National Airport Pavement Test Facility Research Articles

Evaluation of Airport Pavement Base Layer Stiffness Characteristics via Embedded Field Sensors

Real-time stiffness monitoring of unbound aggregate layers using embedded field sensors is crucial for advanced airport pavement design and management. This paper describes research findings on monitoring base layer stiffness characteristics for airport pavements using an embedded bender element (BE) field sensor, inductive coil sensors, and pressure cells. A full-scale pavement test section was constructed at the Federal Aviation Administration (FAA)’s National Airport Pavement Test Facility (NAPTF). A BE field sensor, inductive coil sensor pairs, and pressure cells were installed in the unbound aggregate base to evaluate the layer stiffness, applied load stress, and deformation characteristics. A triple dual tandem gear loading module applied 58,000 lb per wheel to the tested section with a wander pattern consisting of 66 passes arranged in nine lateral wander positions. Dynamic responses of coil sensors and pressure cells were collected during the traffic test, whereas BE signals were collected after completing each wander pattern. Laboratory repeated load triaxial tests with BE instrumentation were also conducted to establish a correlation for converting BE field sensor readings to layer modulus properties. The in situ modulus characteristics of the aggregate base layer were evaluated during full-scale testing using two methods: shear wave velocities from a BE field sensor, and strain and stress measurements from coil sensors and pressure cells. The moduli estimated using both approaches fell into typical ranges of crushed aggregate bases and were highly comparable. The moduli from the dynamic sensor measurements clearly showed the effect of vehicle wander on aggregate base layer measured responses.

Shear failure investigation of unbound pavement layers under accelerated heavy aircraft loading: case study

ABSTRACT Airport pavements are designed to sustain aircraft-induced stresses while maintaining adequate serviceability. To enhance pavement design procedures, the Federal Aviation Administration (FAA) utilises the National Airport Pavement Test Facility (NAPTF) to perform full-scale tests of airfield pavements under representative tire loads. Due to higher tire loads and pressures, unbound layers may experience shear failure and excessive permanent deformation. In this study, a new methodology is proposed to estimate the shear strength parameters of unbound materials by extrapolating resilient modulus test data until failure by adopting the hyperbolic stress–strain constitutive soil model. Using those shear strength parameters of unbound pavement layers of the NAPTF Construction Cycle 3 (CC3), a comprehensive simulation was performed using a modified version of SuperPACK (Super Heavy Load Pavement Analysis PACKage), developed based on the Federal Highway Administration (FHWA) Analysis Methodology for superheavy load (SHL). Pavement behaviour and performance were investigated for four FAA flexible pavement configurations tested mainly to study the role of different subbase thicknesses. It was found that modified SuperPACK was able to reasonably predict the shear failure mechanism in the different unbound layers existing in CC3.

Airport Pavement Stiffness Monitoring and Assessment of Mechanical Stabilization using Bender Element Field Sensor

The bender element (BE) field sensor is a newly developed embedded pavement instrumentation that measures shear wave velocity to estimate constructed layer moduli of unbound aggregate bases and subbases. This paper presents findings related to monitoring stiffness characteristics of airport pavement base courses instrumented with BE field sensors and tested under full-scale accelerated pavement testing during Construction Cycle 9 (CC9) of the National Airport Pavement Test Facility (NAPTF) by the U.S. Federal Aviation Administration (FAA). The CC9 aggregate base courses were constructed following FAA’s P-209 specification for a geosynthetic experiment using a biaxial geogrid installed at the bottom of the 8-in. (203-mm) thick base in the north test section, while the control pavement in the south test section was built without a geogrid. Two BE field sensors were installed in the north and south test sections approximately 1 in. (25 mm) above the base–subbase interface. Multiple stages of aircraft gear loads, including static dual-gear, dynamic slow-roll (moving wheel), and dynamic proof-roll, were applied to the test sections. BE field sensor data collected throughout multiple loading stages were used to investigate the stiffness characteristics of the pavement base. These preliminary tests conducted at the NAPTF CC9 experiment revealed the effects of static and dynamic aircraft gear loads on the stiffness of the aggregate base layer and how confinement influenced the moduli of the geogrid-stabilized base. Further, previously observed anti-shakedown effects caused by vehicle load wander could be quantified through changing base course modulus and deformation behavior from the BE field sensor data analysis.

