Pavement Design

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• Pavement Design

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• I. Pavement Design
• A. Overview

Degree of curvature
Principal cause of pavement failure shown
abovenot the blacktop
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• I. Pavement Design
• B. California Bearing Ratio (CBR)

How to build a road!
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• I. 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.

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• I. Pavement Design
• B. California Bearing Ratio (CBR)
• 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.

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• I. Pavement Design
• B. California Bearing Ratio (CBR)
• 3. The Test

Take load readings at penetrations of
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
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4. Plot the Data
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5. Determine the percent of compacted crushed
stone values for the 0.1 and 0.2 penetration.
The Gold Standard for CBR for 0.1 of
penetration, 1000 psi for 0.2 of penetration,
1500 psi
Example above for 0.1 of penetration, 220
psi for 0.2 of penetration, 300 psi
The standard material for this test is crushed
California limestone
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5. Determine the percent of compacted crushed
stone values for the 0.1 and 0.2 penetration.
Example psi CBR Standard psi
220 psi .22, or 22 1000 psi
300 psi .20, or 20 1500 psi
CBR of material 22
The Gold Standard for CBR for 0.1 of
penetration, 1000 psi for 0.2 of penetration,
1500 psi
Example above for 0.1 of penetration, 220
psi for 0.2 of penetration, 300 psi
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5. Determine the percent of compacted crushed
stone values for the 0.1 and 0.2 penetration.
Example psi CBR Standard psi
220 psi .22, or 22 1000 psi
300 psi .20, or 20 1500 psi
CBR of material 22
The Gold Standard for CBR for 0.1 of
penetration, 1000 psi for 0.2 of penetration,
1500 psi
Example above for 0.1 of penetration, 220
psi for 0.2 of penetration, 300 psi

• Use 0.1 of penetration, unless 0.2 is the
  greater value.
• If so, then rerun the test, taking the higher of
  the two values from this second trial

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5. Determine the percent of compacted crushed
stone values for the 0.1 and 0.2 penetration.

• In General
• 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,
• Moist sand may have a CBR of 10.
• High quality crushed rock has a CBR over 80.
• The standard material for this test is crushed
  California
• limestone which has a value of 100.

Example psi CBR Standard psi
220 psi .22, or 22 1000 psi
300 psi .20, or 20 1500 psi
CBR of material 22, or 22
The Gold Standard for CBR for 0.1 of
penetration, 1000 psi for 0.2 of penetration,
1500 psi
Example above for 0.1 of penetration, 220
psi for 0.2 of penetration, 300 psi
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Potential Corrections to the Stress-Penetration
Curves
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• I. Pavement Design
• C. The Mechanics of the Design

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• I. Pavement Design
• C. The Mechanics of the Design
• Determine
• The CBR values of the subgrade
• The type of use expected (runways vs. taxiways)

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• I. Pavement Design
• C. The Mechanics of the Design
• 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

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• I. 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
• Dont break the bank
• Use less inexpensive CBR materials when allowed
  while not shortchanging the projects integrity

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• I. 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)?

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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
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CBR subbase of 8, Taxiway, and wheel load of
40,000 lb
23 inches
23 inches of total earth material and pavement
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• I. 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)
• What is the optimal pavement thickness (wearing
  surface)?
• What is the optimal CBR value of upper 6 inches?

23 inches
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• I. 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)
• What is the optimal pavement thickness (wearing
  surface)?
• What is the optimal CBR value of upper 6 inches?

Wearing Surface 0-15k.....2 gt15k-40k..3 gt40k-
55k..4 gt55k-70k..5 gt70k..6
Wheel Pound Loads CBR Value 15,000 or less 50
15k-40k 65 40k-70k 80 70k-150k 80
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• I. 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)
• What is the optimal pavement thickness (wearing
  surface)?
• What is the optimal CBR value of upper 6 inches?

23 inches
3 inches
6 inches of CBR 65/80
Wearing Surface 0-15k.....2 gt15k-40k..3 gt40k-
55k..4 gt55k-70k..5 gt70k..6
Wheel Pound Loads CBR Value 15,000 or less 50
gt15k-40k 65 gt40k-70k 80 gt70k-150k 80
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3
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• 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)
• What is the optimal pavement thickness (wearing
  surface)?
• What is the optimal CBR value of upper 6 inches?

CBR 80
23 inches
3 inches
6 inches of CBR 65/80
Wearing Surface 0-15k.....2 gt15k-40k..3 gt40k-
55k..4 gt55k-70k..5 gt70k..6
Wheel Pound Loads CBR Value 15,000 or less 50
gt15k-40k 65 gt40k-70k 80 gt70k-150k 80
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3
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• 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)
• What is the optimal pavement thickness (wearing
  surface)?
• What is the optimal CBR value of upper 6 inches?
• What can we use for the remainder of thickness?

CBR 80
23 inches
3 inches
6 inches of CBR 65/80
Wearing Surface 0-15k.....2 gt15k-40k..3 gt40k-
55k..4 gt55k-70k..5 gt70k..6
Wheel Pound Loads CBR Value 15,000 or less 50
gt15k-40k 65 gt40k-70k 80 gt70k-150k 80
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Need 9 minimum thickness
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CBR 27 for remainder of base (14)
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Given Same CBR subgrade as before Materials
available of CBR30, 80 Determine Optimal
thickness of each layer while minimizing costs
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Given Same CBR subgrade as before Materials
available of CBR30, 80 Determine Optimal
thickness of each layer while minimizing costs
CBR of 30 needs minimum of 9 of pavement courses
above it.
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Given Same CBR subgrade as before Materials
available of CBR30, 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
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Given Same CBR subgrade as before Materials
available of CBR30, 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
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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 30,
80 Determine Optimal thickness of each layer
while minimizing costs

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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 30,
80 Determine Optimal thickness of each layer
while minimizing costs
3 of wearing surface 6 of CBR 80 in upper 6
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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 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
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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 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
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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 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
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Another Example Given Same CBR subgrade as
before Materials available of CBR15, 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
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Your turn. Subbase of CBR7, 50,000 lb loads
for a taxiway CBR materials available 80, 30,
15 Design the pavement with attention paid to
optimizing costs and stability
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Your turn. Sub base of CBR7, 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 CBR80 CBR 30 of 7 CBR
15 of 11
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Homework Subbase of CBR15, 70,000 lb loads for
a runway CBR materials available 80, 40,
20 Design the pavement with attention paid to
optimizing costs and stability