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ENCN253 > Module 5 Review Questions > Flashcards

Module 5 Review Questions Flashcards

1
Q

What activities provide information for a ground profile

A
  • soil geology
  • site investigation
  • soil description
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2
Q

Define the discipline of engineering geology

A

The application of geological sciences to engineering practice

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3
Q

Investigations commonly performed by an engineering geologist

A
  • geological hazards
  • geotech and material properties
  • landslide and slope stability
  • erosion, flooding dewatering
  • seimsic hazards
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4
Q

what is the greatest impediment to obtaining soils information

A

access to subsurface is limited and soil samples are usually collected from a very limited number of locations and are generally disturbed

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5
Q

Under what conditions does engineering on slopes become problematic

A

all slopes have potential to be problematic, but conditions of increased pore pressure (reduced effective stress) generally promote slope instability

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6
Q

what aspect of the ground is most important when considering the stability of slopes

A

groundwater (pore pressure)

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7
Q

what aspects of the ground are important to consider when selecting a dam site

A
  • strength and stability of abutments

- dam footprint and its permeability

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8
Q

what aspects of the ground are most important for foundation design of a multi-storing building

A

bearing capacity of soils and rocks within the building footprint

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9
Q

why do deep excavations require consideration of the groundwater regime

A
  • base of excavation may be beneath groundwater table

- risk of flooding or base heave due to high pore pressure

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10
Q

what aspects of river flood plain soils give rise to common geotechnical problems

A
  • high water content and presence of organic soils both give rise to large settlements upon loading
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11
Q

what measurements can be taken to improve the tensile strength of soils in earth embankments

A
  • soil mixing with the addition of ‘binder’ material (cement)
  • placement of tensile geogrid layers between ‘lifts’ of soil
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12
Q

why are tunnel portals often areas of significant engineering problems

A

located on slopes in near surface materials that have been subject to weathering and stress relief
- therefore weaker than expected and give rise to slope instability

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13
Q

Why do geologically recent glacial periods control the soils in shallow marine environments

A

recent glaciations responsible for a drop in global sea level
- exposed much of shallow marine environment to subaerial processes which dominate soil found in these areas

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14
Q

What are the difference between natural, in situ soils and the soil samples commonly tested in the laboratory

A
  • natural, in situ soils are undisturbed

- in most lab tested soils the material has been homogenised to remove the effects of structure and bonding

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15
Q

Two common human activities that lead to ground subsidence

A
  • intensive agriculture
  • mining
  • tunneling
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16
Q

What type of dam would you construct in a region of suspected surface fault rupture hazard

A

embankment dam

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17
Q

What rock cycle processes lead to the formation of soil

A
  • weathering
  • transportation
  • deposition
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18
Q

What soils are found in the region in and around Christchurch

A
  • Loess
  • alluvium
  • peat
  • silts sands and gravels
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19
Q

What generally controls the strength of a sedimentary rock

A

the cemented material

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20
Q

Of the three main rock types, which would you expect to have the greatest permeability

A

Sedimentary

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21
Q

What are the three main chemical reaction processes involved in chemical weathering

A
  1. oxidation
  2. hydrolysis
  3. dissolution
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22
Q

What are the common products of chemical weathering of crystalline rocks

A
  • clay
  • potassium ion
  • bicarbonate ion
  • silica
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23
Q

Why is the rockhead (boundary between unweathered rock and overlying residual soil) irregular under conditions of chemical weathering

A
  • permeability of the rock

- spacing of discontinuities

24
Q

What controls the rate of chemical weathering

A
  • original rocks
  • climate
  • surface area
25
Q

what are some of the common engineering problems in karst terrain

A

limestone

  • caves
  • lead to sinkholes
26
Q

what rocks commonly contain pyrite

A

coal and shale deposits

27
Q

Describe the nature of the contact between rock and residual soil

A

rockhead

28
Q

What are the common effects of liquefaction on foundations

A
  • loss of bearing capacity
  • loss of frictional strength
  • differential settlement
29
Q

