Equipping a once-fatal highway to deliver solid future performance

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Courtesy of Thrace Plastics Pack S.A.

Background

Stretching 1189 miles along the southeastern coast from Virginia to Florida, the Ocean Highway (US 17) mixes magnifi cent scenery with unpredictable driving conditions. In 2005, the South Carolina Department of Transportation (SCDOT) called its 211-mile stretch of US 17 one of the deadliest roads in the nation; and between 1997 and 2005, the highway experienced nearly 1,000 recorded automobile crashes. Due to its heavy use, most of the South Carolina section of US 17 had been improved and expanded into multiple lanes. However, by 2004, six miles remained with only two lanes, creating hazardous conditions for the motorists who traveled there. With public and political pressure mounting, this section became top priority for an upgrade, and a transportation sales tax was created to fund the project.

Project Challenge

Over two years, the fatally narrow stretch of highway underwent expansion from two to four lanes, at an estimated cost of $80 million.* Its high profile nature demanded that the project feature quality construction that would sustain heavy use with little to no premature maintenance. Since most pavements fail prematurely due to base contamination and the subsequent loss of strength and drainability, the designers and engineers would need to address this challenge head on. Additionally, protecting the environment and minimizing the impact on traffic were major concerns during construction.

Project Design

For the upgraded section of US 17, two lanes of traffi c in each direction would be separated by a 100-foot-wide median. Unfortunately, the area was prone to weak, silty subgrade and the potential for high precipitation and groundwater levels. Designers solved this challenge by specifying a separation/stabilization geotextile beneath the road. Such a geotextile provides a remarkable dual benefit, both lowering initial project costs and reducing the need for future road maintenance.

Though a geogrid (an open mesh material) was originally considered for this project, the positive separation, greater strength and signifi cant cost savings of a geotextile made it far more attractive. Designers for the US 17 project specifi ed an AASHTO M-288-99 Class 1 woven geotextile, which would feature the strength, elongation and permittivity that would best suit the site conditions imposed by the subgrade and aggregate base. The Class 1 specifi cation also ensured that the geotextile would meet survivability criteria, including resistance to puncture damage and UV resistance, before it was covered with the aggregate base material.

The selected geotextile, Thrace-LINQ GTF300, is a heavy-duty, high-quality woven polypropelyne geotextile. It was placed on the prepared subgrade, and then covered with road base aggregate. Since GTF300 maintains the full thickness of the base aggregate, no additional, sacrifi cial aggregate is needed. In addition, the geotextile’s stabilization increases the effective strength of the base and subgrade. As a result, the structural section of the road can be signifi cantly reduced to save on material costs. Additional savings are achieved as future maintenance needs are drastically reduced. Geotextiles like GTF300 provide a host of benefi ts, with a typical cost of no more than one to two inches of aggregate. It is a smart investment for any road project.

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