PURPOSES : The objective of this study is to develop regression models for surface distress (SD), rut depth (RD), and international roughness index (IRI) of Jeju Island local road by analyzing the correlations between the pavement performance and its influencing factors. METHODS : First, the differences between pavements in inland Korea and Jeju Island in terms of performance and influencing factors were investigated. Influencing factors were assigned to pavement sections on Jeju Island using the inverse distance weighting method, and the correlations between the pavement performance and influencing factors were analyzed. As a result, maximum temperature, heat wave days, annual temperature range, precipitation days, precipitation intensity, ESAL, etc. were determined as independent variables for the pavement performance prediction models. Multiple regression analysis was performed to develop the pavement performance models using the selected independent variables. RESULTS : The RD, maximum temperature, and precipitation days were determined to be the independent variables for the SD predictive model. The SD, maximum temperature, annual temperature range, heat wave days, and precipitation days were selected as independent variables of the RD prediction model. In addition, the RD, annual temperature range, heat wave days, precipitation days, and ESAL were selected as independent variables for the IRI prediction model. CONCLUSIONS : As a result of the study, an actual forecast model for SD, RD, and IRI was developed. Based on this model, it is possible to estimate the predictive value of the missing performance data in the studied interval. If the factors affecting performance are managed in terms of maintenance beyond a certain level, it can help those responsible for road maintenance to rationally select the maintenance method and timing.

PURPOSES : The surface distress of asphalt pavements is one of the major factors affecting the safety of road users. The aim of this study was to analyze the factors influencing the occurrence of surface distress and statistically predict its annual change to contribute to more reasonable asphalt pavement management using the data periodically collected by the national highway pavement data management system. METHODS : In this study, the factors that were expected to influence the surface distress were determined by reviewing the literature. The normality was secured by changing the forms of the variables to make the distribution of the variables got closer to normal distribution. In addition, min-max normalization was performed to minimize the effect of the unit and magnitude of the candidate independent variables on the dependent variable. The final candidate independent variables were determined by analyzing the correlation between the annual surface distress change and each candidate independent variable. In addition, a prediction model was developed by performing data grouping and multi-regression analysis. RESULTS : An annual surface distress change prediction model was developed using present surface distress, age, and below 0 ℃ days as the independent variables. As a result of sensitivity analysis, the surface distress affected the annual surface distress change the most. The positive correlation between the dependent variable and each independent variable demonstrated engineering and statistical meaningfulness of the prediction model. CONCLUSIONS : The surface distress in the future can be predicted by applying the annual surface distress prediction model to the national highway asphalt pavement sections with survey data. In addition, the prediction model can be applied to the national highway pavement condition index (NHPCI) evaluating the national highway asphalt pavement conditions to be used in the prediction of future NHPCI.

PURPOSES : On a thin epoxy overlay pavement, epoxy is placed on the existing bridge deck pavement, followed by the spraying of aggregates on it. The bond strength between the existing pavement and overlay pavement is an important factor representing the performance of the thin epoxy overlay pavement, in addition to the skid resistance and roughness. Therefore, the bond strength, skid resistance, and roughness of a thin epoxy overlay pavement constructed for field tests under various field conditions are examined in this study. METHODS : The usability of epoxy and aggregates on a thin epoxy overlay pavement is identified by testing their material properties in a laboratory. A construction test is performed using the pretreatment conditions of the existing pavement surface and the number of layers of overlay pavement as variables. The bond strength, skid resistance, and roughness are analyzed 3 d after constructing the test pavement, and immediately before and after applying repetitive traffic loadings at 6 months. RESULTS : When the existing pavement is in good condition, as in this study, the bond strength of the thin epoxy overlay pavement is affected more significantly by the existing pavement condition than the material properties of epoxy, in which destruction is indicated in the existing pavement. The skid resistance is affected primarily by the condition of the aggregates sprayed on the epoxy. The pavement on which the aggregates are well sprayed indicate a high skid resistance. The roughness is not affected by any variables, such as the pretreatment conditions, number of thin pavement layers, and repetitive traffic loadings. CONCLUSIONS : A long-term evaluation of the bond strength, skid resistance, and roughness will be conducted on a test pavement. In addition, another construction test will be performed to investigate the performance of a thin epoxy pavement overlaid on a bridge deck pavement under inferior conditions.

