Angeli Gamez models the turning maneuver of aircraft and its effect on near-surface airfield pavement responses

The Airport Cooperative Research Program is an industry-driven applied research program that develops practical and innovative solutions to problems faced by airport operations and facilities.

Particularly, the ACRP Graduate Research Award challenges graduate students to tackle applied research related to aviation systems.

Annually, ten recipients are competitively selected not only to provide the opportunity to collaborate with ACRP mentors but also to participate at the Transportation Research Board Annual Meeting by presenting their work and publishing in the Transportation Research Record. Angeli Gamez, a doctoral candidate, advised by Professor Imad L. Al-Qadi, was one of the recipients of the 2017–18 ACRP Graduate Research Award. She recently presented her work at the Airport/Aircraft Compatibility Meeting at the TRB Conference in Washington D.C.

Analogous to heavy trucks on highways, airplanes induce high loads onto airfield pavement structures. Design and maintenance activities must comply with significant standards not only to promote quality and reliability, but also to ensure the security and safety of all users. Airplane high trafficking, landing, and traversing accelerates pavement damage.

One significant distress observed in airports is slippage failure, as illustrated in Figure 1(a). This mainly occurs at locations experiencing high shear stresses; for example, turning and taxiway areas as well as within the runway at landing areas where tires tend to make first contact with the pavement. A recent instrumentation study at the Newark International Airport (2016) reported that slippage cracks and interfacial delamination were observed at areas under high braking and turning.

The heavy Airbus A-380 has been banned from some airports because of its potential to damage airfield pavement. To further investigate this phenomenon, numerical modeling of flexible airfield pavement was completed, considering an A-380 landing gear tire (Figure 1[b]) under turning conditions.

The main objective was to quantify the influence of the turning maneuver on pavement responses and potential damage. Two analysis schemes were implemented: (1) extracting critical strains at the bottom of the asphalt concrete layer and on the top of the subgrade, and (2) domain analysis, a newly developed approach by Al-Qadi team at Illinois Center for Transportation of the University of Illinois, who have been working on advanced modeling of pavement, tire and tire-pavement interaction for the past two decades.

In the first procedure, the two strain values align with two critical distresses considered in flexible airfield pavement design: bottom-up asphalt concrete fatigue cracking and subgrade rutting (resulting from surface depression). However, a recent study on highway pavements at ICT revealed that strains (extracted from a single point within the pavement) cannot capture the potential damage at near-surface. Given similar strain values, the potential damage would be indistinguishable despite a significant difference in tire loading conditions. In the second approach, domain analysis encapsulates the bulk pavement behavior—how the entire structure behaves in three dimensions; damage occurs in the areas and not at a pinpoint.

Moreover, current airfield pavement design protocol does not account for damage that may occur at near-surface, e.g., slippage cracks. Using domain analysis, the near-surface influence of the tire’s turning maneuver was captured effectively. The highlighted areas within Figure 2 depicts the clear consequence of an aircraft tire turning-maneuver on pavement responses.

The results of this study not only established an initial platform to directly link the realistic interaction of aircraft tire loading and pavement responses but also advocated that special attention to turning area design is needed to ensure safe use of airports.

Larry Goldstein, Senior Program of the ACRP GRA program, said, “This has been a very successful program designed to bring graduate students into the world of applied airport and aviation research. The level of expertise and commitment by students, panel members, and mentors has been a most rewarding experience.”

The researchers appreciate receiving the instrumentation data and help from our alumnus Navneet Garg of the Federal Aviation Administration; the guidance of Larry Goldstein,Dominique Pittenger, and Mary Sandy, who all served as panel members for this award; and Sarah Pauls who coordinated the technical communications throughout the work. This study used the Extreme Science and Engineering Discovery Environment, which is supported by National Science Foundation grant number ACI-1548562.