones flow direction

13 Example of the bedrock maps 1: rock outcrops identified during “soils” mapping stratigraphic age Rock type

14 Cross sections of maps cross sections –stratigraphic relationship oldest at bottom youngest at top –predicted subsurface continuation of the rocks and soils

15 Cross sections of maps

16 Geological maps of other areas Deserts / Non-Glacial areas / Tropics How would these differ from those in Sweden?

17 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

18 Contrast with other countries 70% of the earth’s land area is composed of sedimentary rocks –very few in Sweden

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20 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

21 Contrast with other countries Non-glaciated areas lack extensive colluvium (unconsolidated sediments), – bedrock outcrops predominate –alluvium in valleys, thin

22 Contrast with other countries Desert areas –sand seas can be extensive –bedrock usually crops out at surface

23 Aerial photos – remote sensing - satellite images

24 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

25 Aerial photos – remote sensing - interpretation aerial photos satellite photos require interpretation and field checking

26 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

27 slope failure

28 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

29 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)

30 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

31 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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36 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.

37 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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39 WHY??? The map suggests that the outcrop is 2500 m 2 (1mm 2 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 5m 2. But the map maker has chosen to include the outcrop instead of exclude it from the map.

40 information about the depth to bedrock What would be the difference with – or without this outcrop on the map??

41 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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43 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

44 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

45 Further investigations!  trenches and holes

46 geophysical methods -seismic -electric -magnetic -gravity -radar –seismic

47 geophysical methods  geophysical methods -seismic -electric -magnetic -gravity -radar –seismic

48 seismic in drill holes holes

49 geophysical methods  geophysical methods -seismic -electric -magnetic -gravity -radar electric – resistivity of electric currents

50 magnetic rocks with different Fe contents

51 gravity rocks with different densities

52 radar profile of reflectors needs interpetation

53 Further investigations!  logging the cores  core recovery  rock quality, RQD  oriented cores  index test

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

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

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

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

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

59 trenches a scratch at the surface

60 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

61 Further investigations! -Maps are relatively inexpensive -Complimentary tests are costly

62 Further investigations! -Maps are relatively inexpensive -Complimentary tests are costly geophysic profiles = one line drill holes are isolated points

63 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

64 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

65 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

66 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

67 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

68 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?

69 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

70 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

71 Geological processes Character 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

72 “Data base” basis for decisions concerning pre- investigations

73 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


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