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Definition:
Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air.
Solids
Water
Air
Solids
Water
Air
Compressedsoil
Load
SoilMatrix
γsoil (1) = WT1
VT1γsoil (2) =
WT1
VT2
γsoil (2) > γsoil (1)
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Why Soil Compaction:1- Increase Soil Strength 2- Reduce Soil Settlement3- Reduce Soil Permeability4- Reduce Frost Damage5- Reduce Erosion Damage
Soil Compaction in the Field:
1- Rammers
2- Vibratory Plates
3- Smooth Rollers
4- Rubber-Tire
5- Sheep foot Roller
6- Dynamic Compaction
Soil Compaction in the Lab:
1- Standard Proctor Test2- Modified Proctor Test
Standard Proctor Test Modified Proctor Test
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The Proctor Test (after Ralph R. Proctor, 1933)
95
96
97
98
99
100
101
102
103
104
105
15 17 19 21 23 25 27 29
w %
Dry
Den
sity
, pcf
Maximum drydensity = 102.5 pcf
optimum w % = 21.0
zero air voids curve
Example:The laboratory test for a standard proctor is shown below. Determine the optimum water content and maximum dry density. If the Gs of the soil is 2.70, draw the ZAV curve.
Solution:
γdry =γwet
Wc
100
%1+
Volume of Proctor Mold
(ft3)
1/301/301/301/301/301/30
Weight of wet soil in the mold (lb)
3.884.094.234.284.244.19
Water Content (%)
121416182022
Volume of Mold (ft3)
1/301/301/301/301/301/30
Weight of wet soil in the mold (lb)
3.884.094.234.284.244.19
Water Content
(%)
121416182022
Wet Unit Weight(lb/ft3)
116.4122.7126.9128.4127.2125.7
Dry Unit Weight(lb/ft3)
103.9107.6109.4108.8106.0103.0
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
10 11 12 13 14 15 16 17 18 19 20 21 22 23
γZAV =Gs γw
WcGs1+Sr
Water Content
Dry Density
Effect of Energy on Soil Compaction
HigherEnergy
Increasing compaction energy Lower OWC and higher dry density
In the fieldincreasing compaction energy
= increasing number of passes or reducing lift depth
In the labincreasing compaction energy = increasing number of blows
Soil Compaction in the Lab:
1- Standard Proctor TestASTM D-698 or AASHTO T-99
2- Modified Proctor TestASTM D-1557 or AASHTO T-180
Energy = 12,375 foot-pounds per cubic foot
Energy = 56,520 foot-pounds per cubic foot
Number of blows per layer x Number of layers x Weight of hammer x Height of drop hammer
Volume of moldEnergy =
MoistureContent
Dry Density
γd max
CompactionCurve for StandardProctor
(OMC)
γγγγd max
(OMC)
Zero Air Void CurveSr < 100%
Zero Air Void CurveSr =100%
Zero Air Void CurveSr = 60%
CompactionCurve for ModifiedProctor
For standard Proctor test
)ft/lbft375,12(m/kJ7.592
m10944.0
)layer/blows25)(layers3)(m3048.0)(s/m81.9(kg495.2E
33
33
2
⋅
−
=
×=
Effect of Soil Type on Soil Compaction
Nuclear Density Sand Cone
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