Evaluation of the response from the rigid pavement analysis system (RPAS) program for the characterisation of jointed concrete pavements

ABSTRACT The methodology behind the current mechanistic-empirical design of jointed concrete pavements (JCP) is not very sensitive to the properties of the foundation layers of a pavement system. For this reason, it is essential to develop an analysis tool that is capable of accurately capturing the influence of these supporting layers. To address the limitations of utilising simplified models for the prediction of concrete pavement responses, researchers at The University of Texas at El Paso have developed a finite element modelling tool (called Rigid Pavement Analysis System, RPAS) that incorporates a three-dimensional layered foundation. This paper presents the results of the verification of the 3-D foundation model in RPAS and the validation of this analysis tool with field and accelerated testing data. Response data from a standard truck load and a falling weight deflectometer from pavement sections at the MnROAD pavement testing facility were used to evaluate the performance of RPAS in modelling highway pavements. Response data from accelerated pavement testing on instrumented pavement sections at the National Airport Pavement Test Facility (NAPTF) were also used to evaluate the capabilities of RPAS in modelling heavy aircraft traffic. The results obtained from RPAS determined that the field responses were a good measure to validate the reliability of the analysis tool.

Time-dependent Drucker-Prager-Cap model coupled with PANDA (Pavement Analysis Using Nonlinear Damage Approach) to predict rutting performance of flexible pavements

An extended Drucker-Prager-Cap-Creep (D-P-Cap-Creep) constitutive relationship is coupled with the PANDA (Pavement Analysis using Nonlinear Damage Approach) model to predict rutting in granular and asphalt layers of flexible airfield pavements, respectively. The presented model treats the pavement structure as a system and predicts rutting performance as the summation of permanent deformation in the subgrade, subbase, base, and asphalt layers. In addition to capturing the effects of densification and shear on permanent deformation with the D-P-Cap model, a creep law is defined to capture time- and rate-dependent behavior of granular layers and the subgrade. Simulation results of D-P-Cap-Creep constitutive relationship in conjunction with PANDA are validated against test sections of Construction Cycle 3 (CC-3) at the National Airport Pavement Test Facility (NAPTF). Presented results demonstrate that incorporation of time hardening Creep law to D-P-Cap model resulted in reduction in deviation between field measurements and model predictions. It is argued that the D-P-Cap-Creep constitutive relationship may have a more pronounce effect on rutting evolution of flexible pavements with moist subgrades with high clay contents.

Accelerated Pavement Testing of Perpetual Pavement Test Sections under Heavy Aircraft Loading at FAA’s National Airport Pavement Test Facility

Abstract Six flexible pavements were constructed for construction cycle 7 (CC7) at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility in Atlantic City, New Jersey. Four test sections on the north side measure 200 mm (LFP-4), 250 mm (LFP-3), 300 mm (LFP-2), and 375 mm (LFP-1) that are made of hot mix asphalt (HMA) over an aggregate subbase (thickness varying between 850 and 1,025 mm) resting on a subgrade with a California bearing ratio of 5.5. The fifth test section, LFC-5, is conventional flexible pavement with 125 mm of HMA over aggregate base and subbase, and the LFC-6 structure is the same as LFC-5 except that the crushed stone base layer is replaced with asphalt-stabilized drainable base. The objective of CC7 tests is to develop perpetual pavement design criterion and to validate or refine the fatigue model for HMA in airport pavement thickness design software FAARFIELD. The HMA fatigue model is based on the ratio of dissipated energy change (RDEC). Four fiber optic strain plates were installed to measure transverse and vertical strains at top and transverse strains at bottom within the HMA layer. Full-scale accelerated pavement tests were performed. Traffic test load parameters were six-wheel gear, 245-kN wheel load (gear load 1,470 kN), and 4-kmph speed. Pavement performance was monitored using crack maps, straight edge rut depth, and surface profile measurements. LFC-5 and LFP-4 showed significant fatigue cracks and rutting. LFP-1 and LFP-2 performed well with no signs of cracking. This article presents a discussion on the RDEC fatigue model, pavement thickness design, pavement material characterization test results, pavement instrumentation, accelerated pavement tests under heavy aircraft gear loads, and pavement responses measured using embedded sensors. The test section performance shows that, under loading conditions used in the study, by increasing HMA thickness from 25.4 to 30.5 cm, fatigue cracking was eliminated for the duration of testing (38,000 passes).

