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Subgrade Characterization

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Sub grade Characterization is important in design of slabs on grade

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  • Subgrade Characterization

  • CIVL 3137 28

    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

  • CIVL 3137 29

    Subgrade Support

    Modulus of Subgrade Reaction (k)

    Hveem Resistance Value (R)

    Resilient Modulus (MR)

    California Bearing Ratio (CBR)

    AASHTO Group Index

  • CBR Inventor

    Source: http://gsl.erdc.usace.army.mil/gl-history/images/gl_img_25r.jpg

    O. James Porter

  • CIVL 3137 32

    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)

  • CIVL 3137 34

    California Bearing Ratio

    Source: http://www.southerntesting.co.uk/insitutesting.html

  • CIVL 3137 35

    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

    L

    o

    a

    d

    (

    p

    o

    u

    n

    d

    s

    )

    100

  • CIVL 3137 36

    California Bearing Ratio3500

    3000

    L

    o

    a

    d

    (

    l

    b

    )

    2500

    2000

    1500

    1000

    500

    0

    PistonPenetration(in)

    0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

    2050CBR 100 683000

  • CIVL 3137 37

    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

  • CIVL 3137 38

    Rigid Pavements

    Spring constant = modulus of subgrade reaction (K)

  • CIVL 3137 39

    Modulus of Subgrade Reaction

    30 in.

  • CIVL 3137 40

    Modulus of Subgrade Reaction

  • CIVL 3137 41

    Modulus of Subgrade Reaction

    K

    1

    P

    R

    E

    S

    S

    U

    R

    E

    (

    P

    S

    I

    )

    DEFLECTION (IN)

  • CIVL 3137 42

    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

  • CIVL 3137 43

    Resilient Modulus

  • Resilient Modulus

    CIVL 3137 44

  • CIVL 3137 46

    Resilient ModulusS

    t

    r

    e

    s

    s

  • CIVL 3137 47

    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