Pavement Design Al-Balqa’ Applied University Faculty of Engineering Technology Department of Civil Engineering M. Kharabsheh Fall 2013-2014 8/2/2018 CEE 320 Steve Muench

Empirical 1993 AASHTO Flexible Equation 1993 AASHTO Rigid Equation

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)

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.

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

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

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

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

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

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

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

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

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.

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