PURPOSES : For high driving performance and service life of cement concrete pavement, construction quality must be secured. The construction quality is to be measured after pavement construction, but in this case, it is difficult to improve construction quality. Therefore, it is necessary to develop a method for measuring and correcting the profile of the pavement and subbase so that the construction quality can be monitored immediately after construction. METHODS : The device that can measure the construction quality of cement concrete pavement has been developed. Through the experiment simulating the field situation, the profile of the pavement and subbase was measured and calibration method was developed. RESULTS : In the measured profile, an outlier by the sensor and noise by the sensor and vibration were measured, and a step-like profile was measured differently from the acture one. To remove outliers, the boxplot outlier removal method was applied by overlapping each data group. The noise were removed by a low pass filtering. And, it was calibrated to a profile similar to the acture one through the sampling interval adjustment and the weighted moving average method. CONCLUSIONS : The method that can measure and calibrate the profile that is almost identical to the actual one has been developed. Accordingly, it is expected that the performance of the pavement can be improved by accurately monitoring the construction quality immediately after construction.

PURPOSES : Rut depth of asphalt pavements is a major factor that affects the maintenance of pavements as well as the safety of drivers. The purpose of this study was to analyze the factors influencing rut depth, using data collected periodically on national highways by the pavement management system and, consequently, predict annual rut depth change, to contribute to improved asphalt pavement management. METHODS : The factors expected to influence rut depth were determined by reviewing relevant literature, and collecting the related data. Further, the correlations between the annual rut depth change and the influencing factors were analyzed. Subsequently, the annual rut depth change model was developed by performing regression analysis using age, present rut depth, and annual average maximum temperature as independent variables. RESULTS : From the sensitivity analysis of the developed model, it was found that age affected the annual rut depth change the most. Additionally, the relationship between the dependent and independent variables was statistically significant. The model developed in this study could reasonably predict the change in the rut depth of the national highway asphalt pavements. CONCLUSIONS : In summary, it was verified that the model developed in this study could be used to predict the change in the National Highway Pavement Condition Index (NHPCI), which represents comprehensive conditions of national highway pavements. Development of other models that predict changes in surface distress as well as international roughness index is required to predict the change in NHPCI, as they are the independent variables of the NHPCI prediction model.

PURPOSES : Given that large-scale repair works of expressway bridge pavements have high maintenance cost and long traffic blocking time, the thin overlay method that maintains the existing pavement is attracting attention. In this study, because the bridge thin overlay has not been introduced in Korea yet, the basic physical properties of the epoxy thin overlay, which is mainly used for the bridge thin overlay, were investigated, and the skid resistance and bond performance were analyzed. METHODS : Basic physical property tests were performed on each of the epoxy binders, aggregates, and mixtures used in epoxy thin overlay. They were also compared and reviewed against foreign standards. The epoxy binders were tested for viscosity, gel time, and thermal compatibility. The aggregates were tested in terms of water absorption, specific gravity, and gradation. The compressive and flexural strengths of the mixtures were investigated. The epoxy thin overlay has the possibility of detachment of aggregates, so the skid resistance was tested according to the paving phase. In addition, to investigate the bond performance, which is the most important performance of the epoxy thin overlay, the bond strength test was performed by varying the moisture condition and treatment condition of the existing layer surface. RESULTS : The basic physical properties of the materials used in the epoxy thin overlays satisfied foreign standards except for the gradation of aggregates. The skid resistance did not satisfy the standard when the epoxy was exposed, whereas the skid resistance did satisfy the standard when the aggregates were exposed, even after the abrasion test. The bond strength of the epoxy thin overlay satisfied the standard in all cases. The bond strength was the highest when the relative humidity of the existing layer surface was 60%. CONCLUSIONS : The materials of epoxy thin overlay that could be obtained in Korea satisfied the basic physical property standards except for aggregate gradation. Given that the aggregate gradation could be adjusted, it can be concluded that the epoxy thin overlay could be introduced in Korea. In addition, it was confirmed that the skid resistance and bond strength of the epoxy thin overlay were high enough to be used in general road conditions. It was determined that the existing layer surface should maintain an optimal relative humidity of approximately 60% because the moisture condition affects the bond strength.

