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ENCN253 > MODULE 5 > Flashcards

MODULE 5 Flashcards

1
Q

Soil Mechanics Triangle

A
  • Ground Profile
  • Appropriate Model
  • Soil Behaviour
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2
Q

Types of Ground Failure

A
  • volcanic eruptions
  • earthquakes and liquefaction
  • landslides
  • expansive soils
  • subsidence
  • erosion (and deposition)
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3
Q

Volcanic Hazards engineering

A
  • generally not a surprise
  • active volcanic sites known and monitored
  • engineered solutions expensive and dont always work so best mitigation is avoidance
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4
Q

Volcanic Hazards

A
  • noxious gases, floods, tsunami, atmospheric shock waves

- crop damage, livestock poisoning, water contamination, famine

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5
Q

Earthquake Hazards

A
  • little knowledge of earthquake effects (learning constantly)
  • effects can be mitigated by engineering design, however not always economic
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6
Q

Liquefaction Requirements

A
  • strong earthquake motion
  • loose, granular soil
  • shallow groundwater
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7
Q

3 Layers of Earth

A
  • core (inner and outer)
  • mantle
  • crust
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8
Q

lithosphere

A

continental crust - thicker but less dense
oceanic crust - thinner and more dense
- where it all happens

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9
Q

Plate Movement

A
  • Divergent Boundary
  • Convergent Boundary
  • Transform Boundary
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10
Q

Divergent Boundary

A

plates move away from each other - small earthquakes

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11
Q

Convergent Boundary

A

plates forced together and under each other - large earthquakes (North and South Islands)

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12
Q

Transform Boundary

A

plates slide past each other (central New Zealand)

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13
Q

New Zealand Plates

A

North: Pacific under Australian
South: Australian under Pacific
Centre: transform fault to account for differences

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14
Q

Geological Processes of Christchurch

A
  • glaciers, rivers, sea, volcanoes, earthquakes
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15
Q

Basic Rock Types

A
  • igneous
  • metamorphic
  • sedimentary
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16
Q

Igneous

A
  • crystals
  • isotropic (randomly arranged)
  • strong
  • good aggregate
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17
Q

Metamorphic

A
  • crystals
  • anisotropic (aligned)
  • variable strength
  • poor aggregate
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18
Q

Sedimentary

A
  • particles
  • anisotropic (macro scale)
  • isotropic (micro scale)
  • variable strength
  • variable aggregate quality
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19
Q

extrusive

A

cools quickly (fine crystals)

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20
Q

intrusive

A

cools slowly (coarse crystals)

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21
Q

basic

A

dark colour

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22
Q

acidic

A

lighter colour

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23
Q

increasing metamorphism

A
  • rock becomes increasingly crystalline
  • crystals become larger
  • crystals align
  • eventually different minerals segregate into bands
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24
Q

Earth’s External Processes

A
  • Weathering
  • Erosion
  • Mass Wasting
25
Q

Erosion

A

physical removal of material by mobile agents such as water, wind, ice or gravity

26
Q

Mass Wasting

A

transfer of rock and soil downslope under the influence of gravity

27
Q

Weathering

A
  1. Physical Weathering - breaking of rocks into smaller pieces without changing their composition
  2. Chemical Weathering - breaks down rock components and changes its mineral and chemical composition
28
Q

Types of Physical Weathering

A
  • frost wedging
  • unloading
  • thermal expansion
  • biological activity
29
Q

Weathering Susceptibility

A
  • original rocks
  • dry climate (cold or hot) likely to experience mechanical weathering
  • wet climate (especially hot) likely to experience chemical weathering (fast) - cold temps = slower
  • surface area, fracture density
30
Q

Residual Soil

A

(in situ)

- forms in place on bedrock, no input of outside material

31
Q

Transported Soil

A
  • forms an unconsolidated material transported to site (not local bedrock)
32
Q

Weathering of Pyrite

A
  • very reactive in O2
  • frequently formed in coal and shale deposits
  • oxidation leads to volume increase and pyrite heave
33
Q

