Design Principles

Although airfield pavement design is a speciality in its own right there are no text books on the subject. General pavement texts such as Principles of Pavement Design (Witzak and Yoder1) and others 2,3, describe the basic principles of pavement design and give some explanation of the use of specific airfield pavement design methods; otherwise the only source of information are the airfield pavement design and evaluation methods themselves.

Although airfield pavement structural behaviour and failure mechanisms are similar to roads, there are some major differences in
loadings and performance requirements including:

• The magnitude of the loading, up to 30 tonnes per wheel.
• The configuration of the loading, with up to 28 wheels in an undercarriage, with wheels in groups of up to 8 on a main wheel gear.
• Tyre pressures, which reach 15 bar (220psi, 1.52MPa) on civil aircraft and 31 bar (450 psi, 3.10MPa) on military aircraft.
• The number of loadings, generally less than 1 million in the design life, rather than potentially several hundred million for major roads.
• Requirements for pavement durability. Loose material can cause what is generally known as Foreign Object Damage (FOD), in particular to jet engines, with potentially catastrophic consequences for aircraft.

Aircraft with widely differing weights and undercarriage configurations can have similar damaging effects on a pavement, or aircraft with similar weights but different undercarriage configurations can have very different damaging effects. The implication for airfield pavement design is that there are two unknowns, the load and the number of load repetitions, whereas in road design the load is basically fixed, as a standard axle, and only the number of load repetitions varies.

This problem has led to significant developments in airfield pavement engineering aimed at equating damaging effects of varying loads and undercarriage arrangements, such as airfield-pavement classification systems and mixed traffic analysis or cumulative damage techniques.