Objectives

1
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)

2
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

3
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)

4
Principle of compaction

• Theory developed by R.R. Proctor in 1930s in
  California
• Three Factors determine the density that results
  from soil compaction

5
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

6
State Diagram
Dry Density, pcf
100 saturation curve
Water content,
7
State Diagram
Dry Density, pcf
Water content,
8
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

9
At this water content, energy has a large effect
on compacted density
Dry Density, pcf
Water content,
10
At this point, the sample has had most of its air
driven out by the compaction
Dry Density, pcf
100 saturation line
Water content,
11
At a lower water content, energy has little
effect on the compacted density of a clay soil
Dry Density, pcf
Water content,
12
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

13
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
Dry Density, pcf
This results in a term called pumping
Water content,
14
Compacting Very Wet Soil
At this point, few air pockets remain
compaction forces are carried by water in soil
which is incompressible
15
Water has Zero Shear Strength
16
Water has Zero Shear Strength
17
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

18
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,
19
Effect of Water Content
Dry density, pcf
Sample 2 compacted at 14 water Dry Density is
104.5 pcf
104.5pcf
14
Water content,
20
Effect of Water Content
Dry density, pcf
105.5pcf
Sample 3 compacted at 16 water Dry Density is
105.5 pcf
16
Water content,
21
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
22
Effect of Water Content _at_ constant energy
Dry density, pcf
Maximum dry density, pcf
Optimum water content,
Water content,
23
Now, perform the same test at a different (Higher
energy) on the soil
Dry density, pcf
10 passes of sheepsfoot roller
4 passes of sheepsfoot roller
Water content,
24
Effect of Soil Type on Curves
Dry density, pcf
Plastic Clay Soils have Low Values of Maximum Dry
Density
Water content,
25
Effect of Soil Type on Curves
Dry density, pcf
Water content,
26
Effect of Soil Type on Curves
Dry density, pcf
Plastic Clay Soils have a Flat Curve for Lower
Energies Density
Water content,
27
Effect of Soil Type on Curves
Dry density, pcf
115-135 pcf
Sandy Soils with Lower PIs have High Values of
Maximum Dry Density
Water content,
28
Effect of Soil Type on Curves
Dry density, pcf
Sandy Soils with Lower PIs have Low Values of
Optimum Water Content
8-15
Water content,
29
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,
30
Summary
Dry density, pcf
Water content,
31
Summary
Dry density, pcf
Intermediate PI Soils in this Region
12-20
Water content,
32
Family of Curves (Covered Later)
33
Family of Curves
Zero air voids curve not parallel to line of
optimums at upper end
gd, dry density, pcf
Line of Optimums
water content,
34
Proctors 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.

35
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.

36
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

37
Standard Proctor Compaction Test Summary
5.5 hammer

• Uses 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

12drop
3 lifts
38
Modified Proctor Compaction Test Summary
10 hammer

• Uses 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

18drop
5 lifts
39
Proctor Compaction Test Summary

• Several Standard molds are used depending on
  maximum particle size in sample
• 4diameter mold (1/30 ft3) used for soils with
  low gravel contents
• Method A for soils with lt 20 gravel
• Method B for soils with gt 20 gravel and lt 20
  larger than 3/8

40
Proctor Compaction Test Summary

• Several Standard molds are used depending on
  maximum particle size in sample
• 6diameter 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

41
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 3/4in diameter gravels
• ASTM Compaction Test Methods are
• D698A D1557A
• D698B D1557B
• D698C D1557C

42
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.

43
Proctor Compaction Test Summary
Hammer

• Then, compact each sample into a steel mold with
  standard procedures

Cured soil
Compaction mold
44
Proctor Compaction Test Summary

• Then, strike off excess soil so the mold has a
  known volume of soil.

45
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.
  Dont 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

46
Class Problem

• Calculate Moist density, dry density

47
Class Problem
Mold wt 4.26 , Mold Vol. 0.03314 ft3
48
Class Problem

• Calculate Moist density, dry density
• Plot curve of dry density versus water content
• Determine Maximum dry density and optimum water
  content

49
Set Up Plot Form SCS-352
110

5 pounds
90
50
Set Up Plot Form SCS-352
Make each vertical division equal to 1 percent
water content
51
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

52
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

53
Compaction Problem
Zero air void equation Assume 3 values of gd and
calculate wsat
54
wsat() 22.1()
55
Zero Air Voids Curve
56
Plotted Class Problem
57
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

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59
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 ?

60
Compaction Problem
Other given information LL 47, PI 30,
classified as CL soil Gs 2.68
61
Evaluating compaction test
Are points about two percent apart ?
62
Evaluating compaction test
Are two points below and 2 above optimum ?
63
Review of Compaction

• Optimum water content about 80 saturated water
  content ? - Acceptable range is 75-95

102.5 pcf
64
Plotted Class Problem
wopt/wsat 21.0/23.6 89 ?
wsat _at_ 102.5 pcf (62.4/102.5 - 1/2.68) 100
23.6
65
Review of Compaction

• Wet side parallel to saturation curve at ? 90
  saturation ?

Sat 24.3 26.4 92.0
gd, pcf
w,
66
Plotted Class Problem
67
Review of Compaction

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

?dmax 130.3 - 0.82 LL 0.3PIwopt 6.77
0.43 LL - 0.21 PI
68
Review of Compaction

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

?dmax 130.3 - 0.82 47 0.330
100.8 pcfOK - test value was 102.5 pcfwopt
6.77 0.43 47 - 0.21 30 19.6 OK
Test value was 21.0
69
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

70
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.

71
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.

72
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.

73
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

74
Compaction Tests as Used in Design of an Earth
Fill
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76
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

77
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

78
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.

79
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

80
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

81
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?

82
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