AIRPORT PLANNING MANUAL 7. PAVEMENTDATA 7.1. GENERALINFORMATION Pavement is defined as a structure consisting of one or more layers of processed materials. Theprimary function of a pavement is to distribute concentrated loads so that the supporting capacity of the subgrade soil is not exceeded. The subgrade soil is defined as the material on which the pavement rests, whether embankment or excavation. Several methods for design of airport pavements have been developed that differ considerably in their approach. The design methods are derived from observation of pavements in service or experimental pavements. Thus, the reliability of any method is proportional to the amount of experimental verification behind the method, and all methods require a considerable amount of common sense and judgment on the part of the engineer who applies them. Abrief description of the following pavement charts will be helpful in their use for airport planning. Each aircraft configuration is depicted with a minimum range of five loads imposed on the main landing gear to aid in the interpolation between the discrete values shown. The tire pressure used for the aircraft charts will produce the recommended tire deflection with the aircraft loaded to its maximum ramp weight andwith center of gravity position. The tire pressure, where specifically designated in tables and charts, are values obtained under loaded conditions as certified for commercial use. This section is presented as follows: • The basic data on the landing gear footprint configuration, maximum design ramp loads, and tire sizes and pressures. • The maximum pavement loads for certain critical conditions at the tire-ground interfaces. • A chart in order to determine the loads throughout the stability limits of the aircraft at rest on the pavement. Pavement requirements for commercial aircraft are customarily derived from the static analysis of loads imposed on the main landing gear struts. These main landing gear loads are used to enter the pavement design charts which follow, interpolating load values where necessary. • The flexible pavement curves prepared in accordance with the US Army Corps of Engineers Design Method and the LCN Method. • The rigid pavement design curves in accordance with the Portland Cement Association Design Method and the LCN Method. • The aircraft ACN values for flexible and rigid pavements. EFFECTIVITY: ALL Section 7 Page 7-1 Dec08/03 b-apm1346