PURPOSES : The purpose of this study was to investigate the performance of additives that affect internal curing in order to reduce the damage occurring in concrete pavements. METHODS : SAP was used as an additive to reduce internal curing in concrete pavements. SAP is an additive that has a very high absorption rate which prevents concrete wrappers from externally draining water. To evaluate the internal curing performance according to the ratio of SAP, we identified the number of cracks and amount of abrasion reduction. RESULTS : Plastic shrinkage and durability of a concrete mixture with added SAP were evaluated. The following results were obtained: (1) SAP showed a tendency to reduce slumps due to absorption of the concrete mixture. (2) It was possible to verify that concrete condensation did not occur during the penetration resistance test and that the initial curing did not lead to reactions within the mixture. (3) Adding more than 0.6% of SAP for dry curing resulted in greater compressive strength at all ages than OPC, with the highest compression strength of 0.9% after 56 days. (4) Regarding abrasion resistance, it was found that adding SAP was 30~50% better than adding the OPC mixture, and at 0.9% compression strength, abrasion resistance showed the best performance. (5) In the chlorine ion immersion resistance experiment, the passing charge of the OPC mixture was rated “high,” but it was rated “normal” in SAP. The results showed that the addition of SAP improved the water density of concrete due to internal curing effects, and that it showed the greatest chlorine ion penetration resistance for a compressive strength of 0.9%. (6) Regarding plastic shrinkage resistance, cracks did not occur on the surface until the end of the experiment, but the plastic shrinkage rate upon addition of SAP was relatively low compared to that of the OPC mixture. CONCLUSIONS : Recent studies have shown that internal curing techniques can be applied using SAP to prevent shrinkage due to the loss of water and to decrease the effects of hydration. If internal curing effects are expressed using SAP, it is thought that contraction due to a loss of moisture and reduction in sign language reaction can be prevented.

PURPOSES : The type and degree of structural conditions and influencing factors distributed across representative sections should be similar to those distributed across entire sections as the representative sections have been predominantly used for developing performance prediction models, which substitute entire sections of road pavement. Therefore, a logic that selects the representative sections with similar distributions of structural conditions and the influencing factors with those of entire expressway asphalt pavement sections requires development. METHODS : The logic developed in this study to select the representative sections of asphalt pavements comprised three steps. First, the data on the structural conditions of the pavement and the influencing climate conditions and pavement materials were collected and organized. Consequently, in the second step, the candidate sections were selected, with the severity of the structural conditions of the pavement distributed widely and evenly. Finally, in addition to the widely and evenly distributed pavement conditions, the representative sections with climatic conditions and pavement materials were selected. RESULTS : A total of 6,352 ordinary asphalt pavement sections and 596 composite asphalt pavement sections were selected as entire expressway asphalt pavement sections and the data were collected and organized according to the logic developed in this study. Three times the representation sections were selected as candidate sections and, finally, 85 sections were selected as representative sections. The distribution of structural conditions and influencing climate conditions and pavement materials in the representative sections were similar to those in the entire sections. In addition, the representative sections were spread evenly across the country. CONCLUSIONS : The sections presenting similar distributions of structural conditions and the influencing factors of entire expressway asphalt pavement sections could be selected in this study. Using the representative sections selected in this study, a remodeling index model will be developed for predicting the asphalt pavement sections that require large-scale repair.

