Probabilistic and Reliability Analysis of the California Bearing Ratio (CBR) Design Method for Flexible Airfield Pavements.

The California Bearing Ratio CBR design method for flexible airfield pavements was analyzed using a probabilistic approach. The design parameters considered were the load P or the equivalent single-wheel load, the sub-grade CBR, the tire contact area A, and the pavement total thickness t. The expected value and variance of the dependent variable performance factor, alpha which is logarithmically related to the number of passes to failure were estimated by using the Taylor series expansion and the Rosenblueth method. Differences in computed results between the two methods were found to be small, although the derivation of the expressions for Taylor series expansion was very complicated. A procedure was developed to estimate the reliability of the designed pavement system based on known variabilities of design parameters. Results of the reliability analysis indicate that prediction of pavement performance is most influenced by variations of pavement thickness t and is least influenced by variations of tire contact are A. The effects of variations of wheel load P and subgrade CBR are identical. The weighting factors for parameters t, CBR, P, and A, in general, are approximately 1, 0.34, 0.34, and 0.01, respectively Table 3.