United States Department of Transportation
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Accelerated Load Testing of Geosynthetic Base Reinforced/Stabilized Unpaved and Pavement Test Sections
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2019-08-01
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Edition:Final Report, Dec 2010 -June 2018
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Abstract:This research study aims at evaluating the benefits of using geosynthetics to reinforce/stabilize base aggregate layer/subgrade in pavements under repeated loading test conditions. For this purpose, a total of six 80-ft long and 13 ft wide full-scale test lane sections were constructed, among which two sections were reinforced by one or two layers of triaxial geogrids, two sections were reinforced by one layer of high strength woven geotextile with different base layer thickness, and the remaining two sections were the control sections. The field test sections were instrumented by a variety of sensors to measure the load- and environment-associated pavement response and performance. Two series of tests, moving wheel load tests and cyclic plate load tests, were conducted to investigate the field performance of geosynthetic reinforced/stabilized paved roads and to identify the differences in pavement response to moving wheel and cyclic plate loads. In addition, six similar test sections were constructed inside a 6.5-ft × 6.5-ft × 5.5-ft test box. The test box sections were also instrumented by a variety of sensors to measure the load-associated pavement response and performance. Laboratory cyclic plate load tests were then conducted. The results of accelerated load testing on the pavement test sections demonstrate the benefits of using geosynthetics in reducing the permanent deformation in the pavement structure. The adjusted traffic benefit ratio (TBRadj) associated with geosynthetic reinforcement can be increased up to 2.12 at a rut depth of 0.75 in. for pavement constructed using 18 in. thick base layer on top of weak subgrade soil using two layers of geogrid reinforcement. The inclusion of geosynthetics results in redistributing the applied load to a wider area, thus reducing the accumulated permanent deformation within the subgrade. The benefit of geosynthetics on reducing the maximum stress on top of subgrade is more appreciable at higher load levels. It was also found that the geosynthetics placed at the base-subgrade interface was able to improve the performance of both subgrade and base layers; by placing an additional layer of geogrid at the upper one-third of the base layer, the performance of the base layer was further enhanced. While geosynthetics showed appreciable benefit on reducing the permanent deformation of the subgrade layer, it showed less effect on the resilient properties of the subgrade layer. Drainage of the base layer has important effect on the performance of pavement structures for both unreinforced and reinforced lane sections. The life-cycle cost analysis (LCCA) demonstrated the cost savings of using geosynthetics in pavement as compared to the unreinforced/untreated sections. However, compared to the 12-in. cement/lime treated subgrade with the cement stabilized base pavement section, the LCCA showed it is more cost effective to use geosynthetics for base thickness less than 12 in. (or < 15 in. of unreinforced aggregate base). The cost benefit becomes close for base thickness > 12 in. between using a single geosynthetic layer and a 12-in. cement/lime treated subgrade with a cement stabilized base. Moreover, the cost benefit of using double geogrid layers exceeds the cost savings of a 12-in. treated subgrade with a cement stabilized base.
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