1. Geotechnics 1 (BFC 21702)
SOIL COMPACTION

2. 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

3. 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

4. Soil Compaction in the Lab:
Hammer – 4.5 kg
Hammer – 2.5 kg
Volume of the mold
= cm3
Equipments for compaction test

5. Soil Compaction in the Lab: 1- Standard Proctor Test
2- Modified Proctor Test
2.5 kg
4.5 kg
304.8 mm
457.2 mm
Standard Proctor Test
Modified Proctor Test

6. Soil Compaction in the Lab:
Standard Proctor Test
Modified Proctor Test
Diameter of mold
101.6 mm
Volume of mold
944 cm3
Weight of hammer
2.5 kg
4.54 kg
Height of hammer drop
304.8 mm
457.2 mm
Number of blows per layer 25
Number of layers 3 5
Energy of compaction
600 kNm/m3
2700 kNm/m3
Soil to be used
Portion passing no.4 (4.57 mm) sieve. May be used if 20% or less by weight is retained on no.4 sieve.

7. Soil Compaction in the Lab:
Video

8. Analysis from Soil Compaction test in the Lab:
1. From the test, the density or the unit weight can be determined; or
2. The moisture content for each test is determined in the laboratory. So: or
3. Then the graph of dry unit weight or dry density versus moisture content can be plotted.

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%
2.5 kg hammer
gd max 3
H = mm 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  600 kNm/m3
Zero Air Void Curve
Sr < 100%
gd max
Compaction
Curve for Modified
Proctor
Energy  2700 kNm/m3
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. Factor Affecting Compaction
Soil Type
Compaction Effort
1- particle size distribution
2- shape of the soil grain
3- Specific gravity of soil solids
4- Amount & type of clay minerals
1- Energy applied on the soil

12. 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

13. 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)

14. 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
(cm3)
943.3
Weight of wet soil in the mold (kg)
1.76
1.86
1.92
1.95
1.93
1.90
Water Content (%) 12 14 16 18 20 22
Volume of
Mold
(cm3)
943.3
Weight of wet soil in the mold (kN)
17.27
18.25
18.84
19.13
18.93
18.64
Water Content
(%) 12 14 16 18 20 22
Wet Unit Weight
(kN/m3)
18.3
19.3
20.0
20.3
20.1
19.8
Dry Unit Weight
16.34
16.93
17.24
17.20
16.75
16.23
gdry =
gwet Wc
100 % 1+
Gs gw
gZAV = 1+ Wc Gs Sr

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

17. COMPACTION Roller Compactors
Smooth wheel rollers can create vertical vibration during compaction. They are suitable for proof-rolling subgrades and for finishing construction of fills with sandy or clayey soils.
Pneumatic rubber-tired rollers produce a combination of pressure and kneading action. They can be used for sandy and clayey soil compaction.

18. COMPACTION Roller Compactors
Sheepsfoot rollers are most effective in compacting cohesive soils. During compaction, the initial passes compact the lower portion of a lift. Later, the middle and top of the lift are compacted.
Vibratory rollers are efficient in compacting granular soils. Vibrators can be attached to smooth wheel, pneumatic, or sheepsfoot rollers to produce vibrations.

19. COMPACTION Roller Compactors
Grid rollers consists of drums covered with heavy steel grid, creating high contact pressure while preventing excessive shear deformation. They are suitable for weathered rock (such as sandstone), well-graded sand, soft rocks and stony soils.
Impact rollers consists of a noncircular mass which is towed along the ground, exerting high impact force. They are suitable for natural ground and fill.

20. COMPACTION Tampers, Rammers and Plate Compactors
Vibrating tampers or rammers and vibrating plate compactors are used in confined areas such as on backfill in trenches, around pipes, and behind retaining walls and bridge abutments.

21. Towing speed of the compactor Number of roller passes
COMPACTION
Compaction in field depends on several factors:
Type of compactor
Soil type
Moisture content
Lift thickness
Towing speed of the compactor
Number of roller passes

22. Specifications for the compaction of a given soil in the field:
The contractor is required to achieve a relative compaction of 90% or more on the basis of a specific laboratory test.
Relative compaction, RC =

23. 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. 

24. Nuclear Density
Sand Cone

25. Example

26. Solution

27. Solution

28. Solution

29. Example 2

30. Solution

31. Solution