# Soil Compaction by h1st7S4

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```									                     Soil Compaction and
Pavement Design

pneumatic rubber-tired roller   vibratory steel-wheeled roller

Sheeps foot roller
I.      Overview of Soil Compaction
A.      Compaction (concept): the densification
of soil by removal of air.
•       Requires mechanical energy
•       Densification increases with help of
water

“water acts as softening agent and allows
soil particles to slip over one another,
thereby increasing the packing factor”
•    There is an optimal moisture content that
maximizes densification, or maximum density
– “optimum moisture, maximum density”
Unit weight has units of
density * gravity
I. Overview
B. Factors Affecting Compaction
1. Grain size
2. Grain shape
3. Sorting
II. Laboratory Methods for Determining OM and MD

The Proctor Test (after Ralph R. Proctor, 1933)
II. Laboratory Methods for Determining OM and MD

The Proctor Test (after Ralph R. Proctor, 1933)
II. The Method

The Proctor Test (after Ralph R. Proctor, 1933)
II. The Method

The Proctor Test (after Ralph R. Proctor, 1933)
Unit weight has units of
density * gravity
III. Terms to “Reckon with”
Porosity: = volume of voids              n = Vv
volume total of material         Vt

Moisture Content: = weight of water      w = Ww
weight of dry soil       Ws

Unit Weight: (φw) = weight of soil and water     φw = Ws+Ww = Ww
(moist)            volume total of soil               Vt     Vt
(lbs/ft3)

Unit Weight (φd) : = unit weight (wet)           (φd) = φw
(dry)              1 + (moisture content /100)       1+(w/100)
(lbs/ft3)
IV. Field Methods of Determining if OM &
MD are achieved
A. Sand Cone Method
IV. Field Methods of Determining if OM &
MD have been achieved
A. Sand Cone Method

Unit Weight: = weight of soil and water   γw = Ws+Ww = Ww
(moist)       volume total of soil            Vt      Vt

Moisture Content: = weight of water       w = Ww
weight of soil            Ws
IV. Field Methods of Determining if OM &
MD have been achieved
B. Nuclear Density Meter
V. Pavement Design
A. Overview
Degree of curvature

“Principal cause of pavement failure shown above—not the blacktop”
V. Pavement Design
B. California Bearing Ratio (CBR)

V. Pavement Design
B. California Bearing Ratio (CBR)
1. The California bearing ratio (CBR) is a
penetration test for evaluation of the mechanical
was developed by the California Department of
Transportation.
V. Pavement Design
B. California Bearing Ratio (CBR)
1. The California bearing ratio (CBR) is a penetration test
for evaluation of the mechanical strength of road
subgrades and basecourses. It was developed by the
California Department of Transportation.

2. The test is performed by measuring the
pressure required to penetrate a soil sample
with a plunger of standard area. The measured
pressure is then divided by the pressure
required to achieve an equal penetration on a
standard crushed rock material.
V. Pavement Design
B. California Bearing Ratio (CBR)
3. “The Test”

“the result”
0.025” ……………70 psi
0.05”……………...115 psi
0.1”……………….220 psi
0.2”……………….300 psi
0.4”……………….320 psi

6” mold
“Achieve OM &MD”

Penetrations of 0.05” per minute
4. Plot the Data

350

300

250

200

150

100

50

0
0   0.05   0.1   0.15      0.2      0.25       0.3   0.35   0.4   0.45
Penetration (inches)
5. Determine the percent of compacted crushed stone values for the 0.1 and 0.2
penetration.
350

300

250

200

150

100

50

0
0   0.05    0.1   0.15      0.2      0.25       0.3   0.35   0.4   0.45
Penetration (inches)

“The Gold Standard” for CBR                                            Example above:
for 0.1” of penetration, 1000 psi                                      for 0.1” of penetration, 220 psi
for 0.2” of penetration, 1500 psi                                      for 0.2” of penetration, 300 psi
The standard material for this test is
crushed California limestone
5. Determine the percent of compacted crushed stone values for the 0.1 and 0.2
penetration.
350

300
Example psi = CBR
Standard psi                                       250

200

220 psi = .22, or 22%
150
1000 psi
300 psi = .20, or 20%                                100

1500 psi                                              50

CBR of material = 22%                                  0
0   0.05    0.1   0.15      0.2      0.25       0.3   0.35   0.4   0.45
Penetration (inches)

“The Gold Standard” for CBR                                           Example above:
for 0.1” of penetration, 1000 psi                                     for 0.1” of penetration, 220 psi
for 0.2’ of penetration, 1500 psi                                     for 0.2” of penetration, 300 psi
5. Determine the percent of compacted crushed stone values for the 0.1 and 0.2
penetration.

Example psi = CBR          In General:
Standard psi               •The harder the surface, the higher the CBR rating.
•A CBR of 3 equates to tilled farmland,
•A CBR of 4.75 equates to turf or moist clay,
220 psi = .22, or 22%        •Moist sand may have a CBR of 10.
1000 psi                     •High quality crushed rock has a CBR over 80.
300 psi = .20, or 20%        •The standard material for this test is crushed California
1500 psi                        limestone which has a value of 100.

