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
Kaolinite structure
- 1:1 silica:octahedron - sheets are stacked forming aggregates - hexagonal flakes - common in sedimentary and residual soils - pottery clay - low activity
26
Illite structure
- 2:1 silica:octahedral - octahedral sandwiched between 2 silica sheets - potassium between layers - most common in engineering
27
Bentonite structure
- 2:1 silica:octahedral - octahedral sandwiched between 2 silica sheets - water between layers
28
how do volcanic clays differ?
not organised in sheets and have unique behaviour
29
________ identified by greasy feel when soil worked between thumb and forefinger. ______ can be weathering product of this.
Allophane, Halloysite
30
soil fabric structure
Fabric + composition + inter particle forces
31
describe what is meant by soil fabric
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
cohesionless soils
forces between particles are due to friction
33
cohesive soils
forces arise from electric repulsion through absorbed water layer between clay particles
34
first step in soil classification. What do you use?
determine grain size. | using a sieve if coarse, or for fine grains use hydrometer analysis
35
sedimentation analysis / hydrometer analysis, uses which law?
Stoke's Law
36
void ratio
ratio of volume of voids : volume of solid particles
37
relative density
measure of how densely the grains are packed in a coarse soil
38
clay goes from solid - semi solid - plastic - liquid, as what increases?
water content
39
Atterberg limits concern what?
soil plasticity
40
liquid limit
water content at the boundary of liquid - plastic
41
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
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
The liquid limit for sedimentary soils is not sensitive to wetting and drying. TRUE/FALSE
TRUE
43
soils containing ________ are very sensitive to cycles of wetting and drying
allophane
44
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.
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
Plastic limit
moisture content at which a thread os soil just begins to crack and crumble when rolled to a diameter of 3mm
46
Plasticity index =
= liquid limit - plastic limit. | range in which soil behaves plastically
47
liquidity index is a useful indicator of what?
state of soil. LI > than 1 = sensitive soil. w > LL = soft / low strength soil w ~ PL = strong soil
48
``` USCS symbols for: GRAVEL: SAND: SILT: CLAY: ORGANIC: PEAT: ```
``` USCS symbols for: GRAVEL: G SAND: S SILT: M CLAY: C ORGANIC: O PEAT: Pt ```
49
what would SC, SW and MH stand for?
``` SC = clayey sand SW = graded sand MH = elastic silt ```
50
On the Plasticity chart, The A-line seperates? | The U-line indicates?
A- line seperates clay from silt, and organics from inorganics. U-line indicates upper bound for general soils.