9) Compaction and earthworks

Question 1

What is compaction?

Answer 1

Densification of a soil by mechanical plant so that soil particles pack more closely together associated with a reduction of air voids.

Question 2

What is consolidation?

Answer 2

Reduction of void volume by removal of water, normally due to the application of sustained loading.

Question 3

Compaction leads to what three things?

Answer 3

Increased strength
Reduced compressibility
Reduced permeability

Question 4

What influences compaction?

Answer 4

• Moisture content
• Compactive energy
• Soil type

Question 5

What is the soil like at low m/c?

Answer 5

Soil is stiff and hard to compress
Low dry density
Low degree of saturation

Question 6

Medium m/c?

Answer 6

Water acts as lubricant and softens the soil
higher dry density
higher degree of saturation

Question 7

High m/c?

Answer 7

Soil is even softer and weaker
air is in discrete bubbles and cannot be expelled easily
increasing water leaves less room for soil so the dry density is reduced

Question 8

How is soil compacted in the field?

Answer 8

Pressure
Vibration
Impact

Question 9

What do we use to compact soils?

Answer 9

Grid rollers
Vibrating rollers
Pneumatic tyred rollers
Tamping plates

Question 10

What are the 4 in situ density tests? (for check m/c in the field)

Answer 10

Core cutter method (for clay soils)
Sand replacement tests
Balloon density tests
Nuclear methods