CBR of material = 22%,
or “22”

“The Gold Standard” for CBR                Example above:
for 0.1” of penetration, 1000 psi          for 0.1” of penetration, 220 psi
for 0.2’ of penetration, 1500 psi          for 0.2” of penetration, 300 psi
Potential Corrections to the
Stress-Penetration Curves

350

300

250

200

150

100

50

0
0   0.05   0.1   0.15      0.2      0.25       0.3   0.35   0.4   0.45
Penetration (inches)
V. Pavement Design
C. The Mechanics of the Design
V. Pavement Design
C. The Mechanics of the Design
1. Determine
•   The CBR values of the subgrade
•   The type of use expected (runways vs.
taxiways)
V. Pavement Design
C. The Mechanics of the Design
1. Determine
•   The CBR values of the subgrade
•   The type of use expected (runways vs.
taxiways)
•   The expected wheel load during service
•   Types of CBR materials available for the
construction
V. Pavement Design
C. The Mechanics of the Design
2. Primary Goals
•   Total strength of each layer only as good as what is
beneath it
•   Therefore, must meet minimum thickness requirements
•   “Don’t break the bank”
•   Use less inexpensive CBR materials when allowed while
not shortchanging the project’s integrity
V. Pavement Design
C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)?
“ a point on the curve for a
given CBR material represents
the minimum thickness of
pavement courses that will
reside above it, in order to
maintain stability
CBR subbase of 8,
of 40,000 lb
23 inches
V. Pavement Design
C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)
23 inches
What is the optimal pavement thickness (wearing surface)?
What is the optimal CBR value of upper 6 inches?
V. Pavement Design
C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)
23 inches
What is the optimal pavement thickness (wearing surface)?
What is the optimal CBR value of upper 6 inches?

Wheel Pound Loads      CBR Value            Wearing Surface
15,000 or less        50                   0-15k…….....2”
15k-40k               65                   >15k-40k…..3”
40k-70k               80                   >40k-55k…..4”
70k-150k              80+                  >55k-70k…..5”
>70k……..…6”
V. Pavement Design
C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)
23 inches
What is the optimal pavement thickness (wearing surface)? 3 inches
What is the optimal CBR value of upper 6 inches? 6 inches of CBR 65/80

Wheel Pound Loads      CBR Value             Wearing Surface
15,000 or less        50                    0-15k…….....2”
>15k-40k              65                    >15k-40k…..3”
>40k-70k              80                    >40k-55k…..4”
>70k-150k             80+                   >55k-70k…..5”
>70k……..…6”
3”                                          6”
V. Pavement Design                   CBR = 80

C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)
23 inches
What is the optimal pavement thickness (wearing surface)? 3 inches
What is the optimal CBR value of upper 6 inches? 6 inches of CBR 65/80

Wheel Pound Loads         CBR Value              Wearing Surface
15,000 or less           50                     0-15k…….....2”
>15k-40k                 65                     >15k-40k…..3”
>40k-70k                 80                     >40k-55k…..4”
>70k-150k                80+                    >55k-70k…..5”
>70k……..…6”
3”                                          6”
V. Pavement Design                   CBR = 80

C. The Mechanics of the Design
3. An example
A compacted subgrade has a CBR value of 8. What is the minimum
pavement thickness if it is to support a taxiway pavement
designed to support a 80,000 lb airplane (40,000 wheel load)
23 inches
What is the optimal pavement thickness (wearing surface)? 3 inches
What is the optimal CBR value of upper 6 inches? 6 inches of CBR 65/80
What can we use for the remainder of thickness?
Wheel Pound Loads         CBR Value              Wearing Surface
15,000 or less           50                     0-15k…….....2”
>15k-40k                 65                     >15k-40k…..3”
>40k-70k                 80                     >40k-55k…..4”
>70k-150k                80+                    >55k-70k…..5”
>70k……..…6”
Need = 9” minimum
thickness
CBR = 27 for
remainder of base
(14”)
before

Materials available of:
CBR=30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
before

Materials available of:
CBR=30, 80

Determine:
Optimal thickness of each
layer while minimizing costs

CBR of 30 needs minimum of 9”
of pavement courses above it.
before

Materials available of:
CBR=30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
CBR of 30 needs minimum of 9”
of pavement courses above it.
3” of wearing surface
6” of CBR 80 in upper 6”
before

Materials available of:
CBR=30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
CBR of 30 needs minimum of 9”
of pavement courses above it.
3” of wearing surface
6” of CBR 80 in upper 6”
14” of CBR 30
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
3” of wearing surface
6” of CBR 80 in upper 6”
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
3” of wearing surface
6” of CBR 80 in upper 6”

A CBR of 15 requires X” above it
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
3” of wearing surface
6” of CBR 80 in upper 6”

A CBR of 15 requires 15” above it
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
3” of wearing surface
6” of CBR 80 in upper 6”

A CBR of 15 requires 15” above it
A CBR of 30 requires X” above it
Another Example:
before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
layer while minimizing costs
3” of wearing surface
6” of CBR 80 in upper 6”

A CBR of 15 requires 15” above it
A CBR of 30 requires 9” above it

Subbase of CBR=7,
50,000 lb loads for a taxiway
CBR materials available: 80, 30, 15

Design the pavement with attention paid to optimizing costs and stability

Sub base of CBR=7,
50,000 lb loads for a taxiway
CBR materials available: 80, 30, 15

Design the pavement with attention paid to optimizing
costs and stability
Solution:
Total Thickness: 28”
Wearing Surface Thickness: 4”
Upper 6” of CBR=80
CBR 30 of 7”
CBR 15 of 11”
Homework:

Subbase of CBR=15,
70,000 lb loads for a runway
CBR materials available: 80, 40, 20

Design the pavement with attention paid to optimizing costs and stability

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