Backcalculation Program Research Articles

Proposing Binary Gravitational Search Algorithm Parameters for Back-calculation of Road Pavement Moduli

A Falling Weight Deflectometer is popular equipment to measure surface deflections under imposed loadings, providing the necessary parameters for back-calculating the elastic moduli of road pavements. There are several back-calculation programs available that accurately back-calculate pavement layer moduli. The Gravitational Search Algorithm (GSA), a metaheuristic optimization algorithm inspired by Newton’s law of universal gravitation, is one such algorithm. The Binary Gravitational Search Algorithm (BGSA) is an enhancement algorithm based on GSA that can be used as an efficient search algorithm for back-calculating pavement moduli based on matching measured and calculated surface deflection of road pavements. Choosing the best BGSA parameters is critical for accurate back-calculation of road pavement moduli. Nevertheless, there has not been much study on selecting the best BGSA parameters for back-calculating road pavement moduli in the literature. Therefore, this study proposes strategies for selecting BGSA parameters based on the least computational effort and the least root mean square error between measured and calculated road pavement surface deflections. In this study, the Burmister theory is discussed and the Richardson extrapolation is adopted to improve the accuracy of the calculated points near the pavement surface; the best parameter of BGSA including the agent size A of 50 and an iteration step T of 300 are suggested to back-calculating the road pavement moduli.

ANALISIS PREDIKSI KERUSAKAN PERKERASAN LENTUR BERBASIS IRI (INTERNATIONAL ROUGHNESS INDEX) DENGAN METODE IRMS-V3, RONET

The condition of road pavement is going to decrease during its service life. To keep a pavement functioning, maintenance must be continuously performed. However, the maintenance that has been carried out so far has not been carried out optimally because the budgeting system is still carried out annually based on the results of a road condition survey. The preparation of the budget is carried out annually by BBPJN SUMUT as the relevant stake holder, based on the FWD value with a back calculation program. This causes funding to become unsustainable so that it affects unsustainable handling as well. There are several methods for calculating predictions of future damage values ​​including IRMS-V3 and RONET. Both have a basis for calculating the value of IRI as the main variable in predicting damage. The purpose of this study is to use both methods and compare them to predict IRI values, traffic growth values, and also the remaining planned life values ​​in order to obtain a funding/budget planning scheme and the right type of treatment. The type of data used is secondary data sourced from North Sumatra BBPJN. The analysis is carried out by calculating the IRI value, traffic volume, and the remaining planned life for the next 5 years. Based on the results of the analysis obtained, road damage will occur more quickly using the RONET method. Road maintenance funds resulting from the IRMS-V3 method are more economical. Then validated using statistical t test. The results show that there is no difference in the average predicted IRI value, but there is a difference in the average predicted RSL value for the two methods

Influence of Seed Layer Moduli on Backcalculation Procedure and on Overlay Design of Flexible Pavements

The seed moduli selected for backcalculation analysis of multilayer flexible pavement can have significant effects on the performance of backcalculation software and, sometimes, the final solutions of the overlay designs. Therefore, this paper aims to analyze the variability of the resilient moduli (MR) obtained by backcalculation programs, taking different seed moduli as input data. To this end, data obtained from non-destructive structural evaluation (falling weight deflectometer [FWD]) were used in three different regions of Brazil. Thereafter, the deflection basin values and the seed moduli were inputted into the two backcalculation methods: linear elastic and finite element. By varying the RM seed of one of the layers by 100%, the percentage differences in the backcalculated moduli were computed within the range of typical resilient modulus (MR) values for paving materials, and close to the upper and lower thresholds of the usual moduli in Brazil. Furthermore, with the data provided by backcalculation software and crack monitoring, these were inputted into the flexible pavement design software (MeDiNa) to also analyze the influence of the seed moduli variability on the pavement overlay design, through the cracked area percentage parameter. Therefore, it was found that the seed moduli have a high influence on the backcalculated moduli, with percentage differences of up to 68.30%, mainly for the base and subbase layers of pavement. Even with the differences obtained in the values of the backcalculated moduli, it was found that the seed moduli did not cause a significant impact on the overlay design in which the percentage difference between the cracking predicted for the surface layer was less than 2.5%.