Mitigation for Pyrite Heave

A
  • excavate with minimum disturbance to rock (shattering of bedrock provides easy entry of air)
  • protect exposed surfaces with concrete grout or asphalt coating
  • insulate basement floor
  • avoid building on fractured shale
  • avoid use of pyritic material as fill
  • removal of pyrite fill
34
Q

Transportation agents

A
  • water (fluvial = river ; marine = sea)
  • ice (glacial)
  • wind
  • gravity
35
Q

with increasing transport distance:

A
  • particles become smaller
  • particles become more rounded (spherical)
  • particle size distribution becomes more uniform (poorly graded)
36
Q

Soil characteristics determined by:

A
  • source material
  • transport mechanism
  • transport distance
  • energy of system
  • depositional environment
37
Q

Peat

A
  • high water content
  • low bearing capacity
  • low shear strength
  • highly compressible
  • oxidise
  • flammable
38
Q

avulsion

A

sudden change of channel position

39
Q

braided river

A
  • multiple streams (braids) divided by bars composed of either sand or gravel
  • often extremely dynamic (bars may change position on a day to day basis)
40
Q

Problems with Braided Rivers

A
  • bank erosion
  • loss of land
  • bridge destabilisation
  • flooding
41
Q

Major hazards in fluvial soils

A
  • peat
  • scour
  • channel migration
42
Q

Engineering Hazards (glacial soil)

A
  • Loess: collapsible, high permeability and subject to internal corrosion
  • Varved clays (marine): sensitive and prone to liquefaction and flow
43
Q

glaciofluvial deposits

A

sediments formed in association with glacial meltwater

44
Q

varved clays

A

fine grained in cold months ; coarse grained in warm months

- form layers ; hazard from spontaneous liquefaction (high w/c, low strength)

45
Q

Ice Transport

A
  • ice flows as a result of gravity (laminar flow)
  • transport distance does NOT increase roundness or decrease grain size
  • can transport very large grains (>10 m)
  • grinding at base of (warm) ice produces rock flour
46
Q

abrasion

A

ice flowing over rock/soil, grinding it smaller and smaller

  • leads to formation of rock flour
  • can open rock fractures
  • warm-based ice tends to be more erosive or abrasive
47
Q

Till

A

glacial deposit that is angular and gap-graded

48
Q

Marine environment - nearshore/shallow water

A

highest energy, coarse material

49
Q

Marine environment - wave dominated shorelines

A

high energy, sand and gravel

50
Q

Marine environment - estuaries and lagoons

A

low energy, silt and clay

51
Q

Marine environment - red/dead seas

A

lowest energy, evaporation and deposition of salts

52
Q

Deep Sea sedimentation - Slumps

A

sediment transport by mass with little deformation or folding of layers

53
Q

Deep Sea sedimentation - Slurries

A

debris flows and mud flows, destroy any previous bedding layer

  • turbidity currents
  • deep sea canyons form by these processes
54
Q

Deep Sea sedimentation - Ice Rafting

A
  • polar latitudes, debris melting from icebergs

- glacial marine sediment

55
Q

Turbidity Currents

A
  • slopes above 2o considered relatively steep and worried about slips/failure and stability
  • tends to be channelised flow
  • as gradient decreases, sediment begins to deposit
  • turbidites: what remains after deposition from turbidity currents (well stratified according to grain size)
56
Q

Mass Wasting

A
  • all processes that bring about slow or rapid downslope movement of soil and rock as a result of gravity
  • due to slope angle, slope position and amount of water
  • occurs when shear stress is greater than shear strength
57
Q

Classification of Landslides

A
  1. Falls - immediate separation of falling material from parent rock or soil mass
  2. Slide - moving material remains in contact and movement takes place along discrete shear surfaces
  3. Flows - material becomes disaggregated and movement occurs without necessarily forming discrete shear surfaces
58
Q

Landslide Stabilization

A
  1. Drainage
  2. Improving Slope Material
  3. Modifying Slope Profile
  4. Supporting or Anchoring the Slide Mass

ENCN253 (6 decks)

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