1. Pavement Design Al-Balqa’ Applied University
Faculty of Engineering Technology
Department of Civil Engineering
M. Kharabsheh
Fall
8/2/2018
CEE 320 Steve 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
Functional Classification
Recommended Level of Reliability
Urban
Rural
Interstate and Other Freeways
85 – 99.9
80 – 99.9
Principal Arterials
80 – 99
75 – 95
Collectors
80 – 95
Local
50 – 80
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) Ec (PCC elastic modulus)
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] Probability Stress/Strength
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 California Bearing Ratio (CBR) Measures shearing resistance
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 Classification CBR MR (psi)
Typical Description
Good
≥ 10
20,000
Gravels, crushed stone and sandy soils. GW, GP, GM, SW, SP, SM soils are often in this category.
Fair
5 – 9
10,000
Clayey gravel and clayey sand, fine silt soils.  GM, GC, SM, SC soils are often in this category.
Poor
3 – 5
5,000
Fine silty sands, clays, silts, organic soils.  CL, CH, ML, MH, CM, OL, OH soils are often in this category.

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