Structural Characterization of Fractured Portland Cement Concrete Pavements in Pennsylvania from Falling Weight Deflectometer Data

Hot mix asphalt (HMA) overlays on fractured Portland cement concrete (PCC) is a common rehabilitation alternative used for PCC pavements in Pennsylvania. Several fracture techniques including rubblization, crack and seat (C&S), and break and seat (B&S) have been used for decades to minimize reflective cracking by reducing the effective slab length and, with it, expansion/contraction movement. The design of this type of overlay requires knowledge of the structural capacity of the fractured PCC layer. The AASHTO 93 and Pavement ME design methods are used by the Pennsylvania Department of Transportation (DOT). These methods and the Pennsylvania DOT documentation recommend certain values to characterize the structural capacity of the fractured PCC. However, the guidance envisaged the selection of these values provided by these design methods and the Pennsylvania DOT documentation is limited. The objective of this study is to determine realistic Pennsylvania-specific elastic modulus (EPCC) values and layer coefficients (LC) to characterize the in situ behavior of fractured PCC layer for jointed reinforced concrete pavements (JRCP) and jointed plain concrete pavements (JPCP). To obtain these structural properties, 11 different rehabilitation projects located in Pennsylvania were analyzed using falling weight deflectometer (FWD) data, backcalculation programs, and statistical methods. Based on this analysis, the recommended values of EPCC and LC for C&S overlay design are 360 ksi (kips per square inch) and 0.32, respectively. In the case of B&S overlay design, these values correspond to 400 ksi and 0.34, respectively. The variability of the slab fracturing process and the reduction of the structural capacity caused by fracturing were also analyzed in this investigation.

Asset management innovation for rigid pavements

Today, the new pavement management tools encourage preventive action, whereas more traditional approaches focus on acting on observed damage. An adequate initial evaluation is essential to properly manage pavement maintenance. In this regard, non-destructive tests such as deflection tests make it possible to obtain first-hand information without altering the condition of the pavement, and their use is becoming increasingly more common. This paper presents a study of the structural evaluation of rigid pavements based on measured deflections. Several aspects are identified which will make it possible to improve these procedures. A 62-kilometre stretch a motorway in Mexico has been used as a case study. A campaign of on-site measurements was carried out using a Falling Weight Deflectometer (FWD). The deflection values were used in several iterative methods with calculation programs and manual analytical methods, comparing the results obtained. The elastic moduli of the pavement layers were determined. These are the main parameters for calculating the remaining life of the structure, which facilitate decision-making around pavement management. The results obtained in this study demonstrate the usefulness of back-calculation methods for analysing the structural condition of rigid pavements as an initial stage in the development of pavement management systems. The conclusions validate the use of back-calculation programs in the structural analysis of rigid pavements, by comparing the results obtained with manual analytical methods.

A Comparison of Dynamic Soil Models for Backcalculation of Engineering Soil Properties from Falling Weight Deflectometer Data

The falling weight deflectometer (FWD) test is one of the most widely used nondestructive tests for backcalculation evaluation of pavement and soil properties. Despite the advantages in accounting for the time-dependent load and responses, the accuracy of evaluating elastic moduli based on dynamic backcalculation analyses is, however, significantly depended on the forward dynamic soil models employed in the backcalculation process. To serve this challenge, a comparison for advantages, limitations and the reliability of different dynamic soil models employed in the backcalculation of engineering soil properties is presented in this paper. Two types of dynamic soil forward models in the FWD backcalculation, namely, dynamic single-degree-offreedom (SDOF) and dynamic half-space models are considered. The study in this paper provides a better understanding of dynamic backcalculation processes which is essential for the development of dynamic backcalculation program and its applications.

Backcalculation of Flexible Pavement Layer Moduli from Traffic Speed Deflectometer Data

In the past few years, state transportation departments in the United States have been investigating the potential use of the traffic speed deflectometer (TSD) in routine network-level pavement structural evaluation, including efforts to compute parameters typically obtained with the falling weight deflectometer (FWD). However, differences in loading configuration (single plate versus dual tires) and mechanism (impact versus moving load) between the FWD and the TSD necessitate modification of conventional analysis methodologies for use with TSD data. The TSD is a trailer truck that uses Doppler lasers to measure the pavement deflection velocities at normal traffic speed. Deflection velocities are then converted to surface deflections with a computational algorithm. This study proposes two approaches to backcalculating layer moduli from the TSD data. The first method uses 3D-Move software and deflection velocities measured directly by the TSD. The 3D-Move software can closely simulate TSD loading by considering moving load, nonuniform contact pressure of the dual tires, and viscoelastic material properties of asphalt layers. The second method uses TSD-computed surface deflections in a linear elastic analysis backcalculation program modified to incorporate a dual-tire configuration. The two methods were evaluated with field data from the MnROAD test facility and two in-service pavement sections in Pennsylvania and Idaho. The results show that the second method can be reliably used in network-level applications until the first method becomes computationally practical. The limitations of use of the TSD deflection measurement in the conventional FWD backcalculation program was also demonstrated.

