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When FWD tests are performed on broken or cracked pavements (of which information is crucial in making rehabilitation and overlay decisions), the multi-layered elastic theory-based backcalulation programs assume that the effect of these discontinuities in a cracked layer on deflection basins would be accounted for by the reduction of the elastic modulus for that layer. However, it has been concluded and confirmed by researchers and practitioners that the backcalculation algorithms based on the multi-layered elastic theory produce large variation in the algorithms based on the multi-layered elastic theory produce large variation in the 'effective' moduli of the cracked layers. Studies have also shown that significant errors in the backcalculated pavement moduli can accrue from performing a static analysis of what is inherently a dynamic test. Unfortunately, dynamic analysis usually involves complex calculations and requires significant computation time, thus making it impracticable for routine applications. This study presents a methology based on deflection basin parameters.
Good materials and construction practices are vital to producing high quality and long lasting pavements. Quality control and assurance techniques can provide the owner of the roadway the means to ensure that these desired ends are achieved. The objective of this research study is to determine whether the Falling Weight Deflectometer (FWD) can effectively be used to assist in the QC/QA process during pavement construction. The Long Term Pavement Performance (LTPP) study provided the data needed to accomplish this research. LTPP began, in about 1988, as the Strategic Highway Research Program (SHRP), and it included a subset of newly constructed or rehabilitated pavements called the Specific Pavement Studies (SPS). Some of these were targeted at pavement maintenance and rehabilitation, while others were for new construction. New construction was subdivided into three LTPP experiments, one for asphalt concrete (AC) surfaced pavements (SPS-1), one for Portland Cement Concrete (PCC) surfaced pavements (SPS-2), and one for both AC and PCC pavements under the influence of light traffic loads (SPS-8). In each case, several thickness and material designs were developed in an experimental design matrix. These SPS experimental design matrices were constructed under a variety of climatic conditions and material sources in several states. During construction of the SPS-1, -2 and -8 projects, a large number of field and laboratory tests were performed on each structural layer. These tests included densities, moisture contents, layer thickness measurements and others, along with FWD tests conducted at each layer interface. This report shows that the FWD data is of reasonable quality and certainly of sufficient quantity to carry out the research. The traditional test results, although not as extensive as FWD data, were also reasonable and appeared to cover most of the wide variety of pavement designs and construction locations represented by the LTPP/SPS database. Sixteen SPS-1, SPS-2 and SPS-8 test sites (each site represents between 2 and 12 test sections) were utilized for analyses during this research project. These sites represent a wide variety of materials, climates, and construction dates.
The objective of this study is to describe a mechanistic-empirical approach to developing an analysis method for assessing pavement layer conditions and estimating the remaining life of flexible pavements using multi-load level Falling Weight Deflectometer (FWD) deflections. A dynamic finite element program, incorporating a stress-dependent soil model, was developed to generate the synthetic deflection database. Based on this synthetic database, the relationships between surface deflections and critical pavement responses, such as stresses and strains in each individual layer, have been established. A condition assessment procedure for pavement layers using multi-load level FWD deflections is presented in this study. The results indicate that the proposed procedure can estimate the base and subgrade layer conditions. However, large variations were observed in the relationships between the DBCI and desg values and the subgrade CBR values for aggregate base pavements. A FWD test with a load of 53 kN or less does not result in any apparent nonlinear behavior of the subgrade in aggregate base pavements. With regard to the condition assessment of the asphalt concrete (AC) layer, the AC layer modulus and the tensile strain at the bottom of the AC layer are found to be better indicators than the deflection basin parameter. The procedures for performance prediction of fatigue cracking and rutting are developed for flexible pavements. The drastically increasing trend in fatigue cracking with time may not be predicted accurately using the proposed procedure. Such trends may be due to the environmental effects and the inconsistent distress measurements. Predicted rut depths using both single and multi-load level deflections show good agreement with measured rut depths over a wide range of rutting potential. However, the procedure using single load level deflections consistently underpredicts the rut depths. This observation demonstrates that the rutting prediction procedure usin.
As with the previous two symposia, the 32 papers from the June/July, 1999, Seattle symposium present advances in the nondestructive testing of pavements using conventional falling weight deflectometer techniques and other promising techniques such as ground penetrating radar, rolling weight deflecto
Principles of Pavement Engineering, Third edition is an essential reference on fundamental principles of pavement engineering, showing how to design, construct, evaluate and maintain pavements of all types.
The need to accurately characterize the structural condition of existing pavements has increased with the recent development, release, and ongoing implementation of the Mechanistic-Empirical Pavement Design Guide (MEPDG). A number of different material inputs are required in the procedure, and it is important to adequately characterize and define them. The analysis of deflection data collected by the falling weight deflectometer (FWD) provides a quick and reliable way to characterize the properties of the paving layers, as well as to assess the load-carrying capacity of existing pavement structures. With the release of the new MEPDG, there is a pressing need to identify and evaluate the way that FWD testing is integrated into the new design procedure. Moreover, as highway agencies continue to implement the MEPDG, they need best practices guidance on how to effectively test existing pavement structures and interpret the results as part of a mechanistic-empirical pavement evaluation and rehabilitation process.