Instrumented flexible pavement responses under aircraft loading

ABSTRACT The FAA National Airport Pavement Test Facility (NAPTF) is a full-scale accelerated pavement testing facility located in Atlantic City International Airport, New Jersey. Six flexible and three rigid test sections were built, instrumented and trafficked by Boeing 777 and 747 gears as part of construction cycle one. One flexible test section with an asphalt-stabilised base over a low-strength subgrade was considered in this study. All dynamic sensors, including pressure cells, strain gauges and multi-depth deflectometers were evaluated. A multistep procedure for evaluating the dynamic sensors was developed, and it included data reliability, repeatability, changes in the pavement responses under the Boeing 777 and 747 gears, and comparison with a three-dimensional (3D) finite element (FE) mechanistic model. The mechanistic model was found to predict the pavement responses with good reliability, whenever representative layer moduli are used. The study also found that 60% of the sensors produced acceptable or marginal responses and 40% produced unacceptable responses; therefore, it is recommended to consider this sensor survival rate when instrumenting future test sections. The rutting performance and pavement responses over time were evaluated; the test section was shown to have relatively similar performance and pavement responses under the Boeing 777 and 747 gears.

Validation of the subgrade shear strength parameters estimation methodology using light weight deflectometer: Numerical simulation and measured testing data

Abstract Shear strength parameters (angle of internal friction, ϕ, and cohesion, c) of a soil medium are the key properties for the bearing capacity and stability analyses. The strength parameters have been recognized as one of the most reliable mechanical properties of pavement subgrade that can be used to estimate its permanent deformation behavior under repeated loading. In addition, when a pavement structure is subjected to a non-standard superheavy vehicle load (i.e., gross vehicle weight in excess of a few million pounds), investigation of instantaneous shear failure or onset of yielding in the pavement subgrade layer requires the knowledge of the strength parameters. Light Weight Deflectometer (LWD) has been commonly used as a Non-Destructive Test (NDT) method for in-situ determination of stiffness properties of pavement layers, unpaved roads, and subgrade layer during the construction process. In this study, the validity of a recently developed LWD-based methodology for estimating the in-situ shear strength parameters of the pavement subgrade layer has been further investigated. In this methodology, the commonly accepted hyperbolic stress-strain constitutive soil model along with the consideration of stress dependency of subgrade materials under multiple LWD load levels have been incorporated. The methodology was validated using numerically simulated LWD testing at multiple load levels for two different subgrade materials. In addition, the LWD data collected from large-scale experiments conducted at University of Nevada, Reno testing facility and National Airport Pavement Test Facility were also utilized to verify the methodology. It was found that the proposed LWD-based methodology provides a reasonable estimate for the in-situ shear strength parameters of the compacted soil subgrade.

Iterative Framework for Performance and Environmental Impacts of Airfields

The main goal of a durable and sustainable airfield is to withstand repeated aircraft traffic loading while minimizing the environmental impact. The objective of this study is to develop a design-life cycle assessment (LCA) framework considering a balanced evaluation of structural adequacy, minimizing emission, and optimizing total energy demand. To achieve this objective, three steps are introduced: an evaluation of the structural adequacy of the design using the Federal Aviation Administration (FAA) pavement design software FAA rigid and flexible iterative elastic layered design; a preliminary performance check using field instrumentation responses; and a LCA of airfield sections using both deterministic and probabilistic approaches. In addition to presenting the design-LCA methodology, this paper offers a comparative evaluation that covers two perpetual designs (LFP1-N and LFP4-N) and one conventional section (LFC5-N). These pavement sections were built and tested at the National Airport Pavement Test Facility as part of construction cycle 7, funded by the FAA. Responses collected from instrumentation were used to compute field-based coverages to failure. Moreover, life cycle inventories from secondary sources were used to quantify the greenhouse gas emissions and energy demand associated with the construction of these sections. Results show inconsistencies between the field-predicted and theoretically predicted performance. This suggests the need for the additional calibration of the currently used performance models. Moreover, this study shows that under a specific asphalt concrete (AC) thickness limit, conventional AC may be more eco-friendly than a perpetual design.