Dynamic Soil Models for Backcalculation of Material Properties from Falling Weight Deflectometer Deflection Data

Falling Weight Deflectometer (FWD) test is one of the most widely used methods for in-situ nondestructive evaluation of pavement/soil properties and examination of the structural condition of in-service pavements. A dynamic half-space model is employed in the present work for backcalculation of engineering soil properties from the FWD data. The advantages, limitations and the reliability of the backcalculation elastic moduli evaluated from dynamic soil model are discussed in this paper. Selected numerical results are presented to portray the influence of governing parameters, for example, the presence of shallow stiff layer and the mass density of soil material on dynamic backcalculation of the soil elastic modulus. The investigation presented in this study provides a better understanding of dynamic backcalculation processes which is essential for the development of dynamic backcalculation program and its applications.

Analysis on Relationship between FWD Back-calculated Modulus and Dynamic Modulus of Asphalt Layers for Existing Asphalt Pavements

PURPOSES: The objective of this study is to analyze the relationship between the FWD back-calculated modulus and dynamic modulus of asphalt layers for existing asphalt pavements. METHODS: To evaluate the dynamic modulus of the asphalt mixture in the existing and new asphalt layers, the uniaxial direct tension test was conducted on small asphalt specimens obtained from the existing asphalt-covered pavements. A dynamic modulus master curve was estimated by using the uniaxial direct tension test for each asphalt layer. The falling weight deflectometer (FWD) testing was conducted on the test sections, and the modulus values of pavement layers were back-calculated using the genetic algorithm and the finite element method based back-calculation program. The relationship between measured and back-calculated asphalt layer moduli was examined in this study. The normalized dynamic modulus was adopted to predict the stiffness characteristics of asphalt layers more accurately. RESULTS: From this study, we can conclude that there is no close relationship between dynamic modulus of first layer and back-calculated asphalt modulus. The dynamic moduli of second and third asphalt layers have some relation with asphalt stiffness. Test results also showed that the normalized dynamic modulus of the asphalt mixture is closely related to the FWD back-calculated modulus with 0.73 of R square value. CONCLUSIONS: The back-calculated modulus of asphalt layer can be used as an indicator of the stiffness characteristics of asphalt layers in the asphalt-covered pavements.

Backcalculation of Asphalt Concrete Modulus Master Curve from Field-Measured Falling Weight Deflectometer Data

A new backcalculation program, DYNABACK-VE, was used to backcalculate pavement layer properties with field data. DYNABACK-VE used a time domain viscoelastic dynamic solution (ViscoWave-II) as a forward routine and a genetic algorithm for backcalculation analysis. The genetic algorithm search method was selected because it had a high potential for converging efficiently to a global solution. The forward solution used continuous integral transforms (Laplace and Hankel) that were more appropriate for transient, nonperiodic signals in the time domain. The algorithm was implemented in C++ and coded for parallel processing with multithreading for achieving better computational efficiency. Field falling weight deflectometer load and defection sensor time histories from three sites (Waverly Road near Lansing, Michigan, and two long-term pavement performance sections) were used for validation. The backcalculated asphalt concrete modulus master curves were compared with those obtained from laboratory testing. Very good agreement was obtained. The new algorithm was capable of backcalculating reliably the master curve of the asphalt concrete layer (four sigmoidal coefficients and two time-temperature shift factors), the elastic moduli for the unbound base or subbase and subgrade materials, and the modulus of stiff layer and the depth to stiff layer, if present. The advantage of the new solution is that it can analyze the response of pavement systems in the time domain and can therefore accommodate time-dependent layer properties and incorporate wave propagation. Also, because the backcalculation is performed in the time domain, the algorithm is not sensitive to truncation in the deflection time histories. This is a significant improvement to the state of the art, since truncation of deflection time histories has prevented frequency domain backcalculation solutions from being successful when measured field data are used.

Significance of Subgrade Damping on Vehicle-Pavement Interactions

The falling weight deflectometer (FWD) produces pavement responses by a falling mass drop to evaluate structural parameters of the pavement. A reliable simulation model is helpful to calibrate the apparatus as well as the backcalculation programs. The key points in the finite element simulation of FWD tests were studied including model size, boundary conditions, and analysis time increment. The subgrade in the finite element model was formulated with springs of stiffness coefficient of subgrade and dashpots of the derived damping values. It was concluded that at least six times the radius of relative stiffness is required to avoid boundary cut-off error. A rigorous procedure is presented to derive subgrade reaction and damping for various types of subgrade soil. Subgrade damping plays an important role in simulations of the FWD test. Backcalculation programs without subgrade damping may over-predict structural condition of pavements.