PURPOSES : For large-scale construction, such as a concrete pavement, design and construction are not entirely consistent. If the inconsistency between design and construction is very large, construction quality is significantly degraded, affecting performance life span and driving comfort. The quality of pavement construction is managed according to standards. However, it is difficult to improve construction quality as the standard measures construction quality after construction is completed. Therefore, this study developed a system to measure the construction quality of concrete pavement in real-time and presented the corresponding standards. METHODS : A basic module for simultaneously measuring the width, thickness, and roughness of the concrete pavement was designed. Based on the measurement results of the distance measurement sensor, a calibration method is presented that can remove noise. The system process was developed to measure construction quality based on location and distance data, measured in real-time using GPSs and sensors. The field application experiment was conducted and the results were analyzed. RESULTS : The measurement module is properly designed to be used in concrete pavement construction sites. Noise was removed from the distance measurement sensor results according to the presented calibration method, leaving only the wave of pavement surface irregularities. As a result of applying the system process in the field application, a reasonable level of PRI was observed. CONCLUSIONS : In the past, the width, thickness, and roughness were measured after construction was completed and, if the standard was not met, construction quality control was performed via reconstruction or repair. Through this study, it is expected that the width, thickness, and roughness of the concrete pavement can be measured in real-time and, if the standard is not met, construction quality can be immediately controlled during construction to maintain high quality.

PURPOSES: Knowing the scope of deterioration of the concrete slab around spalling is important in determining the size of the partial-depth repair. The change in the material properties of the concrete slab, according to the severity of spalling and distance from spalling, is analyzed herein by performing non-destructive and destructive tests at the field and in the laboratory. METHODS: The test slabs were determined by finding spallings with high or medium severity. The relative elastic modulus was measured near the spalling, far from spalling, and around the slab center using an impact echo equipment. The core specimens were obtained at the measurement positions. An absorption test was performed for the core specimens, while the impact echo and dynamic modulus tests were performed for the upper and lower parts of the core specimens under dry or saturated conditions. A compressive strength test was also performed for the upper and lower parts of the core specimens. RESULTS : The absorption coefficient, relative elastic modulus, relative dynamic modulus, and relative compressive strength worsened as the measurement position became closer to the spalling distress and top of the slab. The worse material properties were measured for the spalling with a higher severity. The moisture condition of the specimens scarcely affected the material properties. CONCLUSIONS : The impact echo test results obtained at the field showed a high correlation with the results of the absorption, impact echo, dynamic modulus, and compressive strength tests performed in the laboratory. Accordingly, a quicker and a more convenient nondestructive soundness evaluation of concrete pavements is expected to be realized using the field impact echo test method.

PURPOSES : Almost every design method for airport concrete pavements considers only traffic loading and not environmental loading. This study proposes a mechanistic design method for airport concrete pavements, that considers both environmental and traffic loading simultaneously. METHODS: First, the environmental loading of concrete pavements in Korean airports was quantified. FEAFAA, a finite element analysis program for airport pavements, was used to calculate the maximum tensile stress (MTS) of the slab, caused by both environmental and traffic loadings. The factors that influence the MTS were identified via sensitivity analysis, and an MTS prediction model was developed using the statistical analysis program SPSS. The ratio of MTS to the tensile strength of slab was calculated using the prediction model. The fatigue model under the AC 150/5320-6E and AC 150/5320-6F standards of the FAA was corrected to make it suitable for the predicted stress-strength ratio. RESULTS : The MTS prediction model and corrected fatigue model were used to redesign the slab thickness and joint spacing of airport concrete pavements originally designed using the AC 150/5320-6D standard, which empirically considers traffic loading only. As a result, different slab thicknesses and joint spacings were redesigned with consideration for environmental loading, specifically the weather conditions of airports. . CONCLUSIONS: The slab thickness and joint spacing can be mechanistically designed at the same time, whereas previously, only the slab thickness was designed, and the joint spacing was determined empirically.

