Falling Weight Deflectometer Device Research Articles

Falling weight deflectometer dispersion curve method for pavement modulus calculation.

The falling weight deflectometer (FWD) test is a common non-destructive testing method for evaluating the structural capacity of pavements. At present, data processing of the FWD test mainly focuses on the deflection data, while paying less attention to the deflection-time history. Because a FWD is equipped with impulse loads and geophones, which allow for the generation and capture of surface wave signal propagation, it is hypothesized that Rayleigh wave dispersion theory can be applied to calculate the modulus profile along the pavement depth by analysing the dispersive properties of the deflection signal measured during FWD tests. To test this hypothesis, we develop a new methodology for the FWD test and data analysis, referred to as the FWD dispersion curve method. We first introduce the concept of the new method, followed by an illustration of the procedure and the experimental set-up. Case studies on three concrete pavement segments are then presented to evaluate the effectiveness of the FWD dispersion curve method. Modifications to the existing FWD device are further recommended for the impact loading sources and signal collection process so that the modulus of a much shallower layer, such as the concrete slab and upper asphalt layers, can be obtained. This article is part of the theme issue 'Artificial intelligence in failure analysis of transportation infrastructure and materials'.

Prediction of remaining service life for flexible pavement in the Southern Central States using FWD parameters

Various Departments of Transportation (DOTs) in the South-Central States and abroad have extensively used Non-Destructive Testing (NDT) surface deflection bowl data. The primary purpose of using deflection-based NDTs in network-level assessment is to identify a section of pavement in need of further investigation at the project level. The falling weight deflectometer (FWD) test is a common NDT-based test that is used by transportation agencies to assess the performance of flexible pavement.This research concentrates on simulating the deflection produced by FWD devices using 3-D Move software. Simulations based on software will decrease the need for lengthy FWD testing in the field. In the study, ninety-seven (97) pavement sections from Arkansas, Louisiana, New Mexico, Oklahoma, and Texas are used for simulation, analysis, and verification of FWD testing. The deflection values produced from software simulations were found to be strongly correlated with field test findings. In addition, the simulated deflection values were used to develop and validate various deflection bowl parameters. In this study, the normalized comprehensive deflection ratio and the normalized comprehensive area ratio are two key characteristics that were validated and produced. Eventually, load-induced impacts using these parameters are effectively analyzed in order to anticipate the remaining service life of flexible pavement structures. The prediction of the remaining service life will be an efficient tool for different DOTs and transportation agencies to initiate the rehabilitation work in time and economically.

Prediction of remaining service life for flexible pavement in the Southern Central States using FWD parameters

Various Departments of Transportation (DOTs) in the South-Central States and abroad have extensively used Non-Destructive Testing (NDT) surface deflection bowl data. The primary purpose of using deflection-based NDTs in network-level assessment is to identify a section of pavement in need of further investigation at the project level. The falling weight deflectometer (FWD) test is a common NDT-based test that is used by transportation agencies to assess the performance of flexible pavement.This research concentrates on simulating the deflection produced by FWD devices using 3-D Move software. Simulations based on software will decrease the need for lengthy FWD testing in the field. In the study, ninety-seven (97) pavement sections from Arkansas, Louisiana, New Mexico, Oklahoma, and Texas are used for simulation, analysis, and verification of FWD testing. The deflection values produced from software simulations were found to be strongly correlated with field test findings. In addition, the simulated deflection values were used to develop and validate various deflection bowl parameters. In this study, the normalized comprehensive deflection ratio and the normalized comprehensive area ratio are two key characteristics that were validated and produced. Eventually, load-induced impacts using these parameters are effectively analyzed in order to anticipate the remaining service life of flexible pavement structures. The prediction of the remaining service life will be an efficient tool for different DOTs and transportation agencies to initiate the rehabilitation work in time and economically.

Comparison of Unbound Granular Materials’ Resilient Moduli Determined by Cyclic Triaxial Test and Innovative FWD Device

In addition to the conventional laboratory tests of input materials and construction mixtures, the technically correct design of pavement structure involves more frequent functional tests of the input materials and mixtures. Our study summarizes findings from a long-term monitoring of pavement on selected road sections with lower traffic intensity. The research involved the comparison of resilient moduli as a design parameter of unbound pavement base layers’ unbound granular materials (UGMs), determined in a laboratory by a test device for a cyclical triaxial test and in situ by impact load test using a falling weight deflectometer (FWD). In particular, the resilient moduli determined in the laboratory by a cyclic triaxial test (Mr,CTT) were compared with the real values of resilient moduli measured by FWD (Mr,FWD). A new, unique, and innovative FWD device was used to determine the Mr,FWD of the UGMs. The innovation lay in the dual-axis deflection measurement—measurement performed not just in the axis parallel to the road, but also in the axis in the transversal direction. It was found that, especially on roads with lower traffic load, such dual-axis (spatial) determination of Mr,FWD moduli was of great importance because it often allowed the identification of local pavement sections with low bearing capacities, especially at the edges, which have a significantly lower value of Mr,FWD.

