ye yes its mandatory

1. INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
Compaction
Presented By
Dr. Akanksha Tyagi
Assistant Professor
Civil Engineering Department
IIT Roorkee

2. What is Compaction?
• Soil used a construction material.
• Example: Highway
embankments, Earth dams.
• A type of soil improvement
technique to improve soil density
and strength characteristics.
• For construction of
embankment: Soil is placed and
then compacted by mechanical
means so that in unit volume,
large volume of solids are
achieved.
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3. Compaction
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Advantages of Compaction:
i. Heavily compacted soils contain few large
pores, less total pore volume and,
consequently, a greater density.
ii. Has a reduced rate of both water infiltration
and drainage.
iii. Increased soil strength and stiffness of in-
situ soils
iv. Increased shear strength by friction from
interlocking of particles
v. Reduced Settlement and risk of shrinking or
expanding
Why Compaction is required?
Compaction decreases the likelihood of settlement after a building, roadway,
runway or parking lot is constructed. Settlement could result in premature
pavement failure, costly maintenance or repairs.
Soil compaction is the process of applying pressure to densify a soil by
reducing the void space between soil particles.
Before Treatment After Treatment
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Difference between Compaction and Consolidation
Compaction
i. Instantaneous
ii. Soil is unsaturated
iii. Densification due to reduction in air-
voids at given water content.
iv. Specified compaction techniques
used
Consolidation
i. Time-dependent
ii. Soil is completely saturated
iii. Volume reduction due to expulsion
of pore water
iv. Occurs due to application of load
placed on soil

5. Standard Proctor Test
• Invented in the 1930s by R. R. Proctor, in Los Angeles,
California.
• Standard amount of energy is imparted to a constant
volume of soil mass at various moisture contents and
that moisture is obtained for which unit volume of soil
mass possesses maximum weight of solids.
• Test focuses on the change of a sample’s moisture
content to derive the optimum water content (wopt).
• As per IS 2720 (Part 7): Called as Light Compaction
Test, volume of mould is 1000cc, weight of hammer is
2.6kg, drop height is 310mm.
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30
cm

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• The compaction water content (w) of the soil sample is calculated using the average of the three
measurements obtained (top, middle and bottom part of the soil mass).
• The dry unit weight (γd) is calculated as follows:
• 𝛾𝑑 =
𝑊−𝑊𝑚
(1+𝑤) 𝑉
• where: W = the weight of the mold and the soil mass (kg)
• Wm = the weight of the mold (kg)
• w = the water content of the soil (%)
• V = the volume of the mold (m3, typically 0.033m3)
• This procedure should be repeated for 4 more times, given that the selected water contents will
be both lower and higher from the optimum.

8. Zero Air-Void Line
1/28/2024 Anumita Mishra, IIT Roorkee 8

9. Modified Proctor Test
• Introduced after World War II, in the 1950’s, to
simulate compaction required for airfields to support
heavier aircrafts.
• The cylindrical mould is the same.
• The drop weight is increased to 4.5kg and the
dropping height to 45 centimeters. In addition, the
soil is compacted in 5 layers with 25 blows per layer.
(ASTM standard)
• Test conducted for 5 moisture contents to obtain the
optimum water content (wopt), for which the value of
the dry unit weight is maximum (γd,max).
• As per IS 2720 (Part 8): Called as Heavy Compaction
Test, volume of mould is 1000cc, weight of hammer is
4.9kg, drop height is 450mm.
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Typically,
𝛾𝑑 𝑚𝑎𝑥 = 16 to 20 𝑘𝑁/𝑚3
OMC = 10-20 %

11. Factors affecting Compaction
1. Water Content
2. Compactive Effort
3. Type of Soil
4. Method of Compaction
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12. Water Content
1. Lubrication Theory (by Proctor):
Simple theory, not widely accepted.
• The soil is stiffer and more resistant to compaction at low water content.
• With increase in moisture content, particles develop larger and larger film of water around its
surface. It is easier to work and move the particles closer with the same compactive effort.
• If the water content rises, the dry density of the soil rises as well, until the optimum water content is
reached. At that point, the air voids have reached a volume that is nearly constant.
• The air voids do not decrease when the water content rises, but the total voids (air plus water) do,
and the dry density decreases.
• At higher moisture content, water starts to replace the soil particles and since 𝛾𝑤 ≪ 𝛾𝑠, dry unit
weight decreases.
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“Moisture Content and dry unit weight relationship ”: Two theories exists to explain why
moisture content affects the dry unit weight.

