22 - subgrade characterization
TRANSCRIPT
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Subgrade Characterization
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CIVL 3137 2
Pavement Design Factors
Changes over Time
Subgrade Support ProvidedSeasonal Changes in Subgrade Support
Magnitude of Wheel Loads
Wheel Loads Applied to Pavement
Type of Wheel Loads (Single or Tandem Axles)
Number of Wheel Load Applications
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CIVL 3137 3
Pavement Design Factors
Changes over Time
Subgrade Support ProvidedSeasonal Changes in Subgrade Support
Magnitude of Wheel Loads
Wheel Loads Applied to Pavement
Type of Wheel Loads (Single or Tandem Axles)
Number of Wheel Load Applications
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CIVL 3137 4
Subgrade Support
Modulus of Subgrade Reaction (k)
Hveem Resistance Value (R)
Resilient Modulus (MR)
California Bearing Ratio (CBR)
AASHTO Group Index
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CBR Inventor
Source: http://gsl.erdc.usace.army.mil/gl-history/images/gl_img_25r.jpg
O. James Porter
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CIVL 3137 7
California Bearing Ratio
Source: http://www.archive.official-documents.co.uk/document/ha/dmrb/index.htm
Sample soakedfor 4 days prior
to testing
(Area = 3 in2)
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CIVL 3137 9
California Bearing Ratio
Source: http://www.southerntesting.co.uk/insitutesting.html
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CIVL 3137 10
California Bearing Ratio
Penetration (inches)
0.0 0.1 0.2 0.3 0.4 0.5
9000
0
100
90
80
70
60
50
40
30
20
10
6000
3000
Load
(pou
nds)
100
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CIVL 3137 11
California Bearing Ratio3500
3000
Load
(lb)
2500
2000
1500
1000
500
0
Piston Penetration (in)
0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
2050CBR 100 683000
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CIVL 3137 12
Typical CBR Values
Description of Material CBR Well-graded crushed aggregates 100 Well-graded natural gravels 80 Silty gravel or silty, sandy gravel 40-80 Well-graded sands, gravelly sands 20-50 Clayey gravel or sandy, clayey gravel 20-40 Silty or clayey sands 10-40 Fine clean sands 10-20 Lean (low-plasticity) clays, sandy clays 5-15 Silts, sandy silts 5-15 Organic silts, lean organic clays 4-8 Fat (high-plasticity) clays 3-5
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CIVL 3137 13
Rigid Pavements
Spring constant = modulus of subgrade reaction (K)
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CIVL 3137 14
Modulus of Subgrade Reaction
30 in.
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CIVL 3137 15
Modulus of Subgrade Reaction
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CIVL 3137 16
Modulus of Subgrade Reaction
K
1
PRES
SURE
(PSI
)
DEFLECTION (IN)
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CIVL 3137 17
Typical K Values
Description of Material K (psi/in) Well-graded gravel 300-450 Silty sands 300-400 Well-graded sands, gravelly sands 200-400 Fine sand (e.g. beach sand) 150-350 Clayey sands 150-350 Fat (high-plasticity) clays 40-225Lean (low-plasticity) clays, sandy clays 25-225 Silts, sandy silts 25-200
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CIVL 3137 18
Resilient Modulus
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Resilient Modulus
CIVL 3137 19
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CIVL 3137 21
Resilient ModulusStr
ess
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CIVL 3137 22
Typical MR Values
Description of Material MR (psi)
Crushed Stone
Sandy Subgrade
Silty Subgrade
Clayey Subgrade
20,000 – 50,000
15,000 – 30,000
5000 – 20,000
5000 – 15,000
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CIVL 3137 23