Airfield Pavement Design Research Articles

Comparison of Design Thicknesses for Flexible Airfield Pavement Based on Agency Limiting Subgrade Strain Criteria

A newly developed mechanistically based design procedure for airfield hot-mix asphalt pavement is studied. The pavement performance is calculated in terms of critical strains on the basis of multilayer theory. Rutting failure criteria from the Asphalt Institute, Shell Oil, and the revised U.S. Army Engineer Waterways Experiment Station (USACE-WES) are used to calculate the thickness requirements necessary for a range of design input variables. The program has been implemented in ZAPRAM, an event-driven, user-friendly educational computer program that runs in the Excel 2007 environment, coupled with Visual Basic programming. Results of the design comparison indicate a significant difference between the three common airfield pavement design procedures used. Differences between the Asphalt Institute procedure and the revised USACE-WES procedure are relatively moderate for all design situations. The greatest deviation is found between the Shell Oil approach and the other two criteria. The design difference depends heavily on several major factors. An analysis of heavy aircraft (B-747) operating on a low-support subgrade foundation may yield pavement design differences of 2 to 3 ft of granular subbase material. A major effort to enhance the state of the art for airfield pavement design models is recommended.

Impact of Environmental Site Location and Groundwater Table Depth on Thickness of Flexible Airfield Pavements

This comprehensive sensitivity study of a newly developed computer code at Arizona State University incorporates the influence of environmental site factors and the groundwater table depth on flexible airfield pavement design and performance. The newly developed code, called ZAPRAM, is a mechanistically based pavement model based on limiting strain criteria. The completed study used the newly revised U.S. Army Corps of Engineers failure criteria for subgrade shear deformation. The experimental factorial conducted comprised three aircraft types, three levels of as-compacted (optimum) subgrade condition, two levels of design aircraft passes, and an environmental combination of six groundwater table depths and five environmentally different city locations. The methodology used in this study applied the same analytical method to achieve real-time environmental effects on unbound layer modulus as the new AASHTO Mechanistic–Empirical Pavement Design Guide. The results of this effort showed for the first time the quantitative impact of the significant effects of climatic conditions at the design site, coupled with the importance of the depth of the groundwater table, on the predicted design thicknesses. Significant cost savings appear to be quite reasonable by using the principles of unsaturated soil mechanics in the new airfield pavement design procedure in ZAPRAM.

Validation of a Three-Dimensional Finite Element Model using Airfield Pavement Multiple Wheel Load Responses

ABSTRACT Various highway vehicle axle/wheel arrangements and aircraft gear configurations adopted nowadays to accommodate increasing load levels impact flexible pavement response and performance in accordance with different multiple wheel loading scenarios. As the demand for heavier wheel loads and number of load applications continually increases, it is essential to properly characterize the nonlinear behavior of the pavement subgrade and unbound aggregate base/subbase layers. This paper focuses on the validation of a recently developed three-dimensional (3D) nonlinear finite element (FE) model using the measured responses of airfield flexible pavement test sections trafficked under 4-wheel and 6-wheel aircraft gear configurations. For this purpose, realistic nonlinear, stress-dependent pavement subgrade and base/subbase resilient modulus models were employed in a programmed User MATerial (UMAT) subroutine of the general purpose ABAQUSTM FE program. The predicted pavement responses matched closely with the displacements and stresses measured in the field and the FE model could be reasonably applied to the design of airfield pavements serving multiple wheel gear loads when the nonlinear pavement geomaterials were considered. In addition, comparisons made between the single wheel superposition and the full 3D loading results proved the need and importance of 3D FE nonlinear analyses of thinly surfaced flexible pavements to properly consider both the stress dependent modulus behavior and the implications of multiple wheel loads and their interaction.

Evaluation of the Use of Reclaimed Asphalt Pavement in Airfield HMA Pavements

This paper summarizes the literature review as well as the documented use and performance of airfield pavements that used reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA). A review of in-service airfield pavements with RAP-containing HMA mixes was conducted as part of this study. Two civilian airports and one military airport were identified as currently using RAP in the HMA surface course. The three airports are Logan International Airport (BOS), Griffin-Spalding County Airport (6A2), and Oceana Naval Air Station (NTU). Furthermore, the impact of RAP on the performance life of HMA airfield pavements on a large hub, small hub, and general aviation was evaluated using actual airport traffic mixes. The performance life analysis used the characteristics and mechanical properties of HMA mixes in the linear elastic airfield pavement design software (LEDFAA1.3) to compare the estimated performance life of HMA pavements with and without RAP materials. The documented research effort has recently been conducted as part of the Airfield Asphalt Pavement Technology Program, Project 05-06.