Analiza asfaltnih kolničkih konstrukcija na temelju podataka strukturalne nosivosti

Ocjena strukturalnog stanja kolnika definira ukupnu nosivost kolnika, a određuje se kroz ocjenu mehaničkih svojstava slojeva kolničke konstrukcije. Defleksija predstavlja elastičnu deformaciju kolničke konstrukcije i jedan je od važnih pokazatelja strukturalne nosivosti kolnika. Iznos defleksije moguće je utvrditi teorijski, korištenjem zakonitosti teorije elastičnosti i poznavanjem materijalnih svojstava kolničke konstrukcije, ili empirijski, mjerenjem elastične deformacije generirane poznatim statičkim ili dinamičkim opterećenjem na površini kolnika, najčešće korištenjem uređaja s padajućim teretom (FWD uređaj). U ovom radu opisane su teorijske metode za određivanje strukturalne nosivosti kolničke konstrukcije, s naglaskom na defleksiju kao prevladavajući tehnički parametar za utvrđivanje ocjene strukturalnog stanja kolnika. Opisan je empirijski postupak utvrđivanja defleksije FWD uređajem te je dan pregled utjecajnih činitelja na izmjerene iznose defleksije. Prikazani su indeksi proizašli iz mjerenja defleksije, koji se koriste za utvrđivanje strukturalne ocjene kolnika. Na primjeru analize stanja kolničke konstrukcije provedene u sklopu diplomskog rada prikazana je važnost provedbe kontinuiranog mjerenja u svrhu utvrđivanja strukturalnog stanja i ocjene kolničke konstrukcije.

Premature Failure of Apedwa-Bunsu Junction Section of N6 in Ghana: Some Notes for Consideration

This study investigated premature and continual failure of the Apedwa-Bunsu Junction section of Route N6 in Ghana despite an earlier maintenance intervention which included geotextile installation and placement of a new wearing course. It involved a condition survey, density, asphalt content, gradation, stiffness modulus and Falling Weight Deflectometer (FWD) tests on the section. The condition survey revealed cracking (alligator, transverse and longitudinal), ravelling, potholes, rutting and shoving as the predominant defects on the road. The density tests on the bituminous layers revealed relative compaction levels which, in most cases, did not meet the minimum required by the technical specifications despite the additional densification by traffic. The poor compaction was corroborated by high pavement deflections from the FWD device. Asphalt cores revealed a friable dense bituminous macadam (DBM) layer although bitumen extraction tests indicated all design asphalt contents were met. Lack of inter-particle cohesion within the DBM layer was suggestive of stripping damage to the asphalt concrete. Some samples of the crushed rock base contained plastic fines and fines content that exceeded specification limits. High stiffness modulus values of the bituminous layers suggested possible premature aging of the asphalt binder which probably accelerated crack development. An earlier intervention in the form of placement of geotextile in the wearing course failed to arrest cracking because the material had been placed at a shallow depth rendering it ineffective. It was concluded that inadequate compaction of the bituminous layers and the use of crushed rock and other pavement materials that did not wholly meet the technical specifications were the root causes of the premature failure of the section.

Evaluation of the Traffic Speed Deflectometer Data Using Simplified Deflection Model

Falling Weight Deflectometer (FWD) has been used by many road agencies worldwide for structural evaluation of both flexible and concrete pavements since the 1980s. With the development of Traffic Speed Deflectometer (TSD), the laser-based deflectograph is increasing used to perform continuous bearing capacity measurement at a range of driving speeds. The two main advantages of the TSD technology are; its ability to carry out continuous deflection measurements rather than at discrete points and the tests can be carried out at traffic speed without the need for lane closure in the case a stationary device such as the FWD. The objective of this paper is to study the deflection basins generated by TSD on flexible pavements using Simplified Deflection Model (SDM). The study shows that TSD data can be modelled accurately using SDM that can be represented in a mathematical form of Y = K1exp (-r/K2). K1 is equal to deflection at D0 in micron and K2 is the structural parameter at the respective sensor location r. It is observed that the majority of the pavement sections possess nonlinear subgrade behaviour in the TSD deflection data. The dynamic effects generated by the TSD axle load are likely to be the reason for the pavements to exhibit subgrade nonlinearity. A comparison between the FWD and TSD data shows a high level of correlation and a mathematical model has been established for estimation of FWD deflections using the TSD data. The study also shows that he theoretical deflections generated by the SDM are in good agreement with the actual deflection data obtained from FWD test. Statistical analysis confirms that the SDM generated D0 deflections are not significantly different from the D0 deflections recorded by FWD device.

