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CIVIL two twenty > Soil > Flashcards

Soil Flashcards

1
Q

Soil vs. Rock similarities

A

both are natural aggregate of mineral grains

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2
Q

Soil vs Rock differences

A
  • soil aggregates can be separated by mechanical means (agitation in water)
  • Rock aggregate minerals are connected by stronger forces
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3
Q

Soils are products of….?

A

rock weathering

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4
Q

gravel =

sand =

silt =

clay =

A
  • gravel = small rocks
    with a mix of minerals.
  • sand = small grains of a SINGLE mineral
  • silt = same but grains not visible to naked eye
  • clay = tiny plate-like minerals
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5
Q

why is soil called a 3-phase material?

A

solid - soil grains
liquid - usually water
gas - usually air

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6
Q

soil is a frictional material. Does it have tensile strength?

A

NO

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7
Q

does soil exhibit linear plastic behaviour?

A

NO, non-linear

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8
Q

Soil is anisotropic and heterogenous, what does that mean?

A

huge range of properties. Every soil is different, different in each location and huge variety

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9
Q

geotechnical challenges of soil

A
  1. settlement
  2. strength (bearing capacity and slope stability
  3. seepage
  4. liquefaction
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10
Q

residual vs transported soil

A

residual is a product of rock weathering and remains in place, transported is taken to other locations

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11
Q

where would you find clay minerals with good drainage and soils with good engineering properties?

A

hilly and mountainous areas.

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12
Q

flat low-lying areas produce what type of soils?

A

poor drainage with little or no vertical seepage. Bad engineering properties

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13
Q

Aeolian, fluvial and glacial soils

A

aeolian transported by wind, fluvial rivers/streams, glacial glaciers

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14
Q

volcanic soils

A
  • layers represent seperate volcanic events
  • high water content
  • ash soils tend to drain quickly (no puddles)
  • often sensitive
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15
Q

sorting process of transported soils, leads to more __________ deposits (especially fluvial and aeolian)

A

homogeneous deposits

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16
Q

residual soils formation

A

formed by growth and decay of plants (peat, mosses) or accumulation of fragments of inorganic skeletons or shells

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17
Q

Auckland clays are a common example of?

A

residual soil

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18
Q

traditional soil mechanics is based on the properties of which soil type?

A

transported

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19
Q

would angular sand grains or round sand grains be stronger?

A

angular, because they can interlock

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20
Q

what dominates the behaviour of clay ?

A

water interaction

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21
Q

why is clay so problematic?

A

small amounts can dominate overall behaviour of soil. Clay has low strength, swells, is highly compressible, and has low hydraulic conductivity

22
Q

is clay hydrophilic or hydrophobic?

A

hydrophilic

23
Q

2 clay mineral building blocks

A
  1. Silicon tetrahedron

2. Alumina Octahedron

24
Q

3 common clay minerals in increasing activity and decreasing order of stacking

A
  1. Kaolinite
  2. Illite
  3. Bentonite
25
Q

Kaolinite structure

A
  • 1:1 silica:octahedron
  • sheets are stacked forming aggregates
  • hexagonal flakes
  • common in sedimentary and residual soils
  • pottery clay
  • low activity
26
Q

Illite structure

A
  • 2:1 silica:octahedral
  • octahedral sandwiched between 2 silica sheets
  • potassium between layers
  • most common in engineering
27
Q

Bentonite structure

A
  • 2:1 silica:octahedral
  • octahedral sandwiched between 2 silica sheets
  • water between layers
28
Q

how do volcanic clays differ?

A

not organised in sheets and have unique behaviour

29
Q

________ identified by greasy feel when soil worked between thumb and forefinger. ______ can be weathering product of this.

A

Allophane, Halloysite

30
Q

soil fabric structure

A

Fabric + composition + inter particle forces

31
Q

describe what is meant by soil fabric

A

the arrangement of particles. Elementary mineral units tend to settle individually in quiet water. Sediments become more anisotropic. Platy/ elongated particles tend to rotate into horizontal positions.

32
Q

cohesionless soils

A

forces between particles are due to friction

33
Q

cohesive soils

A

forces arise from electric repulsion through absorbed water layer between clay particles

34
Q

first step in soil classification. What do you use?

A

determine grain size.

using a sieve if coarse, or for fine grains use hydrometer analysis

35
Q

sedimentation analysis / hydrometer analysis, uses which law?

A

Stoke’s Law

36
Q

void ratio

A

ratio of volume of voids : volume of solid particles

37
Q

relative density

A

measure of how densely the grains are packed in a coarse soil

38
Q

clay goes from solid - semi solid - plastic - liquid, as what increases?

A

water content

39
Q

Atterberg limits concern what?

A

soil plasticity

40
Q

liquid limit

A

water content at the boundary of liquid - plastic

41
Q

Casagrande Apparatus. The moisture content at which a _ mm-wide groove in a soil pat will close for a distance of 13 mm when dropped __ times in a standard brass cup falling _ cm each time at a rate of 2 drops/sec in a standard liquid limit device

A

Casagrande Apparatus. The moisture content at which a 2 mm-wide groove in a soil pat will close for a distance of 13 mm when dropped 25 times in a standard brass cup falling 1 cm each time at a rate of 2 drops/sec in a standard liquid limit device

42
Q

The liquid limit for sedimentary soils is not sensitive to wetting and drying. TRUE/FALSE

A

TRUE

43
Q

soils containing ________ are very sensitive to cycles of wetting and drying

A

allophane

44
Q

liquid limit cone penetrometer. The liquid limit of the soil is the moisture content at which an __ g, __ degree cone sinks exactly __ mm into a cup of remoulded soil in a 5s period.

A

liquid limit cone penetrometer. The liquid limit of the soil is the moisture content at which an 80 g, 30 degree cone sinks exactly 20 mm into a cup of remoulded soil in a 5s period.

45
Q

Plastic limit

A

moisture content at which a thread os soil just begins to crack and crumble when rolled to a diameter of 3mm

46
Q

Plasticity index =

A

= liquid limit - plastic limit.

range in which soil behaves plastically

47
Q

liquidity index is a useful indicator of what?

A

state of soil.
LI > than 1 = sensitive soil.
w > LL = soft / low strength soil
w ~ PL = strong soil

48
Q 
USCS symbols for:
GRAVEL:
SAND:
SILT:
CLAY:
ORGANIC:
PEAT:
A 
USCS symbols for:
GRAVEL: G
SAND: S
SILT: M
CLAY: C
ORGANIC: O
PEAT: Pt
49
Q

what would SC, SW and MH stand for?

A 
SC = clayey sand
SW = graded sand
MH = elastic silt
50
Q

On the Plasticity chart, The A-line seperates?

The U-line indicates?

A

A- line seperates clay from silt, and organics from inorganics.
U-line indicates upper bound for general soils.

CIVIL two twenty (16 decks)

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