The manufacturers of fwds can supply own backcalculation softwares. The falling weight deflectometer fwd test is the most commonly employed ndt, which simulates a load pulse induced by a truck moving at moderate speeds, and measures the deflections in the pavement using sensors radiating from a loading plate attached to the test device. Elmod analyzes the pavement response from the fwd and hwd by determining the modulus, stress and strain of each significant layer. Daps deflection analysis of pavement structures backcalculation of layer stiffness from deflection data using the singular value decomposition technique program installation the program is supplied on a single cdrom or via the internet. The pavement response is analyzed with dynatests elmod evaluation of layer moduli and overlay design software to determine the elastic moduli, stresses and strains of each modeled layer. Each available program has its own set strengths and weaknesses, and no two programs give exactly the same set of results. Collection of 7day 24hr traffic volume data to calculate new thickness as per irc372012 followed by axle load survey of 20% of the traffic volume collected and fwd test. Backcalculation can be made with softwares of other origin but usually the. Backcalculation is a mechanistic evaluation of pavement surface deflection basins generated by various pavement deflection devices.
The file should have the same root name as the fwd data file and would be normally located in the default directory c. With luck, the results of two different backcalculation programs may be close to one another. Development of method for backcalculation to estimate. Three temperature sensors, nine deflection sensors, a foursplit loading plate, a time history module, and warning lights are also supplied carl bro 2006. Back calculatio n moduli for different load levels cell 19 table iv. It reflects a change in the methods and procedures engineers use to design pavement structures by taking advantage of the advances in material mechanics, axleload spectra and climate data for. The disadvantage of the fwd method is that its results are often dependent on such factors as the particular model of tester used, the specific testing procedure, and the method of backcalculation. Various approaches and procedures for fwd deflection analysis have been developed in several studies xu et al. Software selection strategic highway research program. Fwd data is primarily used to estimate pavement structural capacity for 1 overlay design and 2 to determine if a pavement is being overloaded. Can someone suggest the software for back calculation of. Collection of existing crust details for calculation in kgp back software. Index backcalculation of layer parameters for ltpp test.
Flexible pavement evaluation by falling weight deflectometer. Note that the hma moduli is strongly related to the maximum fwd surface deflection, d 0, while the subgrade moduli is largely a function of fwd surface deflection at offsets greater than 914 mm 36 in. Apr 30, 2017 so, here is the back calculation of fwd data comes into place. Therefore, selection of the backcalculation software and procedures were confined to those that are based on the use of. Comparative study of static and dynamic falling weight. The rosy design, a backcalculation software for both road andor airport data analysis. Reliable pavement backcalculation with confidence estimation. Falling weight deflectometer fwd testing guideline. Older versions of the operating control software were written in microsoft dos. This is done via the creation of a construction information file. In 2008, a switch to microsoft windows based control software was made. The pavement layer stiffness determined through inverse analysis is a. Backcalculation of pavement structure characterization results.
Pavement properties are back calculated from the observed dynamic response of the pavement surface to an impulse load the falling weight. Aashtoware pavement me design is a productionready software tool to support the daytoday operations of public and private pavement engineers. The backcalculation process is usually iterative and normally done with computer software. The role of the fwd in the sofico campaign in wallonia.
The probabilistic approach to fwd back calculation, a relatively new approach, is initially introduced and a brief overview of its numerical implementation is presented. The driveroperator runs equipment from a laptop computer without the need of stepping out of. Structural evaluation of a dual twolane road by curviameter. Pavement properties are backcalculated from the observed dynamic response of the pavement surface to an impulse load the falling weight. Pavement construction information must be defined to enable back calculation. The first is the iterative approach in which a forward calculation scheme typically a linear elastic program is used within the iterative process chua, 1989. Most of these procedures and guidances for fwd deflection do not take account either the dynamic loading effect or nonlinear material behavior. However, files generated from the equipment can be applied in any other backcalculation program. Advanced tools such as monte carlo simulation and finite elements can enhance the depth and scope of pavement analysis and design calculations.