Effects of Temperature Curling on Airfield Rigid Pavement Responses

ABSTRACT Pavement response measurements were collected from an in-service concrete pavement at the Denver International Airport. The effect of temperature curling on the measured strain and deflection responses for a several aircraft and load locations was analyzed. Theoretical slab analyses were also performed to compare the combined temperature and load stresses with the stress range, calculated as the difference between the combined and temperature-only stresses. The theoretical stress analyses showed that combined stresses (total) due to load and temperature were significantly different than stress range. The total stresses were greatly affected by the temperature difference magnitude and the assumed temperature distribution type (linear or nonlinear), whereas stress range was not as sensitive to changes in the slab's temperature differential or temperature distribution type. The measured deflections, caused by moving aircraft gear loads, were affected by temperature differential at the transverse dummy joint and corner location for dual and dual tandem aircraft. Overall, the measured deflections at the interior and hinged longitudinal joint were not as sensitive to the slab's temperature differential. Aircraft gear weight was the most significant factor in the measured deflection magnitude, whereas the aircraft individual wheel load was most related to the measured tensile strain magnitude. The measured strain was more sensitive to temperature differential for dual wheel aircraft loading, while the strain-induced by the dual tandem aircraft was not very sensitive to the slab's temperature differential. The slab positions, where significant gaps existed between the slab and base, also showed a relationship between the measured responses and temperature differential. The theoretical analysis and measured field data suggested temperature curling can be directly and accurately accounted for in airfield rigid pavement design only if the key stress components leading to slab fatigue cracking (total stress, stress range or both) are determined from full-scale experimental testing.

Effects of Temperature Curling on Airfield Rigid Pavement Responses

ABSTRACT Pavement response measurements were collected from an in-service concrete pavement at the Denver International Airport. The effect of temperature curling on the measured strain and deflection responses for a several aircraft and load locations was analyzed. Theoretical slab analyses were also performed to compare the combined temperature and load stresses with the stress range, calculated as the difference between the combined and temperature-only stresses. The theoretical stress analyses showed that combined stresses (total) due to load and temperature were significantly different than stress range. The total stresses were greatly affected by the temperature difference magnitude and the assumed temperature distribution type (linear or nonlinear), whereas stress range was not as sensitive to changes in the slab's temperature differential or temperature distribution type. The measured deflections, caused by moving aircraft gear loads, were affected by temperature differential at the transverse dummy joint and corner location for dual and dual tandem aircraft. Overall, the measured deflections at the interior and hinged longitudinal joint were not as sensitive to the slab's temperature differential. Aircraft gear weight was the most significant factor in the measured deflection magnitude, whereas the aircraft individual wheel load was most related to the measured tensile strain magnitude. The measured strain was more sensitive to temperature differential for dual wheel aircraft loading, while the strain-induced by the dual tandem aircraft was not very sensitive to the slab's temperature differential. The slab positions, where significant gaps existed between the slab and base, also showed a relationship between the measured responses and temperature differential. The theoretical analysis and measured field data suggested temperature curling can be directly and accurately accounted for in airfield rigid pavement design only if the key stress components leading to slab fatigue cracking (total stress, stress range or both) are determined from full-scale experimental testing.

Alternative Aircraft Loading Index for Pavement Structural Analysis

The most common practical way to simplify the structural analysis of airfield pavements is the use of equivalent single wheel load models instead of the actual gear of the aircrafts. As the accuracy and reliability of these models strongly affects the design and evaluation of airfield pavements, there is considerable need to investigate both system approaches. The first one, which uses a constant value for the pressure while the radius is variable, is currently under use by the aircraft classification number-pavement classification number method of the International Civil Aviation Organization, but despite this fact it proved to be inadequate to express the aircraft loading in many situations. On the contrary, according to this study, the second model, which has a constant value for the radius while the pressure varies, is more reliable, and it can be an interesting alternative. Thus, based on this model, an aircraft loading index is introduced, which aims to be a simple and reliable factor for expressing the severity of the loading of the aircrafts and a utility for several matters related to the airfield pavement applications.

