Expansive Soils Flashcards

1
Q

Active Earth Pressure Formula:

A

σ’h = ka * σ’v - 2 * c’ * SQRT(ka)

where,
ka = (1-sin(Φ))/(1+sin(Φ))

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2
Q

Passive Earth Pressure Formula:

A

σ’h = kp * σ’v + 2 * c’ * SQRT(kp)

where,
kp = 1/ka

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3
Q

What is expansive soils

A
  • Swelling of wetted soil
  • Shrinkage of dry soil
  • Unsaturated to saturated and saturated to unsaturated
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4
Q

Clay Minerals in descending order

A
  • Montmorillonite
  • Vermiculite
  • Illite
  • Kaolin
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5
Q

Where does most movement occur

Expansive Soil

A

1-4m

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6
Q

Most susceptible structures are

Expansive Soil

A
  • Pavements
  • Canals
  • Pipelines
  • Retaining walls
  • House Footings
  • Light industrial Buildings
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7
Q

What is Soil suction

Expansive Soil “…”

A

The soil’s affinity for water

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8
Q

The 3 types of suction

Expansive Soil

A
  • Matric Suction
  • Solute Suction
  • Total Suction

Total = Matric + Solute

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9
Q

Affect of a smaller diameter for matric suction

Expansive Soil

A
  • The greater the curvature
  • The higher the liquid tension
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10
Q

What is the formula for effective stress in saturated soil

Expansive Soil

A

σ’ = σ - Ua + χ(Ua - Uw)

Ua = pore air pressure
Uw = pore water pressure
(Ua-Uw) = Matric suction

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11
Q

What is the parameter “χ”

Expansive Soil - Used for Soil suction

A
  • It varies between 0 and 1
  • =1, Saturated
  • Empirical estimates of variation of χ based on ratio of Um to Uae
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12
Q

What is pF given as,

Expansive Soil suction in pF = ….

A

pF = log(suction in kPa) +1.01

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13
Q

When is it active earth pressure

Retaining wall

A

When the wall is leaning away from the soil

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14
Q

When is it passive earth pressure

Retaining wall

A

When the wall is leaning into the soil.

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