A sensitivity study of 14 items added to the 1986 AASHTO Guide for Design of Pavement Structures indicated: (1) variations in percent reliability were most influential on the design EAL for the same pavement structure while (2) variations in standard deviations had minimal effects. (3) Resilient moduli for base and subbase materials are very dependent upon stress state (or bulk stress). (4) A method was developed to quantify the effect of drainage capabilities for various soils and its effect upon reduction in structural coefficients for base and subbase materials. (5) Literature review revealed 13 relationships to define soil stiffness. The 1986 Guide has two equations for subgrade resilient modulus that yield results differing by factors of 2 to 10. Caution in their use cannot be over emphasized. (6) A method to account for environmental changes in subgrade materials is included in the 1986 Guide. (6) Temperature effects upon asphaltic concrete stiffness are not included. Sensitivity studies showed that temperature effects on pavement stiffness and variations in Structural Number far overshadow variations in subgrade stiffness. (7) The amount of material pumped from under rigid pavements appears to be a function of the number of axles passing over the spot rather than the number of groups of axles. (8) Kentucky and AASHTO load equivalencies were compared for the same stream of truck traffic. Fatigue data from the AASHO Road Test were used to compare the Kentucky and AASHTO thickness designs for the same soil stiffness. (9) The inclusion of mechanistic principles in pavement design was evaluated and discussed. (10) A value of 3.1 is recommended for the load transfer coefficient, J, because trucks travel with their tires located at the pavement-shoulder joint. (11) Kentucky employs most of the recommended rehabilitation procedures, or has more sophisticated procedures for those not being used. In some cases, economics has ruled out one, or more, of these procedures. (12) Kentucky thickness design methods include low volume roads. (13) Life cycle costs and pavement management were not included in this study because they are subjects of individual studies currently in progress.
Digital Object Identifier
Southgate, Herbert F., "Sensitivity Study of 1986 AASHTO Guide for Design of Pavement Structures" (1991). Kentucky Transportation Center Research Report. 684.