Reliability Design of Flexible Airfield Pavements: Elastic Layered Method

A design procedure was developed for layered elastic flexible airfield pavement systems in terms of probability and reliability. A user-friendly computer program, RELIFLEX, was prepared to carry out the computations. The Rosenblueth method is used to estimate the expected value and variance of the computed strains (dependent parameters) on the basis of the input mean values of independent parameters (i.e., aircraft load, layer thicknesses, and material moduli). RELIFLEX has the capability of considering the strain distribution to be normal, lognormal, or beta, and a capacity-demand analysis is included. Only normal distribution is presented. Environmental effects and the lack of fit of the prediction models are not considered in RELIFLEX. The relationships between the reliability level and the allowable strain repetition of the designed system, established using RELIFLEX, provide a decision-making tool for engineers to design pavement at the desired reliability level. For a desired reliability level of the design system, pavement thickness can be varied to agree with the designed coverage or the allowable coverage can be modified for a given pavement thickness.

Mechanistic Evaluation of Rigid Airfield Pavements

A structural deterioration relationship is developed using the U.S. Army Corps of Engineers accelerated traffic tests for plain concrete airfield pavements. The relationship predicts the performance of the rigid pavement in terms of the structural condition index from the pavement's Westergaard edge stresses, flexural strength, and number of load applications. The model is compared to other design criteria and unfailed test sections and gives reasonable agreement. The relationship between the structural condition index and the coverages at initial failure of the pavement is determined, and an alternative fatigue curve is suggested for use in the thickness design of rigid airfield pavements with joints capable of load transfer. The relationships developed only account for the tensile fatigue-loading-induced deterioration of the rigid airfield pavement. Actual in-service pavements will show additional deterioration because of other jointed rigid pavement distresses such as pumping, settlement or faulting, d...

A commentary on A guide to airfield pavement design and evaluation

This Paper provides a commentary on A guide to airfield pavement design and evaluation, published by PSA Airfields Branch, which updates design methodology and incorporates knowledge acquired since publication of its predecessor in 1971.

Structural Response of Partially Fibrous Concrete Beams

The inclusion of fibers into a matrix over only a partial thickness of the beam is regarded as partially fiber reinforcing a beam. This concept is fully invoked in the present investigation. A tensile strain enhancement factor, t, as determined by a direct tension test, forms a convenient engineering parameter that takes care of the influence of the aspect ratio and volume fraction of the given type of fiber. The appropriate thickness of the beam section to be reinforced with fibers is computed using the above parameter. Necessary analytical expressions were developed to compute the moment enhancement factor associated with different values of the parameter, t. The validity of the approach was experimentally demonstrated. Practically similar deflection patterns for fully and partially fibrous sections were observed. The applicability of the method developed in practical situations, such as the design of airfield and highway pavements with fiber concretes, is cited.

Middle East—Highway and airfield pavements

Problems in the design of highway and airfield pavements in the arid or semi-arid countries of the Middle East are concerned more with the detrimental effects of the environment on the completed pavement than with the capacity of the subgrade soil to carry the traffic loads. These problems occur even when pavements are constructed on soils which would be regarded as providing an excellent subgrade by Western European standards. In most Middle Eastern countries the soil conditions are such that the graded soil when compacted by traffic provides a good running surface for road vehicles or taxi-ing aircraft without any need for paving. Until quite recently many inter-city roads were unpaved, and propeller-driven and even jet aircraft operated successfully from unsurfaced runways (Fig. 1). Paving was required only when the intensity of road traffic reached the stage when ravelling of the road surface commenced with the consequent unpleasant ‘washboard’ effect. Similarly heavy trafficking on unsurfaced runways and taxiways resulted in ingestion of stones into aircraft engines and damage to wing surfaces. The silty and clayey soils of parts of Jordan, Iraq and Iran, and the silty sabkha soils fringing the Trucial Coast undergo appreciable softening during rainy weather. Hence pavings are provided where all-weather serviceability is required from highways or airfields. Also run-off from the semi-impervious crust on the desert surface during heavy rain causes washouts of unpaved roads, requiring the attention of a grader to backfill the erosion gullies and restore the running surface. However, when a decision is

Full-Depth Asphalt Airfield Pavements

A brief review is presented of the newly revised edition of The Asphalt Institute airfield pavement design manual, \IFull-Depth Asphalt Pavements for Air Carrier Airports (MS-11)\N. A new design procedure predicated upon multilayered elastic concepts is introduced. The method is based on the necessity for designing against two types of pavement distress: (1) Cracking in the asphalt layer due to fatigue; and (2) excessive deformation due to overstressing the subgrade. The design procedure is briefly described. The design method is based on the theory that a full-depth asphalt pavement is a multilayered elastic system and that the application of load to the pavement produces two critical elastic strains: (1)Horizontal tensile strain at the bottom of the asphalt concrete layer; and (2) vertical compressive strain at the top of the subgrade layer. Design criteria based on maximum allowable values for the strains are used in developing the design procedure. Influence and effects of materials and environmental factors are examined.