Laboratory characterization of temperature induced reflection cracks

Abstract A hot-mix asphalt (HMA) overlay is one of the primary strategy for rehabilitating existing HMA pavements and Portland cement concrete (PCC) pavements. The current design program, FAARFIELD, does not address reflective cracking for asphalt-overlaid concrete pavements due to its mechanism complexity. The bending, shearing, and thermal are three crucial factors to successfully model reflective cracking. To implement this failure mode in flexible over rigid design procedure, a series of full-scale test pavements were constructed, instrumented, and tested in the condition of extreme cooling temperature at the FAA National Airport Pavement Test Facility. The purpose was to assess cooling effects on the propagation of reflection cracks for airport AC over PCC pavements. In preparation for reflective cracking phase VI test, the FAA is conducting laboratory experiment on field extracted hot mix asphalt (HMA) cores. In order to test these field HMA cores, the Texas Overlay Tester (OT) was customized to get data similar to the full-scale tests. This paper discusses finite element analysis on the full-scale testing, development of the customized Texas OT, and a laboratory testing suite using the customized Texas OT, including preliminary tests, instrumentation, experiment design, and test results. Data obtained from this research effort will be used to develop a rational testing procedure to simulate extreme cooling cycles through full-scale testing.

Airfield Pavement Damage Evaluation Due to New-Generation Aircraft Wheel Loading and Wander Patterns

This paper presents a stress-history-based approach to predict the deformation basins of airport pavements subjected to heavy aircraft loading applied in sequential wanders. Multi-depth deflectometer data from full-scale aircraft landing gear tests conducted at the National Airport Pavement Test Facility built by the Federal Aviation Administration are used to create individual pass residual deformation transverse profiles. The computed residual deformation profiles are further corrected for stress-history effects to predict rut in the selected test sections. The developed model focuses on using the previous load location and stress history of the soil element to develop the deformations in that element. Despite the unavailability of the surface transverse profile data measured in the field at different passes, the initial attempt of the model can closely predict the deformation profile similar to width and shape expected in the field. And after the stress-history effects are accounted for, the initially calculated rut depth decreases significantly to match the final contour basin of the test sections extracted from the post traffic trenching. The advantage of using the stress-history-effects-based rut prediction tool is that it can allow any combination of wander positions and sequences of load applications to be accounted for their effects on the final surface rut development.

Multi-wheel gear loading effect on load-induced failure potential of airfield flexible pavement

ABSTRACTThis study aimed to investigate the effect of multi-wheel loading gear configuration on loading-induced failure potential of airfield flexible pavements. Field response testing was conducted in the National Airport Pavement Test Facility (NAPTF) using different multi-wheel gear configurations. Three-dimensional (3-D) finite element (FE) models were developed to simulate multi-wheel loading along with non-uniform tyre contact stresses. The 3-D FE models were validated by tensile strains measured from response testing. The effects of wheel loading configurations and magnitudes on different strains responses were compared for two pavement sections with different asphalt layer thicknesses. Analysis results showed that six-wheel gear configuration caused the greater pavement responses. The critical shear strains were found greater than critical tensile strains at the same loading condition and pavement structure, especially for thick asphalt pavements. This is consistent with top-down cracks observed at field sections after traffic testing. On the other hand, shear strains increase more rapidly as the load level increases as compared to tensile strains; while thin asphalt layer is more sensitive to loading magnitude as compared to thick asphalt layer. The multi-wheel effect on fatigue life is more significant for thick pavement due to the load superposition effect under different wheels.

Evaluation of Asphalt Drainable Base Structural Performance for Flexible Airport Pavement Design

In 2014, the Federal Aviation Administration’s (FAA) National Airport Pavement Test Facility (NAPTF) completed construction of its flexible pavement test section, Construction Cycle 7 (CC7). Among the objectives of CC7 was to study the performance of an asphaltic drainable base pavement section compared with a P-209 aggregate base pavement section under full-scale airport loading. This research addresses the pre-traffic material characterization, full-scale traffic test data analysis and post-traffic test data analysis of these two pavement sections in dry conditions. This paper will discuss the preliminary results from laboratory testing and full-scale traffic tests for material properties which may be used in design and construction specifications to improve FAA pavement design software (FAARFIELD).

