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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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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