It is a trailermounted device that operates by dropping a weight on to the pavement and measuring the resulting pavement deflections. Load equivalency factors from the structural response of. The dynatest falling weight deflectometer fwd applies a dynamic load that simulates the loading of a moving wheel. This study was undertaken with the objectives of improving the accuracy and usability of iowa. The more commonly used fwd backcalculation software are listed below. Proceedings of the 2nd geomeast international congress and exhibition on sustainable civil. Mar 12, 2016 elmod 6 how to use elmod for backcalculation fwd. Utilizing the deflections measured by the fwd, the resilient moduli. The fem dynamic backcalculation attempted to estimate 12 unknown parameters, which are each layer youngs modulus, damping coefficient, and density. Daps deflection analysis of pavement structures is a rapid, accurate and reliable method for performing backcalculation of deflection results. The modulus of the subgrade can be converted into a subgrade rvalue. Comparison of static and dynamic backcalculation of flexible.
Schematic diagram of falling weight deflectometer the backcalculation process the purpose of back calculation is primarily to find out the insitu elastic moduli e of the different pavement layers. Net application compatible with all existing versions of. Backcalculation of pavement structure characterization results author. However, the predicted pavement layer moduli sometimes may not be accurate even if computed and measured deflection basin has fulfilled the standard and is in concurrence with certain. Giving great importance in supplying safe and stable equipment and the newest technology forms the basis of the fwd equipment. Interpretation of falling weight deflectometer data.
Systematic backcalculation protocol and prediction of. Schematic diagram of falling weight deflectometer the backcalculation process the purpose of backcalculation is primarily to find out the insitu. Rubicon toolbox is a suite of tools that can greatly increase the productivity of engineers involved with pavement rehabilitation design. Analysis software for our global fwd products jils in. Many of the backcalculation programs are limited by the number and thickness of the layers used to define the pavement structure but, more importantly, assume that the layers are linear elastic. This contribution illustrates possibilities and limitations of curviameter and fwd and difficulties encountered with back calculations from field data. Elmod reports the weakest layer of failure, residual life and determines the optimum. Different manufacturers use different data formats. Improving the accuracy and usability of iowa falling weight deflectometer data may 20 6. An obstacle to the use of tsd at the project level is that the standard approaches to back calculation of pavement properties are based on the falling weight deflectometer fwd. Several backcalculation methods have been developed for the flexible pavement. Theoretically and by instrument responses alexander kwasi appea abstract falling weight deflectometer fwd is currently used by most highway agencies to determine the structural condition of the highway network. Improving the accuracy and usability of iowa falling.
The common analysis method is to backcalculate material response parameters for each layer within the pavement structure from the fwd deflection basin measurements. Validation of fwd testing results at the virginia smart. Falling weight deflectometer fwd the falling weight deflectometer is a device that is used to evaluate pavement and pavement layer stiffness. The importance in supplying safe and stable equipment and the newest technology forms the basis of the fwd equipment. The fwd experiment is similar, but not equivalent, to the tsd experiment, and therefore it is not straightforward to apply the traditional fwd backcalculation. Net environment runs under windows xp, vista and win 7 2.
In this paper, the probabilistic approach to fwd backcalculation is used as a tool to investigate the reliability of different dynamic and static backcalculation procedures. To assess the trend in the structural deterioration of pavement the stiffness values can be. Backcalculation moduli for different load levels cell 16 table iv. Viscoelastic backcalculation of traffic speed deflectometer. Hwa provides data and engineering services for the design of pcc, hma and permeable pavement systems for residential, industrial, and airport use. Various computations may be performed on the deflection data to evaluate the pavement and the stiffness of it and its constituent layers. Hwa offers nondestructive pavement evaluation, subgrade assessment and moduli back calculation. Several back calculation methods have been developed for the flexible pavement. X j is the unknown variables, including modulus of elasticity, poissons ratio, thickness of layer, pressure, contact area, j varies from 1 to n.
The back analysis algorithm solves for both a two layer elastic system and the thickness of subgrade, or a three layer elastic system and the thickness of subgrade. The fwd experiment is similar, but not equivalent, to the tsd experiment, and therefore it is not straightforward to apply the traditional fwd back calculation. Both of numerical simulation data and insitu fwd load and deflection data are used to verify the accuracy of the backcalculated parameter values by fem dynamic backcalculation. In recent years, software has been developed to calculate aircraft pavement strength ratings from modulus values that are backcalculated from deflections measured by a falling weight deflectometer. Falling weight deflectomewter is a apparatus used for pavement evaluation civil engineering. Therefore, selection of the back calculation software and procedures were confined to those that are based on the use of elastic layer theory. The probabilistic approach to fwd backcalculation, a relatively new approach, is initially introduced and a brief overview of its numerical implementation is presented. Fwd testing has been an integral part of flexible pavements condition assessment for a decade. Viscoelastic or elastoplastic response programs have not been used in a sufficient number of projects to substantiate the reliability and adequacy of their use. Michback is a menudriven program which uses a modified newton method for the back calculation of flexible and composite pavement layer moduli, thicknesses, and stiff layer depth from measured surface deflections. So, here is the back calculation of fwd data comes into place. The software is written using modern windows programming languages with this version being developed for the windows 98 operating system. To assess the trend in the structural deterioration of pavement the stiffness values can be studied over a period of time. Equipment since 1994, the standard fwd device used at mnroad is the dynatest model 8000.
