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Pavement Design

Pavement Design. Al-Balqa’ Applied University Faculty of Engineering Technology Department of Civil Engineering M. Kharabsheh Fall 2013-2014. CEE 320 Steve Muench. Empirical . 1993 AASHTO Flexible Equation 1993 AASHTO Rigid Equation. Terms – Flexible.

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Pavement Design

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  1. Pavement Design Al-Balqa’ Applied University Faculty of Engineering Technology Department of Civil Engineering M. Kharabsheh Fall 2013-2014 CEE 320Steve Muench

  2. Empirical • 1993 AASHTO Flexible Equation • 1993 AASHTO Rigid Equation

  3. Terms – Flexible • The ZR and So variables account for reliability • W18 (loading) • Predicted number of 80 kN (18,000 lb.) ESALs over the pavement’s life. • SN (structural number) • Abstract number expressing structural strength • SN = a1D1 + a2D2m2 + a3D3m3 + … • ΔPSI (change in present serviceability index) • Change in serviceability index over the useful pavement life • Typically from 1.5 to 3.0 • MR (subgrade resilient modulus) (Measure Soil Stiffness) • Typically from 3,000 to 30,000 psi (10,000 psi is good)

  4. Recommended Values of ZR and So Typical values of So used are 0.40 to 0.50 for flexible pavements and 0.35 to 0.40 for rigid pavements.

  5. Resilient Modulus MR • Typical values for fine-grained soils are 2,000 to 10,000 psi. • Typical values for course-grained soils are 10,000 to 20,000 psi. If resilient modulus results are not available, then use the following correlations: For fine-grained soils with a soaked CBR between 5 and 10 , use the following equation to correlate CBR to resilient modulus (MR): Design MR (psi) = 1,500 x CBR For non fine-grained soils with a soaked CBR greater than 10, use the following equation: MR = 3,000 x CBR 0.65

  6. Terms – Rigid • D (slab depth) • S’c (PCC modulus of rupture) • A measure of PCC flexural strength • Usually between 600 and 850 psi • Cd (drainage coefficient) • Relative loss of strength due to drainage characteristics and the total time it is exposed to near-saturated conditions • Usually taken as 1.0

  7. Drainage Coefficient Quality of Drainage Water Removal Within Excellent 2 hours Good 1 day Fair 1 week Poor 1 month Very Poor no drainage

  8. Terms – Rigid • J (load transfer coefficient) • Accounts for load transfer efficiency • Lower J-factors = better load transfer • Between 3.8 (undoweled JPCP) and 2.3 (CRCP with tied shoulders) • Ec (PCC elastic modulus) • 4,000,000 psi is a good estimate • k (modulus of subgrade reaction) • Estimates the support of the PCC slab by the underlying layers • Usually between 50 and 1000 psi/inch

  9. Mean Effective k-value (psi/inch) Typical Range – 50 to 500 Typical Value for Pavement Design 200 – 250 If the subgrade resilient modulus is known or obtained from the CBR, then use the following equation: k-value = MR / 19.4

  10. Reliability Reliability = P [Y > X] X = Probability distribution of stress(e.g., from loading, environment, etc.) Y = Probability distribution of strength(variations in construction, material, etc.) Probability Stress/Strength

  11. Typical PSI vs. Time p0 Serviceability (PSI) p0 - pt pt Time

  12. Subgrade Characterized by strength and/or stiffness California Bearing Ratio (CBR) Measures shearing resistance Units: percent Typical values: 0 to 20 Resilient Modulus (MR) Measures stress-strain relationship Units: psi or MPa Typical values: 3,000 to 40,000 psi

  13. Subgrade Some Typical Values MR

  14. Flexible Pavement Design for Highways (Nomograph to Solve for SN)

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