Use of Concentration Index for Pavement Design

The application of the concentration index to pavements is illustrated. The problem with the design of flexible airfield pavements under newly developed jumbo-jet aircraft, as represented by the Lockheed C-5A Galaxy and the Boeing 747, is examined. These aircraft are equipped with extremely large multiple-wheel landing gears. It is found that the CBR design equation can be used to evaluate the pavement performance under multiple-wheel gear assemblies when the equivalent single-wheel load is computed by the concentration index method. The concentration index is approximately independent of the load, gear configuration, and soil strength but varies with the depth.

Parameters of Rational Airfield Pavement Design System

IN RECENT YEARS THE COMPLEXITY OF THE AIRFIELD PAVEMENT SYSTEM AND ITS ENVIRONMENT HAS RESULTED IN CONTINUED EFFORTS TO UPGRADE DESIGN AND EVALUATION METHODS. TO HELP MEET THE RECOGNIZED NEED FOR MORE EFFICIENT AND COMPREHENSIVE MANAGEMENT OF AIRFIELD PAVEMENT DESIGN, AN AIRFIELD PAVEMENT SYSTEM MODEL, WHICH IS PRESENTED HEREIN, HAS BEEN DEVELOPED. THE AIRFIELD PAVEMENT SYSTEM MODEL INCORPORATES MORE DETAIL, EXPANDS CERTAIN ASPECTS OF THE SYSTEM, AND INCLUDES CONCEPTS RELATING SPECIFICALLY TO AIRFIELD PAVEMENTS. IN ADDITION, THIS PAPER INCLUDES RECOMMENDATIONS REGARDING PARAMETERS WHICH SHOULD BE CONSIDERED IMMEDIATELY IN ANY OPERATIONAL SYSTEM IN ORDER THAT A SIGNIFICANT BEGINNING CAN BE MADE TOWARD ESTABLISHING A TRULY USEFUL AIRFIELD PAVEMENT SYSTEM. A CONCEPTUAL SYSTEMS MODEL WHICH IS ALSO PRESENTED IS THE BASIS FOR SUBSEQUENT WORK AND WILL BE HELPFUL IN DEVELOPING A TRUE WORKING SYSTEMS MODEL. AN ATTEMPT IS MADE TO RELATE THE INPUT VARIABLES WITH CURRENT STATE-OF-ART INSTRUMENTATION IN ORDER TO MEASURE PAVEMENT RESPONSE. /AUTHOR/

Discussion of “Airfield Pavement Design of the Corps of Engineers”

Discussion of “Airfield Pavement Design of the Corps of Engineers”

Design and Construction of Heavy-Duty Airfield Pavements at Edwards Air Force Base

Design and Construction of Heavy-Duty Airfield Pavements at Edwards Air Force Base

The Design and Construction of Airfield Pavements

Before the Second World War there were few airfields in Great Britain with paved runways.The grassed flight strips of the pre-war years could carry the wheel loads of the aircraft then in use with little maintenance, other than grass cutting and rolling clinker or stone into local soft patches. From 1939 onwards, the increasing weight of aircraft, and more intensive flying, made it necessary to construct airfields with paved runways to permit operation in all weathers.From 1939 to 1945, 444 airfields were constructed with paved runways for the Royal Air Force at a cost of £200,000,000, excluding the cost of building construction. Since 1945 the emphasis has been upon airfields for civil use, and the great airfields at Idlewild, Boston, Johannesburg and London Airport have been built.

Adaptation to the Design of Airfield Pavements

In the development of the design method based on the use of the CBR, test, the California Division of Highways tested adequate sections of flexible highway pavements and sections that failed and correlated the service behavior of the pavement with its bearing ratio. These data were consolidated into a design chart as explained in paper No. 2. This design chart shows the total thickness of base and surfacing required for a flexible highway pavement on a subgrade with a given CBR value. On this chart (see Fig. 5), as stated by Mr. Porter, curve A represents a total thickness of pavement and base course above the subgrade adequate for average highway traffic conditions, and curve B indicates the total thickness considered to be the minimum requirement for light highway traffic.