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Intro to Geotechnical Engineering > EXAM 1 > Flashcards

EXAM 1 Flashcards

1
Q

Void Ratio

A

e = Vv / Vs

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2
Q

Porosity

A

n = Vv / V

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3
Q

Void Ratio and Porosity Relations

A 
e = n / (1-n)
n = e / (1+e)
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4
Q

Degree of Saturation

A

S = Vw / Vv

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5
Q

Water Content

A

w = Ww / Ws = Mw / Ms

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6
Q

Total Unit Weight

A

γ = W / V

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7
Q

Dry Unit Weight

A

γd = Ws / V

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8
Q

Relationship between γ and γd

A

γ = γd * (1+w) = Ws * (1+w) / V

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9
Q

Unit Weight of Water

A

γw = 9.81 kN/m^3

= 62.4 lb/ft^3

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10
Q

Solid Unit Weight

A

γs = Ws / Vs

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11
Q

Specific Gravity

A

Gs = γs / γw

G water = 1 @ 4 C

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12
Q

Total Density

A

ρ = M / V

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13
Q

Dry Density

A

ρd = Ms / V

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14
Q

Solid Density

A

ρs = Ms / Vs

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15
Q

Density and Unit Weight Relation

A 
γ = ρ * g
g = 32.2 ft/sec 9.81 m/sec
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16
Q

Coarse

A

Rel bigger
Large voids
Low SSA
Equidimesnsional

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17
Q

Fine Soil

A

Very small voids
Large SSA
Platy shape ( sheets of paper )
Important surface forces

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18
Q

Main Mineral Group

A

Silicates

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19
Q

Basic Structural Unit of Silicates

A

Silica Tetrahedron

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20
Q

Composition of Coarse Materials

A

Gravel and sand fractions of soil are composed of non-clay materials

Quartz

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21
Q

The building blocks for clay materials

A

Silica Sheets

Octahedral Sheets (Tri and Di Octahedral)

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22
Q

Dioctahedral

A

Octahedral sheet with +3 element such as Al instead of +2 element
More holes than trioctahedral

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23
Q

Trioctahedral

A

Formed by octahedral units consisting of 6 hydroxyl (OH) surrounding an magnesium atom

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24
Q

Kaolinite

A 
1:1 or 2 sheets per layer 
One silica sheet and one tetrahedral sheet
Large platy shaped particle 
Strong glue between layers
Low SSA (5-15 m2/g)
25
Q

Isomorphous Substitution

A

Occurs in the formation of silicate materials
Substitution of one atom for another
Instead of Si atom +4 there is Al atom +3
Net unit charge deficiency increases
Distortion of the lattice

26
Q

Illite

A 
2:1 or 3 sheets per layer 
More charged than kaleonite
Octahedral sheet bonded to 2 silica sheets 
Glue is not very strong 
Platty shaped particles 
Low SSA (80-100 m2/g)
27
Q

Montmorillonite

A

2:1 or 3 sheets per layer
Dicotahdedral sheet bonded to 2 silica sheets
Cations can quickly come in and out (loose)
Due to small amount of iso sub makes exchangeable
Large amount of water in the space of the layers
Modest amount of glue ( Na, Ca, Mg)
Very high SSA

28
Q

Specific Surface Area

A

SSA= Surface Area / mass

29
Q

The two faces of all platy particles have a

The edges of particles have

A

Negative charge caused by iso sub that is not neutralized by interlayer cation bonding

Positive charge

30
Q

Diffuse Double Layer (DL)

A

When water is present cations and anions can float around the clay particles forming a diffuse double layer
The water is held to the clay particles by forces of attraction
Richer in cation the close to the particle

31
Q

Absorbed water layer

A

The first 10-15 Angstroms of water adjacent to the mineral surface
Essentially acts as part of the structure of the clay particle
So close that it doesn’t freeze

32
Q

Double layer repulsion

A

Water molecules want to enter the double layer to reduce cation concentration by separating particles by reducing alkalinity which creates an edge to face electrical attraction

33
Q

Flocculate

A

Two particles tend toward each other and become attached edge to face

34
Q

Disperse

A

Two particles tend to move away due to no attraction

35
Q

Unified Soil Classification System (USCS)

A

Standard soil identification test baed on particle size analysis and Atterberg limits
Soil types - Gravel, sand, silt, clay organic, peat

36
Q

Gravel

A

less than 50% passing sieve #4 (4.75 mm)

37
Q

Sand

A

more than 50% passing sieve #4 (4.75 mm)

less than 50% passing sieve #200 (0.075 mm)

38
Q

Silt (M)

A

More than 50% passing sieve #200 (0.075 mm)

Below A-line

39
Q

Clay (C)

A

More than 50% passing sieve #200 (0.075 mm)

On or above A-line

40
Q

Organic (O)

A

More than 50% passing sieve #200 (0.075 mm)

(Liquid Limit dried / Liquid Limit not dried) less than 0.75

41
Q

Peat (Pt)

A

More than 50% passing sieve #200 (0.075 mm)

Mostly organic matter

42
Q

Particle Size Distribution Plot

A 
Logrimithic Scale
x axis - Particle Size (mm)
y axis - Percent Finer by Weight 
s curve 
use to find percent finer than 0.075 mm
43
Q

Soil Uniformity Coefficient

A

Cu = D60 / D10 = Diameter at 60% / Diameter at 10%
The higher Cu , the less uniform the soil, more horizontal curve
Cu = 1 means very uniform, straight curve

44
Q

Coefficient of Curvature or Gradation

A

Cc = (D30)^2 / (D10 * D60)

Smaller and higher numbers show gaps in the curve (two types of soil)

45
Q

Plasticity Atterberg Limits

A

Liquid Limit, Plastic Limit, Shrinkage Limit

46
Q

Liquid Limit

A

Fluid soil-water mixture

The water content (%) after 25 blows of Casagrande cup

47
Q

Plastic Limit

A

Enough water where the soil doesn’t crack after working with it
Water content at which 1/8” diameter thread crumbles

48
Q

Plasticity Index

A

The difference between the liquid limit and plastic limit
PI = LL - PL
Equals the water content within which soil is in the plastic state

49
Q

Compaction

A

Densification of soil by the application of mechanical energy

50
Q

Methods of compaction

A

Fine : Impact and kneading using rollers controlled by relative compaction

Coarse : Static or dynamic/ vibration using vibratory and tamping controlled by relative density

51
Q

Proctor Test

A

A compaction test to determine the optimum moisture content and density for a soil

52
Q

Compactive Effort

A

Measure of the mechanical energy applied to the soil mass

The more applied, the more dense the material and dry unit weight increases

53
Q

4 key variables in compaction of fine grained soils

A
  • Dry density or dry unit weight
  • Water content
  • Compactive effort
  • Soil type
54
Q

Optimum water content is located on proctor test plot

A

Where the dry unit weight (densification) is maximized

55
Q

Parabolic shape on on proctor test plot

A

Water acts as lubricant until a point

56
Q

The compaction curve never reaches 100% saturation

A

Due to voids

57
Q

On proctor test plot, as compactive effort increases

A

The dry unit weight increases and the optimum water content decreases (left)

58
Q

On proctor test plot, as plasticity increases

A

Dry unit weight decreases

Intro to Geotechnical Engineering (3 decks)

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