This paper applies statistical and probabilistic methods to the design of pavements, using the existing aashto equations. The major purpose for applying such methods was to assess the variation of thepavement geometry as a function of the variabilities of design factors. A linear first-order approximation was applied on the aashto pavement design equation to determine the effect of the variation of traffic and soil support value on the variation of structural number for flexible pavement and the effect of the variation of traffic andconcrete flexural strength on the variation of slab thickness for rigid pavements. The mean and variance equations for the pavement geometry were derived by using taylor's series expansion about the mean. Nomographic solutions of these equations are provided, which wouldprove helpful in practical applications. The final design thicknessof the pavement for a specific service life and design parameters variability is obtained by combining the nomographic solutions with the least cost concept, thereby satisfying economy, performance and statistical design requirements. Examples to illustrate the use of this technique in the design of both flexible and rigid pavements are presented. This paper appears in transportation research record no. 1227, Rigid and flexible pavement design and analysis: unbound granular materials, tire pressures, backcalculation, and design methods.
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