The Marked Tree Site: Evaluation of Geosynthetic Reinforcements in Flexible Pavements

This document presents findings from a three-year, full-scale, field research project aimed at determining the benefits of using geosynthetic reinforcements to improve the performance of flexible pavements constructed over poor subgrade soils. The test site, known as the Marked Tree site, is an 850-ft (258-m) long segment of low-volume frontage road along Highway 63 in the town of Marked Tree, Arkansas. The site, constructed in 2005, consists of seventeen 50-ft (15.2-m) long flexible pavement test sections with various types of geosynthetic reinforcements (woven and nonwoven geotextiles, and geogrids), which were all positioned at the base-subgrade interface, and two different nominal base course thicknesses [6-in. (15.2-cm) and 10-in. (25.4-cm)]. One section in each nominal base course sector was left unreinforced to allow for monitoring of the relative performance between reinforced and unreinforced sections of like basal thicknesses. The different sections were evaluated in this study using deflection-based, surficial testing conducted between 2008 and 2011, as well as subsurface forensic investigations conducted in October 2010. Signs of serious pavement distress appeared in some of the test sections in the Spring of 2010. Distress surveys revealed that all of the “failed” sections [defined herein as sections with average rut depths > 0.5 in. (1.3 cm)] had nominal base thicknesses of 6-in. (15.2-cm) and were reinforced with various geosynthetics. None of the sections with 10-in. (25.4-cm) nominal base thicknesses had “failed” despite receiving more than twice the number of equivalent single axle loads (ESALs) as the 6-in. (15.2-cm) sections. The impact of base course thickness was easily observed in the deflection-based test results and rutting measurements. However, it was difficult to discern a consistent, clear trend of better pavement performance relative to the various geosynthetic types in each nominal base course thickness. Irrespective of geosynthetic reinforcement type (or lack thereof) all of the sections that “failed” with respect to excessive rutting were the sections with the least combined total pavement thickness (i.e., combined asphalt and base course thickness).

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