What conditions give rise to the majority of debris flow

A

heavy rainfall on colluvial slopes

30
Q

which soils exhibit expansive behaviour

A

mixed-layer clays

31
Q

Name three common causes of ground subsidence

A
  • natural cavern collapse
  • mining-induced or tunneling-induced settlement
  • tectonic movement
  • dewatering
32
Q

Erosion is common in what geological environments

A

ALLL - anywhere where there is sufficient energy to transport loose, non-bonded gemoaterial

33
Q

As well as case histories what improves our general understanding of soil behaviour in geotechnical engineering

A

experience

34
Q

Name and describe the effects of three agents of erosion

A
  1. Water - transport soils of differing grain sizes along the course of a river
  2. Wind - transport of soils of a limited grain size (sand or smaller)
  3. Ice- glacial transport of soils - grinding bedrock to produce rock flour
35
Q

What measures can be taken to mitigate the hazards with slope instability

A
  1. Drainage
  2. Slope Grading
  3. Improve slope materials
  4. Anchoring
36
Q

What type of dam would you construct in a region of suspected surface fault rupture hazard?

A

zoned earth embankment

  • sufficient freeboard to accommodate vertical displacement
  • large clay core and filters (to accommodate fault movement without complete dislocation)
37
Q

What mitigation measures would you reccommend for an area subject to episodic debris flow activity

A
  • AVOIDANCE
  • debris dams and levees
  • controlled slope drainage
38
Q

what common soil type is prone to internal erosion

A

loess

39
Q

What physical characteristics control the overall mechanical behaviour of rock?

A

Discontinuities (fractures, joints, faults)

40
Q

What physical characteristic control the overall mechanical behaviour of the soil

A

grain size and geometry

41
Q

Differences between oceanic and continental crust

A

Oceanic - thin, dense, composed of basic igneous rock (basalt)
Continental - thick, less dense, composed of acidic igneous rock (granite)

42
Q

What geological time period is of most importance for engineering

A

the most recent - Quaternary era

43
Q

What are the prominent Quaternary soil types in NZ

A
  • loess
  • alluvial
  • volcanic ash
  • glacial
44
Q

Differences between intrusive and extrusive rocks

A
  • extrusive = rapid cooling, fine crystals

- intrusive = slow cooling, coarse crystals

45
Q

Differences between acidic and basic igneous rocks

A
  • acidic contain free silica

- colour

46
Q

Would metamorphic rocks make a good aggregate source? Why?

A

No
- alignment of crystals means that when crushed, metamorphic rock tends to have tabular shape, leading to strongly anisotropic strength when the particles align

47
Q

Bedrock in South Island?

A

Greywacke (sedimentary rock = mostly sandstone)

48
Q

Where would you expect thermal expansion to occur as a weathering process

A

anywhere where there is a high diurnal temperature range e.g. high altitude desert areas

49
Q

What are the three main chemical reaction proccesses involved in chemical weathering

A
  • Hydrolysis
  • Dissolution
  • Oxidation
50
Q

What rocks are most susceptible to chemical weathering

A
  • high temperature (basic) igneous rocks and soluble sedimentary rocks
51
Q

what are the common products of chemical weathering of crystalline rocks

A

clays

52
Q

what soil would result from complete chemical weathering of granite

A

clay-rich soil containing quartz grains (sand to gravel size)

53
Q

what controls rate of chemical weathering

A

rock composition, climate and surface area

54
Q

what is the result of chemical weathering of limestone

A

Karst terrain (caves etc.)

55
Q

What measures would you take to minimise the impact of pyrite on foundations

A

prevent exposure to atmosphere or remove all pyrite-containing materials

56
Q

What influences the structure of residual soils?

A

the parent rock

57
Q

what is the most common terrestrial soil transport mechanism?

A

rivers (fluvial environment)

ENCN253 (6 decks)

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