Effect of Pavement Structure on the Mechanical Response and Performance of Perpetual Pavements at the National Airport Pavement Test Facility

Construction Cycle 7 (CC7) conducted at the FAA National Airport Pavement Test Facility (NAPTF) was aimed to study the effect of hot mix asphalt (HMA) layer thickness and develop perpetual pavement design criterion for airfield flexible pavements. Four fully instrumented perpetual test pavements were designed, constructed, and tested, with all test items trafficked under heavy aircraft loads using a three duals in tandem configuration. Pavement condition was monitored using heavy weight deflectometer tests, distress surveys, and surface profiles. Comprehensive response data analysis revealed that increasing HMA layer thickness significantly reduced the tensile strain at the bottom of the HMA layer, permanent deformation in the unbound layer, and vertical stress at top of the subgrade. Thicker HMA test items exhibited better rutting performance, as evidenced in both multiple depth deflectometer and surface profile data. The interaction between HMA layer temperature and thickness was captured in the pressure cell responses. More tests are planned to determine the threshold HMA strain to prevent fatigue cracking.

Development of Domain Analysis to Predict Multi-Axial Flexible Airfield Pavement Responses Due to Gear and Environmental Loadings

Flexible pavement design procedures use maximum mechanistic strains to predict service life via empirical transfer functions. The conventional method of using predefined point locations for potential damage may not accurately represent realistic pavement scenarios. For instance, flexible airfield pavement analysis mainly considers the critical strain at the bottom of the asphalt concrete (AC), which may not characterize near-surface cracking potential. In lieu of point strains, domain analysis, a new method, accounts for the multi-axial behavior of pavements, as inherently excited by three-dimensional (3-D) and nonuniform aircraft tire–pavement contact stresses. Initially applied on highway pavements considering truck tire loading, this approach is an initial breakthrough for implementing domain analysis on flexible airfield pavements; in this study, A-380 and F-16 landing gear tire loads were considered. As anticipated, speed and temperature had significant influence on cumulative domain stress and strain ratios. The decrease in speed and increase in temperature not only increased the cumulative ratios up to 1.81, but nonlinearity of the problem became more prevalent at worst loading conditions (8 kph and 45°C). Minimal difference in ratios for F-16 cases suggests that the National Airport Pavement Test Facility pavement structure became less sensitive to conditions under low loads. Point response analysis revealed that critical strains were not significantly influenced by the tire-inflation pressure, for example, tensile strain at the bottom of the AC only increased up to 13.6% (considering 8 kph speed), whereas domain analysis quantified the increase with respect to 3-D stress or strain states.

Correlating laboratory and full-scale reflective cracking tests for airfield pavements

Asphalt overlays minimize moisture infiltration and help in restoring the smoothness and structure of existing airfield concrete pavements, but due to reflective cracking, the new asphalt overlay often fails before achieving its design life. In airfields, the potential for reflective cracking presents a major challenge for rigid pavement rehabilitation involving asphalt overlays. To assist airport engineers and others concerned with the temperature-induced reflection cracks, several full-scale test pavements have been constructed, instrumented, and tested at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The main objective of this study was to identify and develop correlations between full-scale and laboratory reflective cracking tests. A customized Overlay Tester (COT) and Cyclic Disc-Shaped Compact Tension (CDCT) Test were used evaluate the fracture and fatigue performance of hot mix asphalt (HMA) materials at low temperatures. The COT was conducted at the same conditions as the full-scale tests and test results were analyzed using several parameters. Temperature effect was pronounced in strain parameters (initial strain, failure strain, and strain at Nf(NLC)). Further fatigue parameters (Nf(crack) and Nf(NLC)) indicated a swifter deterioration of HMA mixture at a higher displacement (cooling) rate. Fracture parameter (Gfini) was found to decrease with the increase of displacement rate due to the brittleness of HMA at low temperatures as excepted. A two-term exponential function from the CDCT tests demonstrated the fracture behavior of HMA under cyclic loading. The released energy rate factor (R2) correlated well with the fatigue life. Finally, a set of shift factors were derived between the full-scale, OT, and CDCT tests. Valuable data obtained from this study provides immediate support to the future FAA reflective cracking research.

