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MSc Eng. Geology > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Flow Lines

A

Lines of Fluid Flow

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2
Q

Equipotential Lines

A

Connects points of equal total head (include both ground lines)

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3
Q

Rules for Flow Net

A
  1. Lines must cross at 90 degrees

2. Must have equal lines (circle inside)

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4
Q

Flow Net is what equation graphically

A

La Place

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5
Q

Total Head

A

(Elevation Head) + (Pressure Head)

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6
Q

Change in Head (delta h)

A

(Elevation of top water) - (Elevation of Bottom water)

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7
Q

Hydraulic Gradient

A

i=(Change in head) / (# of drops)

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8
Q

Total Head at certain point equation

A

Htotal,c=(total head) - (i)*(# of drops)

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9
Q

Elevation Head

A

Helevation= elevation at point

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10
Q

Pressure Head

A

Amount of pressure at point, use Total Head formula to plug and chug pressure and total

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11
Q

Total Flow Equation

A

q=kh(Nf/Nd)

  • k:given
  • h:Change in head
  • Nf: # elements to bottom of pile
  • Nd: # of drops
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12
Q

What does a Sheet Pile do

A

-sheet pile lengthens the flow path, this creates more equipotential drops, more drops lessens the total head which lessens the pressure head and therefor lessens pressure under the damn

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13
Q

Where is hydraulic gradient the greatest

A

i=(change in head) / (length)
Change in head stays the same, and the smaller the length means larger gradient so the smallest element has the greatest (usually under the pile)

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14
Q

4 ways to deal with groundwater

A
  1. Open pumping
  2. Pre-draining
  3. Cutoffs
  4. Exclusion
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15
Q

Open Pumping

A
  • least expensive solution to dewatering

- pump water as it fills the hole

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16
Q

Pre-Draining

A

-look up better definition from book

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17
Q

Cutoffs

A

-look up from book

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18
Q

Exclusions

A

-look up from book

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19
Q

Ways to construct a Cutoff wall

A
  • diaphragm walls
  • slurry trench
  • secant drilled shaft wall
  • tremie seals
  • permeation grouting
  • ground freezing
  • *get definitions from book
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20
Q

Total Stress, sigma

A

-weight of everything on top of that point

=(density of material) * (height of that material) + …..

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21
Q

Porewater Stress, u

A

u=(density of water) * (height of water table)

22
Q

Effective Stress, sigma bar

A

=(total stress) - (porewater stress)

=sigma - u (in psf)

23
Q

Relations for void ratio and specific gravity

A

e=(w*Gs)/(Sr)

(Unit weight)d=(Gs*Unit weight water)/(1+e)

Unit weight=(Unit weight)d * (1+w)

(Unit Weight)d= (unit weight)/(1+w)

24
Q

Relative Compaction, Cr

A

Cr=[(unit weight)d]/[(Unit weight)d max] x 100%

25
Q

What is a Heave

A

-When excavation is lifted

26
Q

When does a heave occur

A

When effective stress=0 which means totals stress=porewater stress

27
Q

Capillary Rise

A

Ability of water to move upwards against gravity due to adhesion of the fluid and the solid wall

28
Q

Quick Condition

A

upward water pressure gradient and water flow reduce the effective stress (quick sand)

29
Q

Forms of Compaction

A

-Runways, Earth Damns, Roadways, Embankments, Levees

30
Q

4 Types of Compaction rigs

A
  1. Sheepsfoot Roller
  2. Rubber Tired Roller
  3. Steel Wheeled Roller
  4. Vibratory Roller
31
Q

Why compact?

A
  • increases engineering properties of the soil
  • stress applied to lower amount of air and void space in soil
  • Densifies the soil
32
Q

What does compaction do to Engineering Properties?

A
  • Higher strength
  • Lower compressibility
  • Lower permeability
  • Less tendency to absorb water
33
Q

What does compaction do to Performance of the fill?

A
  • Greater stability
  • Less settlement
  • Less seepage
  • Reduced Shrink/Swell
34
Q

Laboratory Compaciton techniques vs. field use

A
  • Impact compaction=None
  • Static compaction =Steel/rubber wheeled roller
  • Kneading Compaction=Sheepsfoot roller
  • Vibratory=Vibratory Roller
35
Q

Calculate Pore Pressure at a Point

A

Pore Pressure=[(Nd/Delta h) + Height of water above] * (Unit weight of water)

36
Q

Compute moisture content for 80% and 100%

A

W=S( (unit weight of water) / (dry unit weight) - (1/Gs)) x 100%

37
Q

Compute Relative companion, Cr

A

(Dry unit weight)=(unit weight) / (1+w)
Cr=(dry unit weight) / (dry unit weigh max)

Standard is Cr>90%

38
Q

Sand Cone Steps

A
  • weight of soil
  • Volume of soil
  • Density of soil
  • water percent of soil
  • dry unit weight of soil
  • Relative compaction of soil
39
Q

Pressure in Water Formula

A

Height of head * Unit weight of water

40
Q

How does compaction differ for a landfill and that of a fill to support a building

A

Fill= based on percent of dry unit weight, Has high dry unit weight which means low compressibility and high strength (range near 10%)
Landfill=concerned in k value, may specify compacted WET of optimum

41
Q

What is a sand cone and how is it used

A
  • device to measure volume in the field

- Used to get dry unit weight

42
Q

What type of soil is best compacted with a sheepfoot compactor

A

Clay and will also do silt

43
Q

What type of soil is best compacted with a vibratory compactor

A

Granular (Sand)

44
Q

How is a Piezometer reading calculated

A

-find the total head at that area

h(total)=Height of water - (change per drop * # of drops)

45
Q

What happens when an excavation has a negative effective stress?

A

Clay will “blow out” or heave

46
Q

Four types of Field Compaction Tests

A
  • Sand cone
  • Rubber Balloon
  • Drive Cylinder
  • Nuclear Density
47
Q

Four ways to compact soil in the laboratory

A
  • Impact (Dropping weight on it)
  • Static (Load is applied and held)
  • Kneading (small foot is loaded and unloaded multiple times)
  • Vibratory (for sand and gravel, vibrated)
48
Q

Why in a lab is impact compaction most popular?

A

-been around the longest so a large data base

49
Q

Standard proctor test vs. Modified

A

Modified has a larger 10 lb weight dropped from a higher 18” distance with 5 layers instead of 3

50
Q

Why does dry density lower after optimum water content?

A

At optimum water content the soil is considered saturated, so adding more water would just replace soil and decrease the dry density

MSc Eng. Geology (50 decks)

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