Transcript Review of Compaction Principles

Objectives
Be able to use basic
volume weight
equations
 Understand principal
of soil compaction.
 Explain how the
compaction test is
used in design and
quality control

Be able to perform
basic compaction test
(LAB EXERCISE)
 plot compaction data
and evaluate for
accuracy
 Understand procedure
for Atterberg Limit
Tests (LAB
EXERCISE)

Review of Compaction Principles
 Compaction
Tests are not suitable for
soils with more than 30 % by weight of
the sample being larger than a ¾”
sieve.
 Compaction
tests are not usually
performed on soils with 12 % or fewer
fines
Review of Compaction Principles
 Relative
Density testing is used for
clean sands and gravels – covered later
in class
 Standard Procedures for testing are
available for soils with some gravel
(less than the maximum allowable
content)
Principle of compaction
 Theory
developed by R.R. Proctor in
1930’s in California
 Three
Factors determine the density
that results from soil compaction
Proctor Developed Principle
Three
variables determine the
density of a compacted soil
– The energy used in compaction
– The water content of the soil
– The properties of the soil
Dry Density, pcf
State Diagram
100 %
saturation
curve
Water content, %
Dry Density, pcf
State Diagram
Water content, %
Energy Used in Compaction
 Assume
you have some clay soil that is
at a water content of 16 percent.
 Look at the effect different compaction
energy has on the density of the soil.
 Energy expressed as number of passes
of a sheepsfoot roller on a lift of soil
Dry Density, pcf
At this water content, energy has
a large effect on compacted
density
10 passes of
equipment
4 passes of
equipment
3 passes of
equipment
2 passes of
equipment
1 pass of
equipment
Water content, %
Dry Density, pcf
At this point, the sample has had
most of its air driven out by the
compaction
10 passes of
equipment
100 %
saturation line
Water content, %
Dry Density, pcf
At a lower water content, energy
has little effect on the compacted
density of a clay soil
10 passes of
43 passes
equipment
passes of
of
equipment
2equipment
passes of
equipment
1 pass of
equipment
Water content, %
Compacting at low water contents
 At
low water contents, insufficient
water is available to lubricate the
particles and allow them to be
rearranged into a dense structure.
 The
frictional resistance of dry
particles is high
Dry Density, pcf
At a very high water content,
energy has little effect on the
compacted density of a clay
soil because the water is
incompressible and takes the
applied force without
densifying the soil
This results in a term
called pumping
1043passes
passesof
of
equipment
2equipment
passes of
equipment
1 pass of
equipment
Water content, %
Compacting Very Wet Soil
At this point, few air
pockets remain –
compaction forces
are carried by water
in soil which is
incompressible
Water has Zero Shear Strength
Water has Zero Shear Strength
Effect of Water Content
 Now
examine the effect of just changing the
water content on a clay soil, using the same
energy each time the soil is compacted.
 For example, assume soil is spread and
compacted with 4 passes of a sheepsfoot
roller each time.
 Examine using State Diagram
Dry density, pcf
Effect of Water Content
99.0
pcf
Sample 1 compacted at 12 %
water – Dry Density is 99.0 pcf
12 %
Water content, %
Dry density, pcf
Effect of Water Content
Sample 2 compacted at
14 % water – Dry Density
is 104.5 pcf
104.5
pcf
14 %
Water content, %
Dry density, pcf
Effect of Water Content
105.5
pcf
Sample 3
compacted at
16 % water –
Dry Density
is 105.5 pcf
Water content, %
16 %
Dry density, pcf
Effect of Water Content
98.5
pcf
Sample 4
