Determining Moisture-Unit Weight Relations of Soil
(Compaction Test)
Dr. U.P. Nawagamuwa
Department of Civil Engineering
University of Moratuwa
Dept of Civil Eng, University of Moratuwa
Class Outlines
Standard Proctor Compaction Test
Effect of Compaction Energy
Modified Proctor Compaction Test
Specification for Field Compaction
Dept of Civil Eng, University of Moratuwa
Compaction
In construction of highway embankments,
earth dams and many other engineering
structures, loose soils must be compacted to
improve their strength by increasing their unit
weight
Compaction - Densification of soil by removing
air voids using mechanical equipment
The degree of compaction is measured in
terms of its dry unit weight
Dept of Civil Eng, University of Moratuwa
Compaction Effect
Air
Water Air
Water
Solid Solid
Loose soil Compacted soil
Dept of Civil Eng, University of Moratuwa
Compaction Advantages
As compaction increases, the following
occurs:
Increase soil strength
Increase bearing capacity
Decrease potential for settlement
Control undesirable volume changes
Reduction in hydraulic conductivity
Dept of Civil Eng, University of Moratuwa
Effect of Water on Compaction
In soils, compaction is a function of water content
Water added to the soil during compaction acts as a
softening agent on the soil particles
Consider 0% moisture - Only compact so much
Add a little water - compacts better
A little more water - a little better compaction
Even more water – Soil begins to flow
What is better compaction?
The dry unit weight (gd) increases as the moisture
content increases TO A POINT
Beyond a certain moisture content, any increase in
moisture content tends to reduce the dry unit weight
Dept of Civil Eng, University of Moratuwa
Compaction Curve
Compaction curve
plotted gd vs. w
The peak of the curve is
the Maximum
Compaction (gd max) at
Optimum Moisture
Content (wopt )
g Gs g w
gd or g d
1
w (%) 1 e
100
Dept of Civil Eng, University of Moratuwa
Standard Proctor Compaction Test
The standard was originally developed to simulate
field compaction in the lab
Purpose: Find the optimum moisture content at which
the maximum dry unit weight is attained
ASTM D 698
Equipments;
Standard Proctor
3
1/30 ft mold
5.5 lb hammer
12” drop
3 layers of soil
25 blows / layer
Dept of Civil Eng, University of Moratuwa
Compaction - Lab Equipment
Dept of Civil Eng, University of Moratuwa
Procedure
1. Obtain 10 lbs of soil passing No. 4 sieve
2. Record the weight of the Proctor mold without the base and
the (collar) extension, the volume of which is 1/30 ft3.
3. Assemble the compaction apparatus.
4. Place the soil in the mold in 3 layers and compact using 25
well distributed blows of the Proctor hammer.
5. Detach the collar without disturbing the soil inside the mold
6. Remove the base and determine the weight of the mold and
compacted soil.
7. Remove the compacted soil from the mold and take a sample
(20-30 grams) of soil and find the moisture content
8. Place the remainder of the molded soil into the pan, break it
down, and thoroughly remix it with the other soil, plus 100
additional grams of water.
Dept of Civil Eng, University of Moratuwa
Compaction - Procedure
4
5
Dept of Civil Eng, University of Moratuwa
Results
Plot of dry unit
weight vs moisture
content
Find gd and wopt
(max)
Plot Zero-Air-Void
unit weight
(only S=100%)
Dept of Civil Eng, University of Moratuwa
Standard Proctor Test Modified Proctor Test
Dept of Civil Eng, University of Moratuwa
Effect of Compaction Energy
With the development of heavy rollers and their uses
in field compaction, the Standard Proctor Test was
modified to better represent field compaction
As the compaction effort increases,
the maximum dry unit weight of compaction increase
The optimum moisture content decreases to some
extend
Compaction energy per unit volume
E
No. of blows per layer No. of layers weight of hammer height of drops
Volume of mold
Dept of Civil Eng, University of Moratuwa
Effect of Compaction Energy (Cont.)
Dept of Civil Eng, University of Moratuwa
Modified Proctor Test
The modified was developed to simulate
larger compaction effort for more serious
loads and bigger equipment
ASTM D 698
Modified Proctor
1/30 ft3 mold
10 lb hammer
18” drop
5 layers of soil
25 blows / layer
Dept of Civil Eng, University of Moratuwa
Specification for Field Compaction
Specifications will refer to % Relative Compaction
Relative to what?
Proctor Test – standard or modified
% Relative Compaction
g d field
R% 100 R ~ (90 – 100%)
g d max lab
If R > 100 % use Modified Proctor Test
Soil will be compacted to 98% relative compaction as
compared to a standard proctor test, ASTM D-698
The soil moisture content will be ± 2% of optimum.
Dept of Civil Eng, University of Moratuwa
Specification for Field Compaction
98% means the soil in the field should be
98% of the lab result
For example, if the peak of the curve is at
100 pcf and 22% moisture
The field compaction must be at least 98 pcf
and within the stated moisture range (20
~24%)
Dept of Civil Eng, University of Moratuwa
Measurement of Field
Compaction
Most common
methods are
Core-cutter Method
Sand Cone method
Rubber Balloon method
Nuclear Method
Dept of Civil Eng, University of Moratuwa
Sand Cone Method
Dept of Civil Eng, University of Moratuwa
Quantity
Test Steps
Obtaining the unit weight of the sand used
1. Weight of Proctor mold, W1 4.178 kg
2. Weight of proctor mold + Sand, W2 5.609 kg
3. Volume of the mold, V1 0.00095 m3
4. Dry unit weight, gd (sand) = (W2 - W1) / V1 1506 kg/m3
Calibration cone
5. Weight of plastic Gallon+Cone+Sand (before use), W3 5.466 kg
6. Weight of plastic Gallon+Cone+Sand (after use), W4 3.755 kg
7. Weight of the sand to fill the cone, Wc = W4- W3 1.711 kg
Results from field tests
8. Weight of plastic Gallon+Cone+Sand (before use), W5 7.387 kg
9. Weight of plastic Gallon+Cone+Sand (after use), W6 3.919 kg
10. Volume of hole, V2 = (W5-W6-Wc)/ gd (sand) 0.00117m3
11.Weight of evaporating dish, W7 0.507 kg
12. Weight of evaporating dish + wet soil from the field, W8 2.334 kg
13. Weight of evaporating dish + dry soil after 24hrs, W9 2.251 kg
14. Moist unit weight of the soil in the field, gt (in-situ soil) = (W8 -
1561 kg/m3
W 7) / V 2
15. Water content in the field, w(%)= (W8 - W9) / (W9- W7)*100 4.76%
16. Dry unit weight in the field, gd (in-situ soil)=gt (Row 14)] / [1+
1490 kg/m3
w(%) / 100]
Conversion factors (Unit weight):
Dept of Civil Eng, University of Moratuwa
1000 kg/m3 = 9.81 KN/m3 = 62.4 lb/ft3
Thank you!
Dept of Civil Eng, University of Moratuwa