PURPOSES : It is well known that low temperature cracking is one of the most serious distresses on asphalt pavement, especially for northern U.S. (including Alaska), Canada and the northern part of south Korea. The risk of thermal cracking can be numerically measured by estimating thermal stress of a given asphalt mixture. This thermal stress can be computed by low temperature creep testing. Currently, in-direct tensile (IDT) mixture creep test mentioned in AASHTO specification is used for measuring low temperature creep properties of a given asphalt mixture. However, IDT requires the use of expensive testing equipment for performing the sophisticated analysis process, however, very few laboratories utilize this equipment. In this paper, a new and simple performance test (SPT) method: bending beam rheometer (BBR) mixture creep testing equipment is introduced, and the estimated experimental results were compared with those of conventional IDT tests. METHODS: Three different asphalt mixtures containing reclaimed asphalt pavement (RAP) and roofing shingles were prepared in the Korea Expressway Corporation (KEC) research laboratory. Using the BBR and IDT, the low temperature creep stiffness data were measured and subsequently computed. Using a simple power-law function, the creep stiffness data were converted into relaxation modulus, and subsequently compared. Finally, thermal stress results were computed from relaxation modulus master curve using Gaussian quadrature approach with condierations of 24 Gauss number. RESULTS: In the case of the conventional asphalt mixture, similar trends were observed when the relaxation modulus and thermal stress results were compared. In the case of RAP and Shingle added mixtures, relatively different computation results were obtained. It can be estimated that different experimental surroundings and specimen sizes affected the results. CONCLUSIONS: It can be said that the BBR mixture creep test can be a more viable approach for measuring low temperature properties of asphalt mixture compared to expensive and complex IDT testing methods. However, more extensive research and analysis are required to further verify the feasibility of the BBR mixture creep test.

PURPOSES : The performance of pavements is decreased by reduced bearing capacity, deterioration, and distress due to complex loading conditions such as traffic and environmental loads. Therefore, the proper maintenance of pavements must be performed, and accurate evaluation of pavement conditions is essential. In order to improve the accuracy of the heavy weight deflectometer (HWD), which is a nondestructive evaluation method, the correlation between HWD test results and temperature factors were analyzed in this study. METHODS : The HWD test was conducted five times for one day on airport concrete pavement, and the ambient temperature, surface temperature, and slab internal temperature were collected. Since the slab internal temperature was nonlinear, it was replaced by the equivalent linear temperature difference (ELTD). The correlation between the HWD test results and each temperature factor was analyzed by the coefficient of correlation and coefficient of determination. RESULTSAND: The deflection of the slab center, mid edge, and corner, and impulse stiffness modulus (ISM) showed significantly high correlation with each temperature factor, especially the ELTD. However, the load transfer Efficiency (LTE) had very low correlation with the temperature factors. CONCLUSIONS : It is necessary to analyze the effect of aggregate interlocking on LTE according to the overall temperature changes in slabs by conducting seasonal HWD tests. It is also necessary to confirm the effect of seasonal temperature changes on deflection and ISM.

PURPOSES: The purpose of this study is to verity the applicability of a portable small-loop electromagnetic survey method to underground cavity detection. METHODS: In order to evaluate applicability of the method, a test bed comprised of four sections was constructed. The two sizes of the four cavities artificially formed at two depths were contained in the test bed. Each cavity was positioned at center of each 6 m long section. Four types of pavement materials such as unpaved ground, bricks, asphalt, and concrete were used at every section. The portable small-loop electromagnetic device measured electrical conductivity as an exploration signal that varied according to the electrical properties underground. The electrical conductivity was converted into two-dimensional electrical resistivity distribution sections using an inverse analysis program. RESULTS : The results showed that the electrical resistivity of the non-cavity area was lower than that of the cavity area. The electrical resistivity increased as the measurement device moved closer to the cavity position. It was also found that the electrical resistivity values were not significantly affected by pavement type. The small cavity with diameter of 35 cm could be detected up to 1.2 m depth. CONCLUSIONS: Therefore, it was verified that the portable small-loop electromagnetic survey method is applicable to the detection of cavities in sections where ground subsidence is expected. This method can be effectively used for small-scale roads such as sidewalks, parkways, and side streets where large exploration equipment cannot enter.

