ABSTRACT
ABSTRACT: The ACN/PCN method has been adopted by the ICAO as the standard for reporting airfield pavement bearing strength. For a more conservative evaluation and design approach, the mean value minus one standard deviation (or the so-called 85% confidence level) may be used for obtaining evaluation or design inputs in general (AC 150/5320-6D). Nevertheless, it was found that this procedure was not based on sound statistical principles especially when the probability distribution of the population is almost always unknown. Consequently, the concepts of random sampling, central limit theorem, and confidence intervals for hypothesis testing were adopted. It was proposed that a single representative design input for the entire runway pavement be determined by the lower limit of 95% confidence level to derive a more consistent and repeatable PCN value. A case study was conducted to illustrate the potential problems of the existing ACN/PCN procedures and the benefits of the proposed revisions.
