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# Review of Compaction Principles by zhangyun

VIEWS: 71 PAGES: 82

• pg 1
```									    Objectives
 Be able to use basic    Be able to perform
volume weight            basic compaction test
equations                (LAB EXERCISE)
 Understand principal
 plot compaction data
of soil compaction.      and evaluate for
 Explain how the          accuracy
compaction test is      Understand procedure
used in design and       for Atterberg Limit
quality control          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.
 Compactiontests 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
State Diagram
Dry Density, pcf

100 %
saturation
curve

Water content, %
State Diagram
Dry Density, pcf

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
At this water content, energy has
a large effect on compacted
density
Dry Density, pcf

10 passes of
equipment
4 passes of
equipment
3 passes of
equipment
2 passes of
equipment

1 pass of
equipment
Water content, %
At this point, the sample has had
most of its air driven out by the
compaction
Dry Density, pcf

10 passes of
equipment

100 %
saturation line

Water content, %
At a lower water content, energy
has little effect on the compacted
density of a clay soil
Dry Density, pcf

10 passes of
4 passes of
equipment of
3 passes
equipment
equipment
2 passes of
equipment
1 pass of
equipment
Water content, %
Compacting at low water contents

 Atlow 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
At a very high water content,
energy has little effect on the
compacted density of a clay
soil because the water is
Dry Density, pcf

incompressible and takes the
applied force without
densifying the soil

This results in a term            103passes of
4 passes of
called pumping                     equipmentof
equipment
2 passes
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
Effect of Water Content
Dry density, pcf

99.0
pcf
Sample 1 compacted at 12 %
water – Dry Density is 99.0 pcf

12 %              Water content, %
Effect of Water Content

Sample 2 compacted at
Dry density, pcf

14 % water – Dry Density
104.5                is 104.5 pcf
pcf

14 %         Water content, %
Effect of Water Content
Dry density, pcf

105.5
pcf
Sample 3
compacted at
16 % water –
Dry Density
is 105.5 pcf

Water content, %   16 %
Effect of Water Content
Dry density, pcf

Sample 4
compacted at
18 % water –
Dry Density
is 98.5 pcf
98.5
pcf

Water content, %       18 %
Effect of Water Content @ constant
energy
Dry density, pcf

Maximum
dry density,
pcf

Optimum water
content, %
Water content, %
Now, perform the same test at a
different (Higher energy) on the soil
10 passes of
sheepsfoot
roller
Dry density, pcf

4 passes of
sheepsfoot
Water content, %      roller
Effect of Soil Type on Curves

Plastic Clay Soils have Low
Values of Maximum Dry
Dry density, pcf

80-95
Density
pcf

Water content, %
Effect of Soil Type on Curves

Plastic Clay Soils have high
values for optimum water
Dry density, pcf

content (20-40 %)

20-40 %

Water content, %
Effect of Soil Type on Curves

Plastic Clay Soils have a Flat
Curve for Lower Energies
Dry density, pcf

Density

Water content, %
Effect of Soil Type on Curves
115-135
pcf
Dry density, pcf

Sandy Soils with Lower PI’s
have High Values of
Maximum Dry Density

Water content, %
Effect of Soil Type on Curves
Dry density, pcf

Sandy Soils with Lower PI’s have
Low Values of Optimum Water
Content

8-15 %

Water content, %
Effect of Soil Type on Curves
Dry density, pcf

Sandy Soils have a Steep Curve
– Short distance from plastic to
liquid states of consistency

Water content, %
Lower PI –
Summary                            Sandier Soils in
110-135                       this Region

Intermediate PI
Dry density, pcf

95-120                           Soils in this
Region
Higher PI –
Clayey Soils in
this Region
75-95

Water content, %
Lower PI –
Summary      Sandier Soils in
this Region

Intermediate PI
Higher PI –
Soils in this
Clayey Soils in
Region
this Region
Dry density, pcf

8-14     12-20    20-40
Water content, %
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 #
hammer
 Uses  5.5 pound
hammer
 dropped 12 inches
12”drop
 mold filled in 3 lifts
 25 blows of hammer
per lift                 3 lifts
 Total energy is
12,400 ft-lbs/ft3
Modified Proctor Compaction Test
Summary
10 #
hammer
 Uses  10 pound
hammer
 dropped 12 inches
18”drop
 mold filled in 5 lifts
 25 blows of hammer
per lift                 5 lifts
 Total energy is
12,400 ft-lbs/ft3
Proctor Compaction Test Summary
Standard molds are used
 Several
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
Standard molds are used
 Several
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              D1557A
– D698B              D1557B
– D698C              D1557C
Proctor Compaction Test Summary

   Prepare 4 to 5
specimens at
increasing water
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          Cured soil
procedures
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
Class Problem
Mold wt = 4.26 #, Mold Vol. = 0.03314 ft3
Class Problem

Calculate   Moist density, dry density
Plotcurve 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 gd and calculate wsat%
Assumed dry density = 105
assumed Gs = 2.70
pcf      Unit wt. water = 62.4
100 % Saturation
Curve
95 % Saturation
Curve
wsat(%) = 22.1(%)

75 % Saturation
Curve
Zero Air Voids Curve
Plotted Class Problem
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
100 % Saturation
Curve

95 %
Saturation
Curve
75 %
Saturation
Curve
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

2.7 %
2.1 % 2.7 %

Are points about two percent apart ?
Evaluating compaction test

Are two points below and 2 above
optimum ?
Review of Compaction
Optimum w% = 21.0 
Optimum water content
about 80 % saturated        % sat = 21.0÷23.6=89%
water content ? -
Acceptable range is    102.5 pcf

75-95
Plotted Class Problem
wopt/wsat =
21.0/23.6 = 89 % 

wsat @ 102.5 pcf =
(62.4/102.5 - 1/2.68) * 100 = 23.6 %
Review of Compaction
Wet side parallel to
saturation curve at 
90 % saturation ? % Sat = 24.3 ÷ 26.4 =
92.0 %

gd, pcf
Check a point on wet side at
98 pcf, w % on curve is
24.3%

w, %
Plotted Class Problem

wopt/wsat =
24.3/26.6 = 91 % 

wsat @ 98.0 pcf =
(62.4/98.0 - 1/2.70) * 100 = 26.6 %
Review of Compaction

Evaluating Compaction Tests
Typical value for fine-grained soils
compared to Navdocks equations

gdmax = 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
gdmax = 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
 Soilsare 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 re-
tested 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
Compaction
Tests as
Used in
Design of an
Earth Fill
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

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