PURPOSES : Previously, airport concrete pavement was designed using only aircraft gear loading without consideration of environmental loading. In this study, a multiple-regression model was developed to predict maximum tensile stress of airport concrete pavement based on finite element analysis using both environmental and B777 aircraft gear loadings. METHODS: A finite element model of airport concrete pavement and B777 aircraft main gears were fabricated to perform finite element analysis. The geometric shape of the pavement, material properties of the layers, and the loading conditions were used as input parameters for the finite element model. The sensitivity of maximum tensile stress of a concrete slab according to the variation in each input parameter was investigated by setting the ranges of the input parameters and performing finite element analysis. Based on the sensitivity analysis results, influential factors affecting the maximum tensile stress were found to be used as independent variables of the multi regression model. The maximum tensile stresses predicted by both the multiple regression model and finite element model were compared to verify the validity of the model developed in this study. RESULTS: As a result of the finite element analysis, it was determined that the maximum tensile stress developed at the bottom of the slab edge where gear loading was applied in the case that environmental loading was small. In contrast, the maximum tensile stress developed at the top of the slab center situated between the main gears in the case that the environmental loading got larger. As a result of the sensitivity analysis and multiple regression analysis, a maximum tensile stress prediction model was developed. The independent variables used included the joint spacing, slab thickness, the equivalent linear temperature difference between the top and bottom of the slab, the maximum take-off weight of a B777 aircraft, and the composite modulus of the subgrade reaction. The model was validated by comparing the predicted maximum tensile stress to the result of the finite element analysis. CONCLUSIONS : The research shown in this paper can be utilized as a precedent study for airport concrete pavement design using environmental and aircraft gear loadings simultaneously.

PURPOSES : The purpose of this study is to analyze the magnitude of shoving of asphalt pavement by junction type between airport concrete and asphalt pavements, and to suggest a junction type to reduce shoving. METHODS : The actual pavement junction of a domestic airport, which is called airport “A”was modified by placing the bottom of the buried slab on the top surface of the subbase. A finite element model was developed that simulated three junction types: a standard section of junction proposed by the FAA (Federal Aviation Administration), an actual section of junction from airport “A”and a modified section of junction from airport“ A”. The vertical displacement of the asphalt surface caused by the horizontal displacement of the concrete pavement was investigated in the three types of junction. RESULTS: A vertical displacement of approximately 13 mm occurred for the FAA standard section under horizontal pushing of 100 mm, and a vertical displacement of approximately 55 mm occurred for the actual section of airport “A”under the same level of pushing. On the other hand, for the modified section from airport“ A”a vertical displacement of approximately 17 mm occurred under the same level of pushing, which is slightly larger than the vertical displacement of the FAA standard section. CONCLUSIONS: It was confirmed that shoving of the asphalt pavement at the junction could be reduced by placing the bottom of the buried slab on the top surface of the subbase. It was also determined that the junction type suggested in this study was more advantageous than the FAA standard section because it resists faulting by the buried slab that is connected to the concrete pavement. Faulting of the junctions caused by aircraft loading will be compared by performing finite element analysis in the following study.