compacted at
18 % water –
Dry Density
is 98.5 pcf
Water content, %
18 %
Dry density, pcf
Effect of Water Content @ constant
energy
Maximum
dry density,
pcf
Optimum water
content, %
Water content, %
Now, perform the same test at a
different (Higher energy) on the soil
Dry density, pcf
10 passes of
sheepsfoot
roller
Water content, %
4 passes of
sheepsfoot
roller
Dry density, pcf
Effect of Soil Type on Curves
80-95
pcf
Plastic Clay Soils have Low
Values of Maximum Dry
Density
Water content, %
Dry density, pcf
Effect of Soil Type on Curves
Plastic Clay Soils have high
values for optimum water
content (20-40 %)
20-40 %
Water content, %
Dry density, pcf
Effect of Soil Type on Curves
Plastic Clay Soils have a Flat
Curve for Lower Energies
Density
Water content, %
Effect of Soil Type on Curves
Dry density, pcf
115-135
pcf
Sandy Soils with Lower PI’s
have High Values of
Maximum Dry Density
Water content, %
Dry density, pcf
Effect of Soil Type on Curves
Sandy Soils with Lower PI’s have
Low Values of Optimum Water
Content
8-15 %
Water content, %
Dry density, pcf
Effect of Soil Type on Curves
Sandy Soils have a Steep Curve
– Short distance from plastic to
liquid states of consistency
Water content, %
Lower PI –
Sandier Soils in
this Region
Summary
Dry density, pcf
110-135
95-120
Higher PI –
Clayey Soils in
this Region
75-95
Water content, %
Intermediate PI
Soils in this
Region
Dry density, pcf
Summary
Lower PI –
Sandier Soils in
this Region
Intermediate PI
Higher PI –
Soils Soils
in thisin
Clayey
thisRegion
Region
8-14
12-20
Water content, %
20-40
Family
of
Curves
(Covered
Later)
Family of Curves
Zero air voids curve
not parallel to line of
optimums at upper
end
Line of
Optimums
water content, %
Proctor’s principle of compaction
 Using
a standard energy, if a series of
specimens of a soil are compacted at
increasing water contents, the
resultant dry density of the
specimens will vary. The density
will increase to a peak value, then
decrease.
Principle of Compaction
 A plot
of the dry density versus the
water content from a compaction test
will be parabolic in shape.
 The peak of the curve is termed the
maximum dry density, and the water
content at which the peak occurs is the
optimum water content.
Standard Proctor Energies
Several
standard energies are used
for laboratory compaction tests
– Standard – 12,400 ft-lbs/ft3
– Modified – 56,000 ft-lbs/ft3
– California – 20,300 ft-lbs/ft3
Standard Proctor Compaction Test
Summary
5.5 pound
hammer
 dropped 12 inches
 mold filled in 3 lifts
 25 blows of hammer
per lift
 Total energy is
12,400 ft-lbs/ft3
5.5 #
hammer
 Uses
12”drop
3 lifts
Modified Proctor Compaction Test
Summary
10 pound
hammer
 dropped 12 inches
 mold filled in 5 lifts
 25 blows of hammer
per lift
 Total energy is
12,400 ft-lbs/ft3
10 #
hammer
 Uses
18”drop
5 lifts
Proctor Compaction Test Summary
 Several
Standard molds are used
depending on maximum particle size in
sample
– 4”diameter mold (1/30 ft3) used for soils
with low gravel contents
– Method A for soils with < 20 % gravel
– Method B for soils with > 20 % gravel
and < 20 % larger than 3/8”
Proctor Compaction Test Summary
 Several
Standard molds are used
depending on maximum particle size in
sample
– 6”diameter mold (1/13.33 ft3) used for
soils with significant gravel contents
– More than 20 % gravel larger than 3/8”
– Must have less than 30 % larger than 3/4”
Proctor Compaction Test Summary
 Standardized
tests are not available for soils
with more than 30 percent by weight of the
total sample being larger than 3/4”in
diameter gravels
 ASTM Compaction Test Methods are
– D698A
– D698B
– D698C
D1557A
D1557B
D1557C
Proctor Compaction Test Summary