Structural Characterization of Iowa’s Rubblized PCC Pavements

AbstractRubblization is considered one of the sustainable surface preparation techniques before placing a hot mix asphalt (HMA) overlay that involves breaking the concrete pavement into pieces. The design of the structural overlay thickness for rubblized projects is difficult as the resulting structure is neither a true rigid pavement nor a true flexible pavement. The most important aspect of the design procedure is to characterize the rubblized concrete layer in terms of a layer coefficient and modulus for the empirical and the mechanistic-empirical (M-E) pavement design methods. This paper describes a field study undertaken to investigate the performance of rubblized pavements in Iowa, which includes characterization of the rubblized Portland cement concrete (PCC) layer (layer coefficient and modulus) using a neural networks-based layer moduli backcalculation program. The average rubblized PCC layer coefficient and backcalculated modulus of the rubblized layer in Iowa were found to be 0.19 and 539 MPa (...

An improved dynamic model for the study of a flexible pavement

This paper introduces the semi-analytical and finite element models implemented to study a Falling Weight Deflectometer test conducted on a flexible pavement. These dynamic models take into account the effects of both Rayleigh damping in soil and viscous damping in bituminous materials, with respect to temperature, on structural deflection. Moreover, numerical results have been compared with in situ measurements recorded on an instrumented pavement. Results from numerical models showed the importance of taking into account the effect of damping (hysteretic or viscoelastic) of all layers of the pavement against temperature, loading and mechanical parameters. The parametric analysis introduced as a basis for future development of a dynamic backcalculation program.

Application of Genetic Algorithm and Finite Element Method for backcalculating layer moduli of flexible pavements

The backcalculation program, GAPAVE, which uses the Genetic Algorithm (GA) and Finite Element Method (FEM), is developed to predict the layer moduli from Falling Weight Deflectometer (FWD) deflections. The use of the FEM in the forward calculation that incorporates the GA improves the accuracy in backcalculating the pavement layer moduli. The optimum GA parameters are selected from sensitivity analysis for six different pavement structures. It is found that the use of optimal GA parameters suggested from this study can improve the prediction quality in backcalculating the pavement layer moduli. FWD deflection data and resilient modulus test data obtained from the Long-Term Pavement Performance (LTPP) database are used to evaluate the performance of the GAPAVE program. Backcalculated layer moduli for the asphalt concrete and foundation layers are compared against the resilient moduli obtained from laboratory testing. The validation results indicate that GAPAVE with the optimal GA set of parameters can effectively estimate the actual stiffness characteristics of the pavement materials.

Field Verification of Superpave Dynamic Modulus

In the mechanistic-empirical pavement design guide, prediction of flexible pavement response and performance needs an input of dynamic modulus of hot-mix asphalt at all three levels of hierarchical inputs. This study was intended to find the best way to predict/derive this input. Nine Superpave pavement sections were selected as test sections in this study. Deflection data on all test sections was collected with a Dynatest 8000 falling weight deflectometer shortly after construction. The deflection data, normalized with respect to 40-kN load, were used to back-calculate asphalt layer moduli using three back-calculation algorithms. Laboratory dynamic modulus tests were conducted on asphalt concrete (AC) cores and laboratory-compacted samples. Dynamic modulus was also estimated with the Witczak model, new Witczak model, and Hirsch model. The results show that the AC moduli obtained from various back-calculation programs used in the study are generally comparable. Laboratory dynamic modulus is comparable at 4°C, but the variation increases as the test temperature increases. The Witczak model underestimates the dynamic modulus at low temperature and overestimates it at higher temperature. The parameter estimate when the laboratory dynamic modulus is used as a dependent variable and the moduli from other approaches as independent variables is close to 1. This is especially true for the AC moduli estimated by various prediction methods. The Hirsch model appears to be the best for estimation and is closely followed by the new Witczak model.

Evaluation of layer properties of flexible pavement using a pseudo-static analysis procedure of Falling Weight Deflectometer

Most backcalculation programs used to evaluate the pavement layer properties assume static deflections even though dynamic deflections are generated from the Falling Weight Deflectometer (FWD). This study aims to take into consideration the dynamic effects of the deflection basin from the FWD in the backcalculation procedure. A Pseudo-static backcalculation procedure, named DYN-BAL (Dynamic BALMAT), was developed to calculate the layer moduli after converting dynamic deflections into static deflections. In situ tests were carried out to evaluate the applicability and reliability of the backcalculation procedure, which can accommodate the dynamic effect. In situ tests included FWD tests at the site of a Multi-Depth Deflectometer (MDD) installation. From the test results, it was found that DYN-BAL gives the most reliable results when compared with several other computer codes in use.

