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Pavement performance studies are being conducted in the states of Nevada and Washington for the purpose of developing mechanistically based pavement design procedures for highways. A critical element of each of these studies is the statewide characterization of the pavement materials. The materials characterization process has included laboratory and field testing for 16 sites in Washington and 27 sites in Nevada.
The objective of this study is to develop a mechanistic-empirical 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 asphalt pavements that uses multi-load level FWD deflections has been developed using these relationships. The verification study was conducted using field data.
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.
This synthesis report will be of interest to pavement and geotechnical design and research engineers, geologists and engineering geologists, and related laboratory personnel. It describes the current practice for measuring in situ mechanical properties of pavement subgrade soils. The tests conducted to measure the mechanical properties of soil strength and stiffness are the primary topics, and these are discussed in the context of design procedures, factors affecting mechanical properties, and the variability of measurements. Information for the synthesis was collected by surveying U.S., Canadian, and selected European transportation agencies and by conducting a literature search. This TRB report provides information on existing and emerging technologies for static and dynamic, and destructive and nondestructive testing for measuring in situ mechanical properties of pavement subgrade soils. Correlations between in situ and laboratory tests are presented. The effects of existing layers on the measurement of subgrade properties, and soil spatial and seasonal variability are discussed. Most importantly, the use of soil properties in pavement design and evaluation are explained. New applications or improvements to existing test methods to support the use of mechanistic/stochastic-based pavement design procedures are also explained.
Structural evaluation can be very useful at the network level for project prioritization purposes. In the project priority ranking procedure of the Kansas Department of Transportation (KDOT), a pavement rating attribute, Pavement Structural Evaluation (PSE), is used. These ratings are subjective. his study outlines an approach based on the classical multiple regression analysis resulting in a better estimation of the PSE values using the results from the Falling Weight Deflectometer (FWD) tests and network-level distress survey. The regression models proposed in this study predict the decrease in PSE values by taking into account the FWD data, age, thickness, and distress levels of pavements, and very closely approximate the current PSE ratings obtained at the district level.
The objective of this study was to develop an approach for incorporating techniques to interpret and evaluate deflection data for network-level pavement management system (PMS) applications. The first part of this research focused on identifying and evaluating existing techniques, seeking out those that were simple, reliable, and easy to incorporate into current PMS practices, as well as those that produced consistent results. The second part of the research detailed the development of guidelines for the application of recommended techniques and procedures for determining optimum falling weight deflectometer (FWD) test spacing and data collection frequency. While there are many viable techniques available for evaluating the structural capacity of pavements that use FWD for project-level analysis, many of these techniques are time consuming and require an experienced analyst. As a result, using pavement deflection testing for network-level analysis has been limited to date. This guide provides information for the assessment of pavement structural performance for PMS applications. It reflects the general findings presented in the accompanying final report, Simplified Techniques for Evaluation and Interpretation of Pavement Deflections for Network-Level Analysis (FHWA-HRT-12-023).
This report describes the efforts undertaken to review the status of falling weight deflectometer (FWD) equipment, data collection, analysis, and interpretation, including dynamic backcalculation, as they relate to the models and procedures incorporated in the Mechanistic-Empirical Pavement Design Guide. The work conducted in this project resulted in the following: Development of a backcalculation scheme (BACKLAVA) in the time domain using a quasi-static model (LAVA) as its forward solution and genetic algorithm (GA) as its search engine. BACKLAVA is a backcalculation algorithm for a constant asphalt concrete (AC) layer temperature. Development of a backcalculation scheme (BACKLAVAP) in the time domain using a quasi-static model (LAVAP) as its forward solution and GA as its search engine. BACKLAVAP is a backcalculation algorithm for a temperature profile in an AC layer. Development of a backcalculation scheme (BACKLAVAN) in the time domain using a quasi-static model (LAVAN) as its forward solution and GA as its search engine. BACKLAVAN is a backcalculation algorithm for a viscoelastic AC layer and a nonlinear base layer. Development of a backcalculation scheme (DYNABACK-VE) in the time domain using a time-domain viscoelastic dynamic model (ViscoWave-II) as its forward solution and a hybrid approach (GA and Levenberg-Marquardt algorithm) as its search engine. DYNABACK-VE is a backcalculation algorithm for a viscoelastic AC layer with temperature profile and linear unbound layers. Short list of recommendations for FWD equipment enhancements. The tools developed in this project are standalone applications that could be used on most computers.