Prepare 4 to 5
specimens at
increasing water
contents about 2 %
apart. Example prepared samples at
14, 16, 18, and 20
percent. Use range of
moistures based on
feel and experience.
Proctor Compaction Test Summary
Hammer

Then, compact
each sample
into a steel
mold with
standard
procedures
Cured soil
Compaction mold
Proctor Compaction Test Summary
 Then,
strike
off excess
soil so the
mold has a
known
volume of
soil.
Proctor Compaction Test Summary
For each sample, measure the weight and the
water content of the soil in the mold
 The mold volume and weight are
pre-measured. Don’t assume nominal volume of
1/30 ft3 or 1/13.33 ft3
 Calculate moist density
 Calculate dry density
 Plot dry density and water content for each point

Class Problem
 Calculate
Moist density, dry density
WeightMoist
 moist 
Volume _ Mold
 dry
 moist

w%
1
100
Class Problem
Mold wt = 4.26 #, Mold Vol. = 0.03314 ft3
Point Mold Moist Moist
Water
Dry
+Soil Soil Density Content Density
pcf
%
pcf
1
8.04
3.78
17.5
2
8.30
4.04
19.6
3
8.38
4.12
21.7
4
8.29
4.03
24.4
Class Problem
Calculate
Moist density, dry density
Plot
curve of dry density versus
water content
Determine
Maximum dry density
and optimum water content
Set Up Plot – Form SCS-352
110
5
pounds
90
{
Set Up Plot – Form SCS-352
Make each vertical division equal
to 1 percent water content
Class Problem
 Calculate
Moist density, dry density
 Plot curve of dry density versus water
content
 Determine Maximum dry density and
optimum water content
 Plot zero air voids ( 100 % saturation
curve assuming specific gravity = 2.68
Zero Air Voids Curve
 After
you plot a compaction test,
plotting a zero air voids curve is very
important. This curve is also called the
100 % saturation curve
 This curve shows for a range of dry
density values what the saturated water
content is for any given value
Compaction Problem
Zero air void equation
Assume 3 values of d and calculate wsat%
  water 1 
wsat (%)  
  x100
  dry Gs 
 w
1 
w sat (%)   
  100
 d Gs 
135
Assumed dry density = 105
assumed Gs = 2.70
pcf
Unit wt. water = 62.4
100 % Saturation
Curve
Dry Density, pcf
125
115
95 % Saturation
Curve
wsat(%) = 22.1(%)
105
95
75 % Saturation
Curve
85
10
12
14
16
18
20
22
24
26
Water Content, %
28
30
32
34
Zero Air Voids Curve
Dry Unit Weight
pcf
95
100
105
Saturated
Water %
Plotted Class Problem
105
104
Maximum dry
density = 102.5 pcf
103
zero air
voids
curve
Dry Density, pcf
102
101
100
99
98
optimum w % = 21.0
%
97
96
95
15
17
19
21
23
w%
25
27
29
Zero Air Voids Curve
 The
100 % saturation curve is used to
judge the reliability of the compaction
curve and of field measurements of
compacted soil density and water
content
 Compacted soils for NRCS
specifications are usually at a degree of
saturation of about 75 to 95 percent
135.0
100 % Saturation
Curve
Dry Density, pcf
125.0
115.0
95 %
Saturation
Curve
105.0
75 %
Saturation
Curve
95.0
85.0
5.0
10.0
15.0
20.0
25.0
Water Content, %
30.0
35.0
Review of Compaction
 Evaluating
Compaction Tests
– Standard requirements - spread in
water content about 2 % and at least
two points above and below optimum
– Typical shape - soil type ?
Compaction Problem
Other given information:
LL = 47, PI = 30,
classified as CL soil
Gs = 2.68
Evaluating compaction test
2.1 %
105
104
103
zero air
voids
curve
Dry Density, pcf
102
101
2.1 % 2.7 %
100
2.7 %
99
98
97
96
Are points about two percent apart ?
95
15
17
19
21
23
w%
25
27
29
Evaluating compaction test
2.1 %
105
104
103
102
Dry Density, pcf
zero air
voids
curve
2.1 %
101
100
99
2.7 %
98
2.1 %
97
Are two points below and 2 above
optimum ?
96
95
15
17
19
21
23
w%
25
27
29
Review of Compaction
Optimum water content
about 80 % saturated
water content ? Acceptable range is
75-95
Optimum w% = 21.0 
% sat = 21.0÷23.6=89%
102.5 pcf
  water 1 
wsat(%)  

 x100
Gs 
  dry
1 
 62.4
wsat (%)  

x100  23.6(%)

102.5 2.68
Plotted Class Problem
105
104
wopt/wsat =
21.0/23.6 = 89 % 
Maximum dry
density = 102.5 pcf
103
zero air
voids
curve
Dry Density, pcf
102
101
100
99
98
optimum w % = 21.0
%
97
wsat @ 102.5 pcf =
(62.4/102.5 - 1/2.68) * 100 = 23.6 %
96
95
15
17
19
21
23
w%
25
27
29
Review of Compaction
Wet side parallel to
saturation curve at 
90 % saturation ? % Sat = 24.3 ÷ 26.4 =
Check a point on wet side at
98 pcf, w % on curve is
24.3%
d, pcf
  water 1 
wsat (%)  
  x100
Gs 
  dry
92.0 %
1 
 62.4
wsat (%)  

x100  26.4(%)

