Soil

Question 1

Soil vs. Rock similarities

Answer 1

both are natural aggregate of mineral grains

Question 2

Soil vs Rock differences

Answer 2

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

Question 3

Soils are products of….?

Answer 3

rock weathering

Question 4

gravel =

sand =

silt =

clay =

Answer 4

• 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

Question 5

why is soil called a 3-phase material?

Answer 5

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

Question 6

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

Answer 6

NO

Question 7

does soil exhibit linear plastic behaviour?

Answer 7

NO, non-linear

Question 8

Soil is anisotropic and heterogenous, what does that mean?

Answer 8

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

Question 9

geotechnical challenges of soil

Answer 9

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

Question 10

residual vs transported soil

Answer 10

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

Question 11

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

Answer 11

hilly and mountainous areas.

Question 12

flat low-lying areas produce what type of soils?

Answer 12

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

Question 13

Aeolian, fluvial and glacial soils

Answer 13

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

Question 14

volcanic soils

Answer 14

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

Question 15

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

Answer 15

homogeneous deposits

Question 16

residual soils formation

Answer 16

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

Question 17

Auckland clays are a common example of?

Answer 17

residual soil

Question 18

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

Answer 18

transported

Question 19

would angular sand grains or round sand grains be stronger?

Answer 19

angular, because they can interlock

Question 20

what dominates the behaviour of clay ?

Answer 20

water interaction

Question 21

why is clay so problematic?

Answer 21

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

Question 22

is clay hydrophilic or hydrophobic?

Answer 22

hydrophilic

Question 23

2 clay mineral building blocks

Answer 23

1. Silicon tetrahedron

2. Alumina Octahedron

Question 24

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

Answer 24

1. Kaolinite
2. Illite
3. Bentonite

Question 25

Kaolinite structure

Answer 25

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

Question 26

Illite structure

Answer 26

- 2:1 silica:octahedral - octahedral sandwiched between 2 silica sheets - potassium between layers - most common in engineering

Question 27

Bentonite structure

Answer 27

- 2:1 silica:octahedral - octahedral sandwiched between 2 silica sheets - water between layers

Question 28

how do volcanic clays differ?

Answer 28

not organised in sheets and have unique behaviour

Question 29

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

Answer 29

Allophane, Halloysite

Question 30

soil fabric structure

Answer 30

Fabric + composition + inter particle forces

Question 31

describe what is meant by soil fabric

Answer 31

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.

Question 32

cohesionless soils

Answer 32

forces between particles are due to friction

Question 33

cohesive soils

Answer 33

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

Question 34

first step in soil classification. What do you use?

Answer 34

determine grain size. | using a sieve if coarse, or for fine grains use hydrometer analysis

Question 35

sedimentation analysis / hydrometer analysis, uses which law?

Answer 35

Stoke's Law

Question 36

void ratio

Answer 36

ratio of volume of voids : volume of solid particles

Question 37

relative density

Answer 37

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

Question 38

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

Answer 38

water content

Question 39

Atterberg limits concern what?

Answer 39

soil plasticity

Question 40

liquid limit

Answer 40

water content at the boundary of liquid - plastic

Question 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

Answer 41

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

Question 42

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

Answer 42

TRUE

Question 43

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

Answer 43

allophane

Question 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.

Answer 44

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.

Question 45

Plastic limit

Answer 45

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

Question 46

Plasticity index =

Answer 46

= liquid limit - plastic limit. | range in which soil behaves plastically

Question 47

liquidity index is a useful indicator of what?

Answer 47

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

Question 48

``` USCS symbols for: GRAVEL: SAND: SILT: CLAY: ORGANIC: PEAT: ```

Answer 48

``` USCS symbols for: GRAVEL: G SAND: S SILT: M CLAY: C ORGANIC: O PEAT: Pt ```

Question 49

what would SC, SW and MH stand for?

Answer 49

``` SC = clayey sand SW = graded sand MH = elastic silt ```

Question 50

On the Plasticity chart, The A-line seperates? | The U-line indicates?

Answer 50

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