Backcalculation of Flexible Pavement Structural Properties Using a Restart Covariance Matrix Adaptation Evolution Strategy

AbstractMonitoring structural integrity of pavements is a central task of pavement management systems toward needs analysis and the subsequent design, prioritization, and optimization of pavement maintenance and rehabilitation projects. Nondestructive testing (NDT) methods, including falling weight deflectometer (FWD), are the most widely used monitoring approach. The FWD device creates an impulse load on the pavement surface, and the resulting pavement surface deflections are captured using geophones at a number of distances from the load. Various backcalculation methods have been proposed to calculate pavement structural properties from FWD surface deflection measurements. However, no unique technique has proved to yield a globally optimum solution to this complex, nondifferentiable problem. This study explores development of an effective and reliable backcalculation strategy with attention to variable layer thicknesses. A synthetic database of typical three-layer flexible pavement structures is created...

Dynamic Characterization of a Truss Bridge by Falling Weight Deflectometer

Several full-scale testing methods can be used to characterize and evaluate the global performance and condition of a bridge. These global methods consist of mainly static load tests and dynamic tests that use controlled or uncontrolled dynamic excitation. Each approach has advantages and disadvantages for experimental and logistical considerations, data analysis requirements, and scope and utility of the characterization results obtained. This paper presents a global dynamic characterization program based on controlled impact dynamic testing that was applied to a truss bridge. The impact testing was performed with a hand-held impact hammer and a falling weight deflectometer (FWD) as dynamic excitation sources. The objective of the project was to evaluate whether the FWD, which could produce a broadband dynamic force, could be an effective tool for the quantitative characterization of bridge performance and condition. Many transportation agencies already use FWD devices for their pavement evaluation programs, and it follows that if the device is suitable for the impact dynamic testing of bridges, then agencies also can use FWDs to evaluate bridges quantitatively. Dynamic testing approaches are discussed, and an impact dynamic testing program executed for the truss bridge is presented. The results obtained with the two dynamic excitation devices are presented and compared with each other and with the results from an analytical model of the bridge. Finally, several observations and conclusions related to the efficacy of FWD devices for the impact dynamic testing of bridges are presented and discussed.

Falling Weight Deflectometer Correlation

The falling weight deflectometer (FWD) is commonly used to perform project-and network-level structural evaluations. Some highway agencies perform network-level FWD testing as a part of their pavement management systems to assess in situ structural capacity, remaining service life, and current rehabilitation needs. Through prediction models, future condition and needs are also estimated. In contrast, project-level FWD testing is typically performed as part of the rehabilitation design process. Calibrated FWD equipment provides repeatable data for a pavement section (i.e., data obtained with the same unit, at the same location, and under similar conditions). However, different FWD devices manufactured by the same or different manufacturers do not necessarily provide similar deflection basins when they test the same section, even if they are calibrated. This paper summarizes the results of a study performed for the New Jersey Department of Transportation to assess the differences among the FWD devices available in New Jersey and to correlate the results obtained with the different devices. Two rounds of testing were performed on flexible and rigid pavement sections located in the FAA William J. Hughes Technical Center in Atlantic City. The first testing cycle was performed in November 2002, and the second was performed in May 2004. The analysis results indicate that significant differences in repeatability and reproducibility may exist between different FWD devices.

Falling Weight Deflectometer Correlation

The falling weight deflectometer (FWD) is commonly used to perform project- and network-level structural evaluations. Some highway agencies perform network-level FWD testing as a part of their pavement management systems to assess in situ structural capacity, remaining service life, and current rehabilitation needs. Through prediction models, future condition and needs are also estimated. In contrast, project-level FWD testing is typically performed as part of the rehabilitation design process. Calibrated FWD equipment provides repeatable data for a pavement section (i.e., data obtained with the same unit, at the same location, and under similar conditions). However, different FWD devices manufactured by the same or different manufacturers do not necessarily provide similar deflection basins when they test the same section, even if they are calibrated. This paper summarizes the results of a study performed for the New Jersey Department of Transportation to assess the differences among the FWD devices available in New Jersey and to correlate the results obtained with the different devices. Two rounds of testing were performed on flexible and rigid pavement sections located in the FAA William J. Hughes Technical Center in Atlantic City. The first testing cycle was performed in November 2002, and the second was performed in May 2004. The analysis results indicate that significant differences in repeatability and reproducibility may exist between different FWD devices.