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Accelerated characterization of full-scale flexible pavements using a vibroseis.
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  • Edition:
    Final report; 7/1/08-1/31/10.
  • NTL Classification:
    NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance
  • Abstract:
    Geosynthetic basal reinforcement has been used in flexible pavements and unbound roads to limit the occurrence of rutting, fatigue, and environmental-related cracking, and to permit reduction in base course thickness. However, the lack of a representative, cost-efficient test that can be used to evaluate the behavior of full-scale pavement test sections has prevented parametric analyses of variables that may affect the performance of basally-reinforced flexible pavements (base thickness, subgrade and base soil properties, geosynthetic properties, depth of geosynthetic placement, stress state, and load magnitude and frequency). Current accelerated tests involve either small-scale, laboratory cyclic plate load tests, which often have scale effects, or heavy vehicle simulators, which require significant space, high construction costs, and long durations. Accordingly, the research objective of this study was to develop and validate new accelerated testing approaches using a Vibroseis (shaker truck) to characterize large-scale, geosynthetic reinforced pavement models. This report includes a description of the methodology and results from two different types of dynamic tests using a Vibroseis truck as the loading mechanism: (1) relatively small-strain tests (shear strains less than 0.2%) where embedded geophones allowed for measurement of shear and normal strain distribution within the geosynthetic reinforced test sections as a function of depth, and (2) relatively large-strain tests (surface deflections on the order of 1 inch) where significant numbers of ESAL‟s (30,000 plus) were applied to the geosynthetic reinforced test sections while permanent surface deflection basins were monitored with LVDT‟s as a function of number of loading cycles. These two dynamic tests were conducted on large-scale unreinforced, geogrid reinforced, and geotextile reinforced test sections constructed in a 4-ft deep by 12-ft wide by 12-ft long pit at the Engineering Research Center (ERC) of the University of Arkansas. The small-strain tests were performed on test sections constructed completely out of poorly-graded sand. This simple, uniform material was chosen so as to evaluate how geosynthetic reinforcement influenced subsurface strain distribution without interference from other complicating factors that would make relative comparison of strain distribution difficult (i.e. different soil layer interfaces, varying negative pore water pressures in soils with significant fines content, etc.) The large-strain tests were performed on test sections constructed out of 10 inches of Class 7 base course overlying 30-plus inches of poorly-graded sand. Both sets of tests were performed so as to determine the contribution of geosynthetic reinforcement to structural pavement performance (i.e. relative strain distribution and surface deflection only). No attempts were made to evaluate the other potentially beneficial mechanisms of geosynthetic reinforcement. This report is separated into five chapters. Chapter 1 consists of an introduction. Chapter 2 is a literature review related to geosynthetic reinforcement of the base layer in flexible pavements. Specifically, this review will focus on studies involving construction and evaluation of pavement test sections with and without geosynthetic reinforcement. Chapter 3 summarizes the testing approach used to evaluate the impact of geosynthetic reinforcement on the in-situ strain distribution during dynamic surface loading. Chapter 4 presents a description of the accelerated dynamic deflectometer (ADD) testing approach and results from this large-strain surface loading test. Chapter 5 presents conclusions developed from the current research.
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