He also looks at the effects of repeated aircraft overload operations on pavements and the best approach to pavement evaluation and maintenance.
Pavements are normally designed for a mix of traffic and a
The strength rating of airport pavements is commonly thought of, in terms of conventional structural concepts in which limiting loads are determined, based on ultimate strength or failure criteria.
Pavements, however, do not generally experience a loss in serviceability from instantaneous structural failure, but rather from an increase in surface roughness or deterioration of the surface resulting from the accumulated effects of traffic.
Structural failure is most often
Analysis of the adequacy of a pavement requires that a rating be assigned which not only considers the significance of load
The rate of deterioration of a pavement will, of course, be increased by
The Aircraft Classification Number (ACN) – Pavement Classification Number (PCN) system is the means by which airport owners and operators regulate the use of their pavements and balance pavement strength and maintenance strategies in relation to revenue from landing fees, ACNs must be calculated using a fixed technical method and are intended to indicate the relative pavement damaging effect of each aircraft.
An aircraft’s ACN is fixed by its weight, its wheel layout and the
The ACN-PCN system functions in practice as a pavement management tool for airport owners, not to protect aircraft. An airport owner might allow a particular aircraft to use the airport, only, if it operates at a restricted weight, and/or at
Pavements can sustain some overload, that is, pavement ratings are not absolute. There may be good reason why overload operations should be approved. For instance, the design traffic is operating at less than design capacity and limited overload may not reduce the life of the pavement or, depending on the overload, may only marginally reduce the life of the pavement. This reduction in pavement life may be preferred to the alternative of refusing a desirable operation or having to strengthen the pavement for infrequent operations.
At some stage in the life cycle
Repeated overloads may lead to the following failure conditions:
It may also result in high pavement maintenance costs. Repeated overloads may lead to the following effects on aircraft operations:
Airport pavement evaluations are necessary to assess the ability of an existing pavement to support different types, weights, or volumes of aircraft traffic. They are also critical in assisting airport owners with making a decision with regard to the most applicable PCN and acceptable pavement overloads.
The load carrying capacity of existing bridges, culverts, storm water drains, and other structures should also be considered in these evaluations. Evaluations may be also necessary to determine the condition of existing pavements for use in the planning or design of improvements to the airport.
In Pavement Design, the task is to determine the pavement thickness (and composition) required to support a specified aircraft traffic scenario. The thickness is dependent upon the strength of the in-situ soil material (the
For a given
In Pavement Evaluation, the pavement thickness and composition are known, and the task is to determine the traffic that can operate on the pavement. Again, the traffic is defined, in terms of the allowable operations (operations per day, week, month or year) of a combination of aircraft types at a range of loads. Clearly, for pavement evaluation, there is an extensive range of possible results because there can be a multitude of combinations of aircraft types, loads and frequency of operation.
The challenge, therefore, is to be able to assess the relative damaging effect of any single aircraft type at a specific load and frequency of operation, and then to be able to determine the cumulative damage caused by any such combinations.