Lecture 6 compaction & consolidation

fundamentals of soil mechanics

1. Compressibility
Consolidation
Compaction
Prepared by: Elias A.
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2. COMPACTION
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3. What is compaction?
A simple ground improvement technique, where the soil is densified
through external compactive effort.
Compaction is the application of energy to soil to reduce the void
ratio
This is usually required for fill materials, and is sometimes used
for natural soils
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4. Purposes of Compaction
Compaction reduces settlements under working loads
 decreases the amount of undesirable settlement of structures
Compaction increases the strength characteristics of soils
increase the bearing capacity of foundations constructed over them
 increases the stability of slopes of embankments
Compaction makes water flow through soil more difficult
Compaction can prevent liquefaction during earthquakes
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5. at w = 0,
at w = w1
The moisture content at which the maximum dry unit weight is attained
is generally referred to as the optimum moisture content.
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7. (a) mold; (b) hammer
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14. Factors affecting Compaction
The main factors affecting compaction are:

Moisture content

•Soil type

•Compactive effort
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15. Soil type
-grain-size distribution,
-shape of the soil
grains,
-specific gravity of soil
solids, and
-amount and type of
clay minerals present
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16. Compactive effort
There is no unique curve.
Increasing compactive
effort results in:
•Higher maximum dry
density
• Lower optimum water
content
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17. Field Compaction
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19. Compressibility of soils
One-dimensional consolidation settlement of fine-grained soils
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20. A stress increase caused by the construction of foundations or
other loads compresses soil layers.
The compression is caused by
(a)deformation of soil particles,
(b)relocations of soil particles, and
(c)expulsion of water or air from the void spaces.

In general, the soil settlement caused by loads may be divided
into three broad categories:
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21. These are
I.Elastic settlement (or immediate settlement), which is caused by
the elastic deformation of dry soil and of moist and saturated soils
without any change in the moisture content.
II.Primary consolidation settlement, which is the result of a volume
change in saturated cohesive soils because of expulsion of the
water that occupies the void spaces.
III.Secondary consolidation settlement, which is observed in saturated
cohesive soils and organic soil and is the result of the plastic
adjustment of soil fabrics.
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22. The total settlement of a foundation can then be given as
Note: When foundations are constructed on very compressible clays, the
consolidation settlement can be several times greater than the elastic settlement.
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23. Contact Pressure and Settlement Profile
Elastic settlement profile and contact pressure in clay:
( Flexible foundation
Rigid foundation
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24. The sand at the edge of a flexible foundation is pushed outward, and the deflection
curve of the foundation takes a concave downward shape.
Elastic settlement profile and contact pressure in sand
flexible foundation
rigid foundation
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26. The Process of Consolidation - The spring analogy
A: inside area of
the cross section
of the cylinder
Ps : load carried by
the spring
Pw: load carried
by the water
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29. 1D- Laboratory Consolidation Test
(oedometer test)
Purpose of the test
-to obtain soil data which is used in predicting the rate
and amount of settlement of structures founded on clay

- an apparatus known as an oedometer
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35. The maximum effective past pressure is called the pre-consolidation
pressure. 35

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39. Calculation of primary consolidation settlement
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49. C
c = 0.009( LL - 10)
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50. THANK YOU
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