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

Difference between Quick sand and Quick soil

 

Quick Sand	Quick Soil
Quick sand is a hydraulic condition, not a type of soil	Quick soil is a type of soil
Definition At critical condition, effective stress being zero, shear strength of cohesionless soil becomes zero hence, soil behaves like a boiling liquid.	Definition A soil deposit that is reasonably stable if undisturbed, but suddenly becomes loose when disturbed. Or When sensitivity of soil > 16
Observed in fine sand and silt	marine clay
Also known as Quick condition, Boiling condition	Also known as Highly sensitive, quick clay

What is the difference between unit dry density and unit weight of soilds Γ_dry  vs Γ_solid?
Γ_{dry    =   Weight of soil solids / Total volume}  
Γ_{solid  =  Weight of soil solids / Volume of soil solids}

But dry weight of soil and weight of soil solid are the same. 

Γ_{solid is always greater than} Γ_dry.Why?

_{In case of}  Γ_{solid calculation only volume of soil solid is taken, which yields constant values where as} 

_In Γ_{dry Total volume is taken including Volume of voids, Volume of water present in pores,Volume of Soil solids. So the denominator value increases and so does the value of} Γ_dry.

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Difference between Isotropy and Anisotropy

 

Anisotropy	Isotropy
Property of material depends on direction	Property of material is independent of direction
Particle substance do not have same mechanical and thermal properties in every direction	Particle substance have uniform mechanical and thermal properties in every direction
Different properties in different direction	Same properties in different direction
More than one refractive index	Only one refractive index
Examples Wood, composite material, All crystals except cubical crystals	Examples Crystals with cubic symmetry , metals, glass

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Difference between Crystalline and Amorphous structure

Crystalline	Amorphous
Well defined edges and faces	Irregular surface
Has definite pattern, regularly arranged	No definite pattern, irregular arrangement
These have a long range order meaning- there is a regular pattern of arrangement of particles which repeats itself periodically over the entire crystal.	These have short range order meaning- regular predictable arrangement of the atoms are seen over a short distance
Sharp melting point	Has varying range of melting point
When cut with a sharp-edged tool, they split into two pieces with plain and smooth surfaces.	When cut with a sharp-edged tool, they cut into two pieces with irregular shapes.
Anisotropic in nature	Isotropic in nature
Also known as true soilds	Also known as pseudo-solids or supercooled solids
Examples Diamond, Ice, Sugar, Metals	Examples Rubber, Plastic, Gel, Glass

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Difference between Helical and Leaf springs

Helical Spring	Leaf Spring
	Source Wikipedia
It is made by winding a constant diameter wire in the form of helix.	It is made by clamping series of flat plates of varying length one above another.
Spreads the load to a single point	Spreads the load more widely over the vehicle's chassis
Resulting shape of helical spring is cylindrical	Resulting shape of leaf spring is semi-elliptic.
It offers small amount of flexibility in transverse direction.	It does not offer flexibility in transverse direction.
Load bearing capacity of this type of spring is comparatively lower.	Load bearing capacity of this type of spring is much higher.
It is light weight and cheaper.	It is heavy and costly.
It tends to absorb shocks and vibrations and thus provide a comfortable ride.	Leaf spring tends to lift of the vehicle body when it experiences bumps hence uncomfortable ride.
Common application areas Spring balance, shock absorbers in motor bikes, pens etc	Common application areas Vans and Trucks, SUVs etc

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