The backcalculation procedure is an iterative one, requiring several forward calculations. The company supplies their a rosy designa backcalculation software, but the fwd output may be used with other backcalculation packages. It illustrates the benefits of such investigations for a road administrator. Comparison of static and dynamic backcalculation of.
Note that the magnitude of fwd surface deflections decreases with increasing radial offsets and so does the relative accuracy of measurements. Chapter two falling weight deflectometer equipment. Deflection data from a uniform section of consistent runway pavement was analysed for variability to determine the effect of deflection variability. Ability to process a file in a batch mode can process any number of deflection records at a time exports batch calculation results into.
The following chapters in this ac present an overview of the ndt data collection process and equipment that are used to collect the field data. Chapter two falling weight deflectometer equipment falling. Falling weight deflectometer fwd testing has been used to evaluate structural condition of pavements to predict the layer moduli using backcalculation process. Can someone suggest the software for back calculation of falling weight deflectometer observations. The rosy design, a back calculation software for both road andor airport data analysis. This study aims to improve the accuracy and usability of iowa falling weight deflectometer fwd data by incorporating significant enhancements into the fullyautomated software system for rapid processing of the fwd data. Recently, a deflection analysis of pavement structures daps software has been developed, which enables the rapid calculation of layer stiffness moduli using a singular decomposition technique. The disadvantage of the fwd method is that its results are often dependent on such factors as the particular model of tester used, the specific testing procedure, and the method of back calculation. Mar 03, 2010 in this paper, the probabilistic approach to fwd back calculation is used as a tool to investigate the reliability of different dynamic and static back calculation procedures. Interpretation of falling weight deflectometer fwd data. The backcalculation software utilized shall be capable of providing the modulus of each pavement structure layer. However, files generated from the equipment can be applied in any other back calculation program.
Falling weight deflectometer the falling weight deflectometer fwd is a nondestructive testing device that has been widely used to evaluate pavement structural condition and strength of subgrade. Michback is a menudriven program which uses a modified newton method for the backcalculation of flexible and composite pavement layer moduli, thicknesses, and stiff layer depth from measured surface deflections. A big advantage of fwd testing is that it is fast and safe. Calibration improves the accuracy of pavement layer moduli derived from fwd data by means of backcalculation and other interpretive methods.
Generally, there are two groups of backcalculation programs. The deflection points measured by the fwd and the technical characteristics of the fwd the thickness of the different layers grip rating between the layers and poissons ratio estimation500400300200100 0800. Ac 150537011b, use of nondestructive testing in the. Evaluating falling weight deflectometer backcalculation software for aircraft pavement strength rating. Validation of fwd testing results at the virginia smart road. Calculation of vehicle damage factor using axle load data collected 5. Ability to switch application interface between english and metric. An obstacle to the use of tsd at the project level is that the standard approaches to backcalculation of pavement properties are based on the falling weight deflectometer fwd. Falling weight deflectometer fwd mndot pavement design. A falling weight deflectometer fwd is a testing device used by civil engineers to evaluate the physical properties of pavement. A basic flowchart patterned after lytton, 1989 1 that represents the fundamental elements in all known backcalculation programs is shown as figure 1. Falling weight deflectometer, fwd, pavement evaluation. Using back calculation of the fwd data we will get information about the insitu stiffness values for each individual layer quickly.
Backcalculation takes a measured surface deflection and attempts to match it to within some tolerable error with a calculated surface deflection generated from an identical pavement structure using assumed layer stiffnesses moduli. It reports the layer of failure and residual life by utilizing the lcca module which allows the user to select the optimum rehabilitation alternatives. Giving great importance in supplying safe and stable equipment and the. Evaluating falling weight deflectometer backcalculation. Dynamic analysis of falling weight deflectometer sciencedirect.
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