CalBack: Enhancing Caltrans Mechanistic-Empirical Pavement Design Process with New Back-Calculation Software

In 1996, California Department of Transportation (Caltrans) initiated an extensive project to develop mechanistic-empirical (ME) pavement design and analysis tools, which will help state design engineers incorporate the impact of new products and technologies, increased traffic volumes and axle loading, and variable climatic conditions. As part of the development of new ME design procedures, Caltrans is developing a suite of dedicated software. CalME is a ME design program for flexible pavements that parallels the NCHRP 1-37A (MEPDG) and is calibrated for California conditions. CalBack is a sophisticated back-calculation program that contains specific features pertinent to California and is designed to work standalone, or in concert with CalME. CalBack is a unique and important addition to the existing knowledge base in that it possesses multiple data input/output methods, several new analytical modeling methods, and numerous user performance options. This paper describes the successful development and implementation of CalBack in three ways: (1) why and how Caltrans developed CalBack; (2) how CalBack functions; and (3) representative studies that show how well the software performs. Application of CalBack in several California projects, including the case studies presented in this paper, has shown that back-calculated moduli for different layers in the flexible and rigid pavement systems agreed reasonably well with laboratory measured values. Furthermore, the importance of avoiding temperature gradients when evaluating portland cement concrete pavements with the falling weight deflectometer is also well captured by CalBack.

A comparative study on measured vs. Predicted pavement responses from falling weight deflectometer (FWD) measurements

Falling weight deflectometer (FWD) drops were applied on the entire 24 test sections, and the resulting surface deflections were measured simultaneously using FWD geophones. The MODULUS 4.0 backcalculation program developed by the Texas Transportation Institute (TTI) was used to backcalculate the asphalt concrete layer moduli values of each test section. then the backcalculated moduli values were entered into a forward calculation program, WES-5, with known pavement layer thicknesses, assumed Poisson's ratio, and the magnitude and geometry of FWD loading to calculate the surface and depth deflections. The surface and depth deflections were used to calculate the average vertical strains of different layers at the centerline of loading. In the validation process, the comparisons between the measured and predicted pavement responses were made.

Seed Modulus Generation Algorithm for Backcalculation of Flexible Pavement Moduli

The seed moduli chosen for backcalculation analysis of multilayer flexible pavements can have significant impacts on the performance of backcalculation software and, sometimes, the final solutions of the backcalculated moduli. Practically all backcalculation programs provide internally generated seed moduli for backcalculation analysis. However, as the internally generated seed moduli do not always produce satisfactory results, the use of user-input seed moduli is generally encouraged. With the aim of providing useful guidance in the choice of seed moduli, a seed modulus generation algorithm, 2L-BACK, for multilayer flexible pavements based on a closed-form modulus backcalculation solution for two-layer flexible pavement structures was developed. The proposed algorithm does not require any subjective judgment by the user. An evaluation analysis of the effectiveness of the proposed procedure is presented by the use of two types of backcalculation software, MICHBACK and EVERCALC, and is based on measured and computed data for flexible pavement segments from the Long-Term Pavement Performance project. A comparison was made of the backcalculation program performance and the computed moduli of solutions obtained from internally generated seed moduli and those obtained from seed moduli generated by the proposed algorithm. It was found that the proposed seed modulus generation algorithm led to enhanced program performance of MICHBACK with respect to convergence characteristics and the accuracies of the backcalculated solutions. In comparison, the corresponding improvements for the case of EVERCALC were less. The proposed seed modulus generation algorithm does not suffer from the location and pavement type transferability constraints of most regression-based seed modulus generation methods. The results of the study suggest that the algorithm can be effectively incorporated into backcalculation software for multilayer flexible pavements.

Seed Modulus Generation Algorithm for Backcalculation of Flexible Pavement Moduli

The seed moduli chosen for backcalculation analysis of multilayer flexible pavements can have significant impacts on the performance of backcalculation software and, sometimes, the final solutions of the backcalculated moduli. Practically all backcalculation programs provide internally generated seed moduli for backcalculation analysis. However, as the internally generated seed moduli do not always produce satisfactory results, the use of user-input seed moduli is generally encouraged. With the aim of providing useful guidance in the choice of seed moduli, a seed modulus generation algorithm, 2L-BACK, for multilayer flexible pavements based on a closed-form modulus backcalculation solution for two-layer flexible pavement structures was developed. The proposed algorithm does not require any subjective judgment by the user. An evaluation analysis of the effectiveness of the proposed procedure is presented by the use of two types of backcalculation software, MICHBACK and EVERCALC, and is based on measured an...