PURPOSES: The purpose of this study is to suggest a specific investigation guideline to decide priority of repairing old concrete pavements that pile up substantially. METHODS : In this study, a principle of division of homogeneous sections was proposed to reflect the characteristics of the pavement reasonably in the specific investigation results. In addition, a checklist and guideline of field investigation were suggested for the old concrete pavement sections, which require inspection toward their durability and structural performance. Furthermore, the items of laboratory test necessary to the old concrete pavement were suggested based on the existing laboratory test considering characteristics of the old concrete pavement. The present condition of the old concrete pavement could be analyzed by the test results. RESULTS: A method of division of homogeneous sections suitable for the specific investigation of the old concrete pavement was suggested. The proportions of distress severity of pavement sections were compared by distress type to figure out the present state of the old concrete pavement. Scaling, durability cracking (or alkali-silica reaction), and longitudinal spalling were selected as the most severe distress types. The detailed positions of the sections were also suggested. The checklist of the specific investigation was categorized by field survey and laboratory test, and its evaluation criteria were proposed. The three types of the sections of durability cracking (or alkali-silica reaction), bridge connection, and asphalt overlay were selected as the sections of the field survey. The compressive strength, void structure, and chloride penetration depth were suggested as the items of the laboratory test. CONCLUSIONS : A fundamental level of the guideline was suggested in this study to resolve the problem of old concrete pavement. Appropriate guidelines related to the repair of the old concrete pavement should be provided by performing additional research efforts.

도로포장의 하부층은 시공당시 엄격한 다짐관리를 통해 시공되지만, 시간이 경과함에 따라 교통하중과 환경하중에 의해 포장하부의 품질이 저하되며 이는 도로포장의 공용성에 영향을 미친다.(박주영 등, 2012). 또한, 최근 지구온난화에 따른 이상기후로 인해 겨울철 한파가 증가하는 추세이며(기상청, 2012), 이는 포장하부층의 지반 동상과 관련하여 동결융해가 반복됨에 따라 포장하부의 지지력이 저하되고 이에 따라 도로포장의 파손이 발생된다. 이러한 악조건 속에서 포장의 파손 빈도는 급증하는 추세이며, 이에 따라 국내에서는 도로의 유지보수 및 관리에 대한 중요성이 대두 있고, 따라서 포장하부의 상태를 체계적으로 관리하고 적절한 유지보수 시기를 결정함으로서 포장의 공용성을 향상시키는 것은 매우 중요하다.포장하부의 상태를 평가하는 기법으로는 FWD(Falling Weight Deflectometer)가 존재하는데, FWD는 포장체에 하중을 재하 하여 발생되는 처짐값을 여러개의 지점에서 측정하여 하중과 처짐값의 상호관계를 이용하여 포장하부 상태를 평가한다. 또한 측정된 값을 AASHTO의 AREA 방법을 사용하여 포장의 강성을 나타내는 상대강성반경과 지지력계수를 역산할 수 있다. 일반적으로 포장하부 상태평가 시 이동식 차량 FWD를 사용하는데 현재는 차량의 진행방향에 대해서만 포장하부 상태평가를 실시하고 있는 실정이다. 하지만 동일 지점을 차량 진행방향의 반대 방향으로 포장하부를 평가할 경우 동일 지점이라 하더라도 처짐값 측정기의 위치가 달라지고, 이에 따라 상대강성반경과 지지력계수의 차이가 FWD의 측정 방향에 따라 발생하게 된다. 하지만 FWD를 양방향으로 분석하는 기법은 없으며 방향에 따른 포장하부상태의 차이가 존재함에도 불구하고 이에 대한 명확한 지침이 또한 없는 상태이다. 따라서 본 논문에서는 FWD의 진행방향에 따른 포장하부 상태를 평가하였다. 이를 위해 유한요소해석 프로그램인 ABAQUS를 사용하여 하중에 따른 처짐값을 양방향에 대해 측정하였고, 측정된 값을 사용하여 방향에 따른 상대강성반경과 지지력계수의 차이를 분석하였다. 또한 포장하부의 지지력계수 변화에 따른 상대강성반경의 변화를 양방향에 대하여 분석하였고, 이어 포장하부에 공동을 모사하여 공동의 크기와 지지력계수의 변화에 따른 상대강성반경의 변화를 분석하였다.