 98.0 2.68
w, %
Plotted Class Problem
105
104
Maximum dry
density = 102.5 pcf
103
zero air
voids
curve
Dry Density, pcf
102
101
wopt/wsat =
24.3/26.6 = 91 % 
100
99
98
optimum w % = 21.0
%
97
wsat @ 98.0 pcf =
(62.4/98.0 - 1/2.70) * 100 = 26.6 %
96
95
15
17
19
21
23
w%
25
27
29
Review of Compaction
Evaluating Compaction Tests
Typical
value for fine-grained soils
compared to Navdocks equations
dmax = 130.3 - 0.82 *LL + 0.3*PI
wopt = 6.77 + 0.43 * LL - 0.21 * PI
Review of Compaction
Evaluating Compaction Tests
Typical
value for fine-grained soils
compared to Navdocks equations
dmax = 130.3 - 0.82 *47 + 0.3*30
= 100.8 pcf
OK - test value was 102.5 pcf
wopt = 6.77 + 0.43 * 47 - 0.21 * 30
= 19.6 %
OK Test value was 21.0 %
Purposes of compaction
 Soils
are compacted to improve the
engineering properties over those of
loosely placed soils.
 The engineering properties are affected
both by the density to which the soil is
compacted and the water content at
which it is compacted
Role of compaction tests
in earth fill projects
 Samples
are obtained in site investigation
and sent to laboratory for testing
 Soils are tested to determine reference
density - as well as other index properties
 Engineering properties are measured by
testing at a percentage of the reference test
density. For example, a shear test might be
performed at 95 percent of the Standard
Proctor maximum dry density of the soil.
Role of compaction tests
in earth fill projects

The engineering properties are used in analyses
to determine a suitable design

For example, the shear strength is used in a slope
stability analyses

If the engineering properties allow a satisfactory
design, then the degree of compaction is used in
a contract specification.
Role of compaction tests
in earth fill projects

If an unsatisfactory design results, the soil is retested at a different degree of compaction to
obtain better engineering properties

The design is re-analyzed and the process
repeated until a final satisfactory degree of
compaction is decided

Then the degree of compaction is used in a
contract specification.
Role of compaction tests
in earth fill projects

Quality control processes are used to ensure that
the earth fill is compacted to the degree of
compaction specified, within a range of specified
water contents

Field compaction tests are performed to assure
that the proper reference density is being used
Samples are obtained and submitted
to a laboratory for
compaction tests
index tests
Compaction
Tests as
Used in
Design of an
Earth Fill
A Preliminary degree of
compaction is assumed
e.g., 95 % STandard Proctor
Engineering Property
Tests are performed at
the preliminary design density
e.g., shear tests
Engineering Properties are used
in an analyses - e.g.,
slope stability analysis
If the Design is Satisfactory,
Contract specs are written
requiring the degree of compaction
needed for the properties
If the Design is not Satisfactory,
a different degree of compaction
is assumed, and more engineering
property tests are performed
Quality Control Tests
are performed during
construction to ensure that
the required density and water content are met
When a satisfactory design is achieved
for the tested degree of
compaction, specifications are written
Quality Control Tests
are performed during
construction to ensure that
the required density and water content are met
Example of Process
 Sample
obtained to determine suitability as
clay liner
 Sample Sent to Laboratory
 Laboratory performs Standard Proctor Test
 A Permeability Test is performed at 95 % of
maximum Standard Proctor Dry Density
Example of Process
 The
sample is remolded at 2 percent wet of
optimum (for this sample, 85 % saturated)
 The permeability test measures an
acceptably low permeability
 A recommendation is given to the field
office that compaction to this combination
of density and water content results in
acceptably low permeability
Example of Process
 During
construction, measurements of dry
density and water content are made during
construction.
 If the degree of compaction and percent
saturation are equal to or better than
specified, the liner is judged to have a low
permeability and is considered acceptable.
Class Problem 2
 A compaction
test measures a maximum
dry density of 104.0 pcf and an optimum
water content of 18.0 %. The soil has an
estimated Gs value of 2.68
 A contract requires compaction to 95 % of
maximum dry density at a water content
of optimum or greater
Class Problem 2
A field test measures a moist density of 126.3
pcf and a water content of 23.4 %
 Does the compacted fill meet the contract
requirement ?
 Use the values given for measured moist
density and water content, calculate the dry
density
 Assume a Gs value of 2.68 and compute a wsat
value

Class Problem
 Compare
the reported compaction water
content to theoretical saturated water content
 Compacted soils are commonly in the range of
75-95 percent saturated
 What do the results tell you about the
reliability of the field data?
 What would you look for to explain any
problems?
Conclusions of Class Problem
 The
measured data appears to have
problems.
 Possible errors are in the measurement of
the dry density, the water content, or the
specific gravity value used in computations
 Recommend investigating most probable
causes