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CE431 Engineering geology and soil mechanics > Topic 2: Fine soil classification > Flashcards

Topic 2: Fine soil classification Flashcards

1
Q

What soils are classed as ‘fine soils’?

A

Clay and Silt.

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2
Q

What are the three main properties of clay?

A
  • Extremely flaky shape
  • Small particle size
  • Negative electrical charge on surface
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3
Q

Finish the statement:’ The smaller and flakier a particle is, the _______ will be its _______ ____.

A

(1) greater
(2) surface
(3) area

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4
Q

What is the symbol for Specific Surface?

A

S subscript s.

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5
Q

What is the equation for specific surface?

A

Specific surface = surface area (m^2)/ mass (g)

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6
Q

What is the specific surface equation for a 6-sided cube?

A

Specific surface of cube = 0.006/length x density of cube

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7
Q

What is the highest value for the specific surface of clay?

A

up to 350 m^2g^-1

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8
Q

Under what category of minerals does clay fall under?

A

Silicates, the most common group of minerals.

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9
Q

What do all silicates have in common?

A

They all contain the SiO4 tetrahedron.

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10
Q

What does a silicate tetrahedron contain?

A

It contains one Si4+ at the centre and four oxygen ions O^-2 at the corners.

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11
Q

What does a tetrahedral sheet consist of?

A

Multiple tetrahedrons placed next to each other.

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12
Q

What does a Octahedron consist of?

A

1 Aluminium/Magnesium ion surrounded by 6 oxygen ions.

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13
Q

Why do sheet silicates form flaky particles?

A

Weak bonds exist between the sheets where no oxygen ions are shared (lack of ionic bonding).

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14
Q

What does a 1:1 structure (Kaolin) consist of?

A

1 tetrahedron and one octahedron sheet.

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15
Q

How are the the tetrahedron sheet and octahedron sheet bonded?

A

By the strong bonds of shared oxygen-ions.

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16
Q

What does a 1:2 structure (TOT) consist of?

A

One octahedron sheet sandwiched between two tetrahedron sheets.

17
Q

What is the process of clay swelling?

A

Water enters the space between the TOT sandwiches causing the clay to swell or shrink.

18
Q

What happens to the surface area of an object if it is sliced up into smaller pieces?

A

Its surface area increases.

19
Q

What happens when water molecules enter the gaps between the TOT sanwiches?

A 
The cations (+) are attracted to the negatively charged oxygen ions on the surface creating a positively charged layer of ions. 
This occurs on both sides of the clay particle.
20
Q

How can the size of the clay mineral be determined?

A

By the amount of charge/cations on the surface.

21
Q

What do the mechanical properties of clay depend on?

A

The specific surface area.

22
Q

What is the classification of clay based on?

A

Plasticity.

23
Q

What creates a plastic material?

A

The fine flaky particles and the binding of water to the surface.

24
Q

What type of soil is sand?

A

A non-plastic soil.

25
Q

What happens when you mix sand with lots of water?

A

It will create a layer of sand at the bottom of the jar.

26
Q

What type of soil is clay?

A

A plastic soil.

27
Q

What can happen to high plasticity clay?

A

It can become a pourable liquid when mixed with enough water.

28
Q

What has a greater influence on the engineering properties: the shape or the size of the particle?

A

The size.

29
Q

What are consistency limits?

A

The water contents at which the consistency changes from one state to the next.

30
Q

What are consistencty limits also known as?

A

Atterberg limits.

31
Q

What are the four consistencies of soil?

A

Solid, semi-solid, plastic, and liquid.

32
Q

What is the liquid limit?

A

The change of consistency from plastic to liquid.

33
Q

What is the plastic limit?

A

The change of consistency from plastic to crumbly.

34
Q

What is the shrinkage limit?

A

The boundary between semi-solid and solid.

35
Q

How is the shrinkage limit measured?

A

By placing moist clay into an oven until it’s dry. Then measure the volume change.

CE431 Engineering geology and soil mechanics (2 decks)

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