Rutting prediction in airport pavement granular base/subbase: A stress history based approach

Abstract Test data from full-scale aircraft gear loading conducted at the National Airport Pavement Test Facility (NAPTF) by the US Federal Aviation Administration (FAA) were analyzed to investigate the effects of wander (offset loads) and channelized traffic loadings on the deformation behavior of unbound aggregate layers in asphalt pavement test sections. Insights were drawn on the complex rebound (recovered) and residual (unrecovered) deformation trends of granular materials due to passing of each of the 6-wheel Boeing 777 (B777) and the 4-wheel Boeing 747 (B747) gears for various combinations of loading (stress history effects), wander positions, and wander sequences. Measured field layer deformations and the accumulation rates could only be achieved when the magnitudes and variations of stress states in the granular layers, number of load applications, gear load wander patterns, previous loading stress history effects, trafficking speed or loading rate effects, and finally, principal stress rotation effects due to moving wheel loads were properly accounted for. Accordingly, measured transverse profiles and multi-depth deflectometer data were used to create individual pass residual deformation transverse profiles. The created transverse profiles were then combined with stress history effects to predict the residual transverse profiles for the test sections with P209/P154 granular base/subbase layers. The proposed method emphasizes the use of the previous load location and stress history of the pavement element to develop the residual deformation in that element. Calculation of the residual deformation in each element across the pavement surface results in the development of the complete permanent deformation transverse profile. This technique can be applied to estimate the transverse rutting profile of the pavement after trafficking based on any combination of applied wander and traffic direction.

Estimating fatigue endurance limits of flexible airfield pavements

In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based FEL for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling weight deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (Nf50). NAPTF tensile strain data were also used to determine the tensile strain at Nf50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the rate of dissipated energy change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted vs. number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gauge data increased was used as an estimate of a possible FEL. The Nf50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.

Impact of dynamic loading on backcalculated stiffness of rigid airfield pavements

The objective of this paper was to evaluate the deterioration of Portland Cement Concrete (PCC) slabs throughout trafficking. A full-scale accelerated pavement testing at the National Airport Pavement Test Facility (NAPTF) was conducted on Construction Cycle 6 (CC6) on rigid pavements with low, medium and high flexural strengths on both a concrete and asphalt stabilised base. Heavy Weight Deflectometer (HWD) testing was conducted on the test sections to backcalculate the stiffness of the layers. The majority of PCC deterioration occurred roughly within the first 1500–2000 passes of trafficking. On average, the MRS-1 (low flexural strength) PCC elastic modulus was found to decrease by 20%, from 5.0–.4 × 106 (34.5–37.2 GPa) to 4.0–4.3 × 106 psi (27.6–29.7 GPa), whereas the PCC elastic modulus of MRS-2 and MRS-3 was found to decrease by 17% and 22%, respectively. However, neither the MRS-2 nor MRS-3 elastic modulus was found to drop below 5.0 × 106 psi (34.5 GPa) after 15,000 passes.

Airfield Pavement Response Caused by Heavy Aircraft Takeoff

The effect of wheel configuration on critical airfield pavement responses during takeoff was calculated, and variables, usually omitted in conventional pavement analysis, were considered. The numerical analysis matrix consisted of two takeoff speeds, two inflation pressures, two pavement structures, and four wheel configurations. One of the pavement structures was built at the National Airport Pavement Test Facility and had been previously described in the literature. The method used in this study advanced current knowledge in two respects. First, the study examined not only the tensile strains at the bottom of the asphalt concrete (AC) layer (fatigue cracking) and vertical strain on top of the subgrade (rutting) but also the transverse surface strain (surface cracking) and vertical shear strains (near-surface cracking and rutting). Second, several assumptions about existing methods were advanced. These assumptions included (a) nonuniform three-dimensional contact stresses instead of uniform one-dimensional vertical stresses over a circular contact area, (b) viscoelastic and nonlinear material characterization for AC and granular material under high stress levels in lieu of a linear elastic model, and (c) load variation with time to reflect takeoff. Transverse surface strain and vertical shear strain in the subgrade were most affected by wheel configuration. In addition, the variables had varying influence on pavement responses and wheel interaction. For instance, takeoff speed affected vertical strain on top of the subgrade but did not affect transverse surface strain. Tire inflation pressure modified wheel interaction for shear strain in the AC but not in the subgrade.