摘要 :
The pavement engineering community is moving toward design practices that use mechanistic-empirical (M-E) approaches to the design and analysis of pavement structures. This effort is embodied in the Mechanistic-Empirical Pavement ...
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The pavement engineering community is moving toward design practices that use mechanistic-empirical (M-E) approaches to the design and analysis of pavement structures. This effort is embodied in the Mechanistic-Empirical Pavement Design Guide (MEPDG) that was developed over the last several years through the National Cooperative Highway Research Program (NCHRP) and accompanying AASHTOW are Pavement ME Design? software. As ALDOT moves toward implementation of M-E pavement design, the need to evaluate the effects of differences among the many types of traffic data on pavement design became apparent. This research project examined the differences among national-level traffic inputs developed through the aforementioned NCHRP studies (and now included as the default traffic data in the Pavement ME Design? software), state-level traffic inputs developed from data collected at ALDOT’s weigh-in-motion (WIM) sites, and site-specific data. The full range of traffic inputs considered in the M-E design process was divided into 13 groups; the effects of the three levels of data were evaluated separately for each group. A rational, unbiased, quality control procedure for ALDOT WIM data was developed and applied to the data. Traffic inputs at levels 1 (national), 2 (state or regional), and 3 (site-specific), as specified in the design software, were then developed. The sensitivity of the pavement thickness required to not exceed a specified set of allowable pavement distresses, for both flexible and rigid pavements, to different levels of traffic data in Alabama was then determined. Finally, axle load spectra recommendations for flexible and rigid pavement design were made for future use by ALDOT.
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摘要 :
Pavement engineers have been producing long-lasting hot-mix asphalt (HMA) pavements since the 1960s. Research has shown that well-constructed and adequately designed flexible pavements can perform well for extended periods of ti...
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Pavement engineers have been producing long-lasting hot-mix asphalt (HMA) pavements since the 1960s. Research has shown that well-constructed and adequately designed flexible pavements can perform well for extended periods of time (1). Many of these pavements in the past forty years were the products of full-depth or deep strength asphalt pavement designs, and both have design philosophies that have been shown to provide adequate strength over extended life cycles (2). Full-depth pavements are constructed by placing HMA on modified or unmodified soil or subgrade material. Deep strength pavements consist of HMA layers on top of a thin granular base. Both of these design scenarios allow pavement engineers to design thinner pavements than if a thick granular base were used. By reducing the potential for fatigue cracking and containing cracking to the upper removable/replaceable layers, many of these pavements have far exceeded their design life of 20 years with minimal rehabilitation; therefore, they are considered to be superior pavements (2). Inferior pavements are pavements that exhibit structural distresses, such as fatigue cracking and rutting (1), before their design life is achieved. The successes seen in the full-depth and deep strength pavements are the results of designing and constructing pavements that resist these detriments to the pavement’s structure. In recent years, pavement engineers have begun to introduce a methodology of designing pavements to resist the two main pavement distresses seen on roadways, and with this change in thinking has come the idea of perpetual pavements or longlasting pavements.
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Mechanistic-empirical (M-E) pavement design and analysis have recently made great strides toward widespread implementation in the United States. While some see this design methodology as a new concept, there are currently M-E pa...
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Mechanistic-empirical (M-E) pavement design and analysis have recently made great strides toward widespread implementation in the United States. While some see this design methodology as a new concept, there are currently M-E pavement design methodologies being practiced across the country (1, 2, 3, 4). As the new M-E Pavement Design Guide (MEPDG) is being completed and implemented, more attention is being spent on proper material and pavement response characterization (5). To determine theoretical load-induced responses in pavement structures using the M-E design framework, a pavement structure’s material properties are needed. The resulting mechanistic responses are then coupled with Miner’s Hypothesis (6) and transfer functions to predict pavement life. Transfer functions rely on theoretical strains and pressures to estimate the design life of pavement structures. If these theoretical pavement responses are accurately estimated, the transfer functions allow engineers to design a pavement of adequate thickness. It should be clear as the reader reads this report that this is not talking about the accuracy and precision of stain gauges for a given loading condition. The precision and accuracy include wander, pavement thickness, and other issues besides the accuracy and precision of the strain gauges. So the precision and accuracy are really for strain gauge measurements under somewhat varying conditions. As instrumentation and computing technologies have advanced, it has become possible to measure stresses, pressures, deflections, moisture, temperature, and wheel wander in pavements using embedded instrumentation instead of utilizing computer programs to estimate them (7). When actual measurements from pavement structures are used in transfer functions, the results are threefold. First, the design life of the pavement structure will be more accurately quantified. Second, the transfer functions used to estimate design life can be calibrated and validated using actual field data to improve the design procedure. Last, and perhaps most importantly, field measurements can aid in the refinement and development of theoretical models
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摘要 :
Since the inception of pavement design processes, engineers have been searching for ways to increase the life of their structures. Not only would a stronger and longer-lasting pavement be more economical for its owner, but it wo...
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Since the inception of pavement design processes, engineers have been searching for ways to increase the life of their structures. Not only would a stronger and longer-lasting pavement be more economical for its owner, but it would also reduce the ever growing dilemma of congestion on highways due to rehabilitation services being performed on the structure. With reduced rehabilitation comes a reduced delay on the structure’s users. From these needs has arisen the idea of creating a perpetual pavement. The Asphalt Pavement Alliance (APA, 2002) defined a perpetual pavement as “an asphalt pavement designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction, and needing only periodic surface renewal in response to distresses confined to the top of the pavement.”
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Research and development in the structural design of hot mix asphalt (HMA) pavements over the past fifty years has focused on a shift from empirical design equations to a more powerful and adaptive design scheme. Mechanistic-emp...
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Research and development in the structural design of hot mix asphalt (HMA) pavements over the past fifty years has focused on a shift from empirical design equations to a more powerful and adaptive design scheme. Mechanistic-empirical (M-E) design has been developed to utilize the mechanical properties of the pavement structure along with information on traffic, climate, and observed performance, to more accurately model the pavement structure and predict its life. Although M-E design still relies on observed performance and empirical relationships, it is a much more robust system that can easily incorporate new materials, different traffic distributions, and changing conditions. The M-E design process is more accurately described as an analysis procedure which is used in an iterative manner. The procedure is used to determine the appropriate materials and layer thicknesses to provide the structural capacity for the required performance period.
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The objectives of this study were to develop truck factors for pavement design in Alabama and axle load distribution models for mechanistic-empirical pavement design. In addition, the effects of variations in axle load spectra obt...
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The objectives of this study were to develop truck factors for pavement design in Alabama and axle load distribution models for mechanistic-empirical pavement design. In addition, the effects of variations in axle load spectra obtained from different sites on pavement design requirements using both the 1993 AASHTO pavement design guide and a mechanistic-empirical (M-E) design approach were evaluated. Information from thirteen weigh-in-motion WIM sites on rural principal arterials was provided by the Alabama Department of Transportation for this study. Statistical and practical tests were used to determine the daily, monthly, directional, and site variations in truck traffic relating to the development of truck factors. A sensitivity analysis was performed to determine the effect the variation in truck factors would have on the final pavement design thickness. It was determined that using a statewide average truck factor would be sufficient for pavement design of rural principal arterials in Alabama.
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