United States Department of Transportation
i
Evaluation of the base/subgrade soil under repeated loading : phase II, in-box and ALF cyclic plate load tests.
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2012-03-01
[PDF-2.59 MB]
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Alternative Title:In-box and ALF cyclic plate load tests
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Edition:Final report--phase II; Aug. 2005-June 2010.
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Abstract:This research study aims at evaluating the performance of base and subgrade soil in flexible pavements under repeated loading test conditions. For this purpose, an indoor cyclic plate load testing equipment was developed and used to conduct a series of large-scale in-box tests and full-scale field tests on several pavement sections.
The in-box cyclic plate load tests were conducted to evaluate the performance and benefits of geogrid base reinforcement in flexible pavements. A total of 12 tests were performed on unreinforced and geogrid-reinforced pavement sections. The parameters investigated in this study included the aperture shape (geometry) of the geogrid, location of the geogrid within the base layer, and geogrid tensile modulus. The stress distribution and permanent vertical strain in the subgrade, the development of excess pore water pressure in the subgrade, and the strain distribution along the geogrids were also investigated. The test results showed that the inclusion of geogrids can significantly improve the performance of flexible pavements on weak subgrades [California Boring Ratio (CBR) ≤ 1%], and that the traffic benefit ratio (TBR) can be increased up to 15.3 at a rut depth of 0.75 in. (19 mm). Better performance was observed when the geogrid was placed within the upper one third of the base aggregate layer. The inclusion of geogrid helps redistribute the applied surface load to a wider area on top of the subgrade layer, thus reducing the accumulated permanent deformation within the subgrade.
Full-scale field tests were also conducted on several test lane sections built at the Pavement Research Facility (PRF) site using two types of loadings: cyclic plate load test and rolling wheel load test. These sections include blended calcium sulfate (BCS), stabilized BCS, stabilized recycled asphalt pavement (RAP), and stabilized soil as base/subbase materials. The differences in pavement responses of the tested sections to cyclic plate and rolling wheel loads were investigated. The measured rut depth caused by rolling wheel load, in all test sections, were much higher than those measured from the cyclic plate load test. The difference can be as much as 3 to 7 times between these two types of loading. This is mainly due to the effects of principal stress rotation and lateral wander on the permanent deformation of pavements. The field test results also indicate that the cyclic plate load test can be a good performance indicator test for the evaluation and pre-selection of pavement sections for field tests.
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