1. SOIL MECHANICS & TESTING
SOIL COMPACTION By
Kamal Tawfiq, Ph.D., P.E.
Fall 2008

5. Soil Compaction in the Field:
1- Rammers
2- Vibratory Plates 
3- Smooth Rollers
4- Rubber-Tire
5- Sheep foot Roller
6- Dynamic Compaction

6. gsoil (2) > gsoil (1) gsoil (1) = gsoil (2) = Definition:
Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air.
gsoil (2) > gsoil (1)
Load
Air
Air
Water
Water
Soil
Matrix
Compressed
soil
Solids
Solids
WT1
gsoil (1) =
WT1
gsoil (2) =
VT1
VT2

7. Water is added to lubricate the contact
Why Soil Compaction:
1- Increase Soil Strength
2- Reduce Soil Settlement
3- Reduce Soil Permeability
4- Reduce Frost Damage
5- Reduce Erosion Damage
Factor Affecting Soil Compaction:
1- Soil Type
2- Water Content (wc)
3- Compaction Effort Required (Energy)
Water is added to lubricate the contact
surfaces of soil particles and improve the compressibility of the soil matrix
Types of Compaction : (Static or Dynamic)
1- Vibration
2- Impact
3- Kneading
4- Pressure

8. Soil Compaction in the Lab: 1- Standard Proctor Test
Modified Proctor Test
Soil Compaction in the Lab:
1- Standard Proctor Test
2- Modified Proctor Test
3- Gyratory Compaction
Standard Proctor Test
Gyratory Compaction

9. Soil Compaction in the Lab: 1- Standard Proctor Test
gZAV =
Gs gw Wc Gs 1+ Sr
Soil Compaction in the Lab:
1- Standard Proctor Test
Dry Density
Zero Air Void Curve
Sr =100%
5.5 pound hammer
gd max 3
H = 12 in 4 2 5 1
25 blows
per layer
wc5
Compaction
Curve
wc1
wc2
wc3
wc4
Dry to
Optimum
Wet to
Optimum
gd1
gd2
gd3
gd4
gd5
(OWC)
Water
Content
Optimum
Water
Content
Increasing Water Content
gdry =
gwet Wc
100 % 1+
4 inch diameter compaction mold.
(V = 1/30 of a cubic foot)

10. Soil Compaction in the Lab:
1- Standard Proctor Test
ASTM D-698 or AASHTO T-99
2- Modified Proctor Test
ASTM D or AASHTO T-180
Zero Air Void Curve
Sr = 60%
Dry Density
Zero Air Void Curve
Sr =100%
gd max
Energy = 12,375 foot-pounds per cubic foot
Zero Air Void Curve
Sr < 100%
gd max
Compaction
Curve for Modified
Proctor
Energy = 56,520 foot-pounds per cubic foot
Compaction
Curve for Standard
Proctor
(OMC)
Moisture
Content
(OMC)
Number of blows per layer x Number of layers x Weight of hammer x Height of drop hammer
Volume of mold
Energy =

11. increasing compaction energy = increasing number of blows
Effect of Energy on Soil Compaction
Increasing compaction energy
Lower OWC and higher dry density
Higher
Energy
Dry Density
In the field
increasing compaction energy = increasing number of passes or reducing lift depth
ZAV
In the lab
increasing compaction energy = increasing number of blows
Water Content

12. Field Soil Compaction
Because of the differences between lab and field compaction methods, the maximum dry density in the field may reach 90% to 95%.
Dry Density
ZAV
gd max
95% gd max
Moisture
Content
(OMC)

13. Example: gwet gdry = % Gs gw gZAV = Wc 1+
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:
Volume of
Proctor Mold
(ft3)
1/30
Weight of wet soil in the mold (lb)
3.88
4.09
4.23
4.28
4.24
4.19
Water Content (%) 12 14 16 18 20 22
Volume of
Mold
(ft3)
1/30
Weight of wet soil in the mold (lb)
3.88
4.09
4.23
4.28
4.24
4.19
Water Content
(%) 12 14 16 18 20 22
Wet Unit Weight
(lb/ft3)
116.4
122.7
126.9
128.4
127.2
125.7
Dry Unit Weight
103.9
107.6
109.4
108.8
106.0
103.0
gdry =
gwet Wc
100 % 1+
Gs gw
gZAV = 1+ Wc Gs Sr

14. gdry max
Optimum
Water
Content

15. Checking Soil Density in the Field:
1- Sand Cone (ASTM D )
2- Balloon Dens meter
The same as the sand cone, except a rubber
balloon is used to determine the volume of the hole
3- Nuclear Density (ASTM D )
A small hole (6" x 6" deep) is dug in the compacted material to be tested.  The soil is removed and weighed, then dried and weighed again to determine its moisture content.  A soil's moisture is figured as a percentage.  The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device.  The dry weight of the soil removed is divided by the volume of sand needed to fill the hole.  This gives us the density of the compacted soil in lbs per cubic foot.  This density is compared to the maximum Proctor density obtained earlier, which gives us the relative density of the soil that was just compacted.
Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content.  The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission).  The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit.  Dense soil absorbs more radiation than loose soil and the readings reflect overall density.  Water content (ASTM D3017) can also be read, all within a few minutes. 

16. Nuclear Density
Sand Cone

17. Compaction Specifications:
Compaction performance parameters are given on a construction project in one of two ways:
1- Method Specification
detailed instructions specify machine type, lift depths, number of passes, machine speed and moisture content.  A "recipe" is given as part of the job specifications to accomplish the compaction needed. 
2- End-result Specification
Only final compaction requirements are specified (95% modified or standard Proctor). This method, gives the contractor much more flexibility in determining the best, most economical method of meeting the required specs.