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CIVE40009 - Geotechnics > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

What is the equation for relative compaction?

A

RC=⍴_d/⍴_dmax

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2
Q

What is compaction?

A

Process of increasing the dry density of soil by reducing the volume of air

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3
Q

When do you compact soil?

A

Partially saturated soil

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4
Q

When does consolidation occur in soil?

A

When it is saturated

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5
Q

How can volume be reduced by consolidation?

A

Removal of water

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6
Q

How can volume be reduced by compaction?

A

Removal of air

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7
Q

How can soil densification happen by compaction?

A

Through the application of external loads and mechanical mixing.

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8
Q

How can soil densification happen by consolidation?

A

Through the application of external loads.

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9
Q

Why do we compact soil?

A

To improve soil properties

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10
Q

What properties will be increased or reduced during compaction?

A
  • Increase stiffness (reduce settlement)
  • Increase strength
  • Reduce permeability
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11
Q

When would compaction be useful?

A

For road embankments nd retaining walls so no settlement occurs

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12
Q

What are some compaction methods?

A
  • Static load/pressure
  • Kneading
  • Impact
  • Vibration
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13
Q

How does static load/pressure work?

A

Put something heavy on material, use black rollers

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14
Q

How does kneading work?

A

Circular movements that cycle through the grains and move them around to find more stable position, steel rollers, and rubber wheels

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15
Q

How does impact work?

A

More violent dynamic using a load

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16
Q

What method can be used for fine-grained materials?

A
  • Kneading and impact
17
Q

What methods can be used for coarse-grained material?

A
  • Vibration and static load/pressure
18
Q

What is the lift thickness?

A

Thickness of the layer you can put on soil

19
Q

What are the 3 methods for quality control?

A
  1. Sand Cone Test
  2. Ballon Test
  3. Nuclear density test
20
Q

How can you check the soil quality?

A

Regularly measure the density of the material

21
Q

What are the steps for the sand cone test?

A
  1. Calibrate material
  2. Pick a good testing spot and representative
  3. Prep testing location
  4. Dig hole and keep moisture and collect soil
  5. Place and open the sand cone
  6. Close the valve and measure the final weight
  7. Calculate bulk and dry soil
22
Q

What are the steps for the ballon test?

A
  1. Choose a test spot
  2. Prep test location
  3. Adjust the ballon pump
  4. Dig a hole and collect soil
  5. Adjust the balloon pump and take the volume
  6. Calculate bulk and dry soil
23
Q

Before you go to the field what must you do?

A
  • Do lab tests
  • Look at British standard and ASTM
24
Q

How can compaction be analysed?

A

From a dry density and water content graph

25
Q

What is the saturation line?

A

The theoretical line says there is no more void space so can’t be compacted anymore

26
Q

What does it suggest when soil is at the beginning of the P_d and W graph?

A
  • Too little water then glue between them - voids mostly air
  • Meniscus water
27
Q

What happens when there is excess water in the soil?

A

Excess water displaces soil particles

28
Q

What does increased water do to the soil?

A
  • Makes the soil more workable
29
Q

How can compaction be tested using the Proctor Method?

A
  • Start from a low water content 2-3%
  • Minimum of 5 samples
  • Load samples in layers and compact with ahammer
  • Calculate P_d
  • Plot compaction curve
  • Establish w_opt and P_dmax
30
Q

How can the P_d be calculated from the Proctor Method?

A
  • Know the volume of the layer
  • Extract the material that’s inside and measure the mass
  • Can find bulk density and dry density
31
Q

How does soil type affect the curve on the density and water content diagram?

A

Maximum dry density decreases whereas the optimum water content increases with decreasing particle sizes and increasing plasticity

32
Q

How does compaction effort affect the curve?

A

For a given soil, the maximum dry density increases whereas the optimum water content decreases with increasing compaction effort

CIVE40009 - Geotechnics (13 decks)

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