13. 2. Double Layer Theory (Lambe 1958):
• Attractive forces due to Van der Waals forces act between two clay particles. Due to
this, soil particles tend to floc together. Repulsive forces due to double layers of
adsorbed water.
• If double layer is not fully developed, the forces are very high, and there is net
attractive force between the soil particles.
• When compactive effort is applied, it is difficult to move particles with respect to
each other because of strong attractive forces (just like flocs of tiny magnets).
• With same compactive effort, dry density is less.
• As moisture content increases, double layer expands and inter-particle repulsive
forces increase. The particles easily slide over one another and get packed more
closely, causing higher dry unit weight.
• At OMC, double layer is fully developed.
• With further increase in moisture content, no further increase in double layer. Water
occupies the space which otherwise would have been occupied by soil grains. Thus,
dry density decreases.
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Regardless of the method of compaction, soils
compacted at a water content less than the optimal
water content have a flocculated structure.
Soils compacted at a water content higher than the
optimum water content have a dispersed structure if
large shear strains are induced, and a flocculated
structure if the shear strains are minimal

15. Compaction Effort
• This effect of increase in compaction is significant only until the water content reaches its
optimum level.
• After that level, the volume of air voids becomes almost constant and the effect of
increased compaction is not significant.
• It should be noted that the maximum dry density does not go on increasing with an
increase in the compactive effort.
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• Compactive effort is a measure of the mechanical
energy applied to a soil mass.
• It has units of energy per unit volume, or N-m/m3.
• In field, compactive effort is the number of passes
of the roller of a certain type and weight on a given
volume of soil.
• The optimum water content required for
compaction decreases with an increase in the
compaction effort.

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• Due to higher compactive effort, increase
in dry density on dry side > Increase in dry
density on wet side due to same increase in
effort.
• At Dry of optimum, fine-grained soils are
always flocculated, whereas at Wet of
Optimum, the fabric becomes more
oriented or dispersed.
• If the compactive effort is increased, the
soil tends to become more oriented, even
dry of optimum.
• Wet of optimum, the fabric at point D will
be somewhat more oriented than at point
B.
• For same w, From A to E, much more
orientation (dispersion) takes place as
compared to change in orientation
between C and D.
Slightly
Dispersed
Flocculated
Dispersed
Compaction Effort

17. Calculation of Compaction Effort
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18. Type of Soil
• Coarse grained soils can be compacted to
higher dry density than the fine grained
soils.
• The maximum dry density decreases if the
quantity of fines is increased to an amount
more than that required to fill voids in the
coarse grained soils.
• A well graded soil obtains a much higher
dry density than a poorly graded soil.
• Cohesive soils have large surface area, thus
have greater OMC and lower maximum dry
unit weight. High plasticity gives higher
OMC, but lower MDD.
• Poorly graded soils achieve minimum unit
weight.
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19. Effect of Compaction on Soil Properties
• Structure: Dry side of OMC: Flocculated structure
Wet side of OMC: Dispersed structure
• Permeability: If dry unit weight increases, permeability decreases (voids decreasing)
Compaction with dry of OMC: Permeability decreases sharply with increase in water
content. This is due to improved orientation of particles and causes decrease in voids
Minimum permeability achieved for compaction slightly above OMC.
• Compressibility: At low stress level: Soil compacted at wet side are more compressible.
For dry side of OMC, flocculated structure does not allow particles to be readily displaced.
At high stress level, opposite trend observed. Since bonds are already broken, flocculated
structure has large voids and undergoes compression.
• Shrinkage and Swelling: At Dry of OMC, random particles arrangement and water
deficiency: thus swells more. At Wet of OMC, exhibit more shrinkage on drying. Parallel
orientation allows particles to pack efficiently.
• Pore pressure: Soil compacted Wet of OMC have higher pore water pressure.
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Thank You