Pavement Design

In March of 1981, the International Civil Aviation Organization (ICAO) announced a single worldwide standard for the expression of airfield pavement strength and aircraft pavement load intensity –the Aircraft Classification Number – Pavement Classification Number (ACN-PCN) system (ICAO 1999). In addition to directing that runways, taxiways and aprons should have sufficient strength to withstand the load of the heaviest aircraft expected to operate at a given airport (ICAO 1999), ICAO directed that member States should adopt the ACN-PCN system for all airports that serve international traffic. In order for a uniform standard to be applied to the expression of aircraft load capability, ICAO adopted the Westergaard center-load case condition for rigid pavement applications, and CBR method for flexible pavement (Gervais et al. 2004). The ACN-PCN for an aircraft was calculated using the CBR methodology at a fixed 10,000 coverages to failure. Application of a wheel load on the critical pavement section was called a coverage. For the design of CC1, the FAA CBR design procedure contained in AC 150/5320-6C was initially used to design flexible and rigid pavements. For the case of B777, the FAA method did not support triple tandem gear. Therefore, the DC-10 aircraft (which had similar loads as the B777) was used as the design aircraft with 50% increase in passes to account for the additional two wheels in the triple tandem. However, it was found that this method was conservative as compared to LET and FEM methods. Therefore, in designing the CC1, LEDFAA 1.2 was used with 10,000 passes to failure, 4-wheel loading gear configuration and 45,000 lbs. wheel load. The core of LEDFAA 1.2 program was JULEA, which was a layered elastic computational program. Since prior full scale testing programs were performed at coverage levels of 3,000 or less, higher coverage levels were selected to better quantify failure mechanisms.

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