Soil Compaction by h1st7S4

VIEWS: 45 PAGES: 51

									                     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)

  “How to build a road!”
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.
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”

                                    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
4. Plot the Data

                             350


                             300


                             250
      Load on Piston (psi)




                             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




                               Load on Piston (psi)
                                                      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




                              Load on Piston (psi)
                                                     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
Load on Piston (psi)




                       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,
Taxiway, and wheel load
 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”)
Given: Same CBR subgrade as
 before

Materials available of:
CBR=30, 80

Determine:
Optimal thickness of each
 layer while minimizing costs
  Given: Same CBR subgrade as
   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.
  Given: Same CBR subgrade as
   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”
  Given: Same CBR subgrade as
   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:
Given: Same CBR subgrade as
 before

Materials available of:
CBR=15, 30, 80

Determine:
Optimal thickness of each
 layer while minimizing costs
 Another Example:
 Given: Same CBR subgrade as
  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:
 Given: Same CBR subgrade as
  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:
 Given: Same CBR subgrade as
  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:
 Given: Same CBR subgrade as
  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:
 Given: Same CBR subgrade as
  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
Your turn….

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
Your turn….

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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