Compaction

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This page contains MCQs based on Compaction, its effect, tests on compaction, the result of compaction 

1. In the Compaction test, with the increase in compaction energy

A) Both dry density and Optimum Moisture Content increases
B) Maximum dry density increases but Optimum Moisture Content decreases
C) Maximum dry density decreases but Optimum Moisture Content increases
D) Both dry density and Optimum Moisture Content decreases

... Answer is B
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2. What is the number of blows required for compacting each layer for 2.25L mould in compaction test?

A) 36
B) 25
C) 56
D) 31

... Answer is C
For 1L mould 25 blows per each layer shall be provided
 

3. Which among the following has highest OMC?

A) Gravel
B) Silt
C) Sand
D) Clay

... Answer is A
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4. Factors affecting the compaction are

A) Water content
B) Compactive energy
C) Soil type
D) All the above

... Answer is D

 

5. Vibrator roller are useful for compacting__________

A) Cohesion less soil
B) Crushed rocks
C) Clayey soil
D) Gravel

... Answer is A

 

6. Clayey soil are best compacted by

A) Vibration
B) Impact
C) Kneading
D) All the above

... Answer is C

 

7. Compaction of soil is measured in terms of

A) dry density
B) Compressibility
C) Permeability
D) Specific gravity

... Answer is A

 

8. Optimum moisture content is the moisture content at which

A) Permeability is more
B) Settelment is maximum
C) Shear stength is less
D) dry density is maximum

... Answer is D

 

9. Clay particles on the wet side of optimum moisture content exibits

A) Honeycomb structure
B) Flocculent structure
C) Dispersed structure
D) Single grained structure

... Answer is C
For a given compactive effort, soils have a flocculated structure on the dry side (i.e. soil particles are oriented randomly), whereas they have a dispersed structure on the wet side (i.e. particles are more oriented in a parallel arrangement perpendicular to the direction of applied stress)
 

10. The 95% saturation line and 5% air voids line are______

A) Different
B) Same
C) May or may not be same
D) Can not be said

... Answer is A
100% saturation line and 0% sair void line are same
 

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What is Compaction?

What is Compaction?

Compaction is the compression of soil mass mechanically so that air present in the voids escape and thus improve its engineering properties. 

As a result of compaction, 

• Shear strength increases
• Compressinbility increases
• Permeability decreases

What are the tests on compaction?

There are mainly two tests conducted 

• IS Light Compaction or Standard Compaction test
• IS Heavy Compaction or Modified Proctors test

Features of tests	IS Light Compaction	IS Heavy Compaction
Weigth of hammer	2.60Kg	4.90Kg
Height of freefall	31cm	45cm
Number of layers	3	5
Number of blows per each layer	25	25
Volume	1L	1L

What is Optimum Moisture Content(OMC)?

It is the water content at which maximum dry density is obtained

What happens when compaction energy increases?

The comapction test is repeated for different water contents and in each case dry density is obtained and a graph is plotted between dry density and water content.

As Compaction increases dry density increases, but OMC decreases.It is evident from the graph. 

Comparison when compaction is done in finer soil and coarser soil? 

Finer soil has higher OMC and less maximum dry density. But why?

Finer soils have 

• more surface area and hence more OMC.
• Larger voids and hence lesser dry density

Compaction Equipments

Tampers	Manual compaction
Smooth wheel rollers	Granular or crushed rocks
Pneumatic tyred rollers	For all soils
Sheep foot roller	Clay
Vibratory rollers	Sand
smooth heavy roller	gravel in WBM road