Road construction is an ongoing project in most American cities. While the inconvenience of closed lanes and detours creates a headache for commuters, the men and women who design and build our nation's roadways know the importance of deliberation and the careful planning that goes into construction. In other words, do it right the first time or risk having to do it again.

Since September 2001, the New Jersey Department of Transportation (NJDOT) has been working in Woodbridge, NJ, to reconstruct, reconfigure, and widen the roads that make up the interchange where US Route 1 and US Route 9 separate. US Route 1 runs from Maine to Key West, FL, and connects with the historic US Route 9, which travels from Canada to Maryland, entering New Jersey over the George Washington Bridge. From the George Washington Bridge to Woodbridge, the two major roadways are one.

In March 2002, NJDOT became concerned with the subgrade conditions on the Route 9 South portion of the project. Woodbridge is approximately 2 mi. from the New Jersey coastline, and in coastal areas, soils tend to have a higher moisture level than inland areas. Project contractor E.E. Cruz Construction had previously excavated the subgrade, and compaction procedures were underway when the exposed subgrade began to exhibit symptoms of having dangerously high moisture levels. During the operation of the smooth-drum vibratory roller, pumping and rolling of the surface under wheel loads had occurred and ruts had been created in the soft soil after multiple passes of a loaded tandem truck. With signs of structural breakdown occurring so soon in the construction process, there was no possible way that the condition surrounding this roadway would provide for safe driving in the years to come.

Gene Raisley, P.E., resident engineer for NJDOT, called Bill Ragen of Ragen Associates, specialists in geotextile materials and applications, to appraise the situation and offer solutions. The usual DOT repair method of undercutting and replacing the subgrade with stone was extremely expensive, and Raisley wanted to review his options before making a decision. After careful consideration of the project and its problems, Ragen recommended the usage of SI Geosolutions's Geotex 4x4 and Geotex 801 from distributor Brent Materials Inc. to prevent the road deterioration that results from excessive moisture. Raisley had used geotextiles on previous projects but always had to incur the cost and time consumption of undercutting as well. "With this project, we didn't have to undercut," Raisley states. "By using a heavier fabric, we were able to place the Geotex directly onto the unstable subgrade."

Subgrade contamination is the leading cause of pavement failure in the construction industry, and highway engineers typically thicken aggregate layers using sacrificial aggregate to offset the expected losses. The latest alternative to the use of superfluous aggregate is the use of geotextile layers integrated with the subgrade and base/sub-base materials. Geotextiles have a variety of applications, which range from reinforcement on weak subgrades to separation on firm foundation soils. With the use of geotextiles, the subgrade level is effectively separated from the aggregate layer, which helps ensure that the individual layers maintain their original strength and structural integrity. The use of two different geotextile layers in the Woodbridge project would not only provide superior drainage and filtration but also would prolong the life of the road, minimize rutting, and contribute to the even distribution of heavy weight placed on the road's surface.

At Ragen's recommendation, NJDOT made plans to roll out a layer of Geotex 4x4, a high-strength woven geotextile, over the subgrade layer, separating the subgrade from the layer of sand. "I felt that Geotex 4x4 would be strong enough to survive the installation," Ragen recalls. This heavy-duty geotextile is made up of dense monofilament and fibrillated yarns that are woven together to form a unique twill pattern. Geotex 4x4 is ideal for the construction of embankments over soft soils, steepened slopes, and modular-block and wrapped-face retaining walls. It is resistant to ultraviolet degradation and to the biological and chemical environments that are normally found in soil. Woven geotextiles also help ensure that aggregate layers maintain their original design thickness so the strength and durability of the road isn't compromised.

After the placement of the required sub-base material, the second geotextile, Geotex 801, a nonwoven roadway separation/subsurface drainage geotextile, was placed over the layer of sand and under the dense graded aggregate (DGA). This tactic prevents intrusion of the subgrade into aggregate and improves the subsurface drainage of roadways. "Because they were putting two different materials down, the sand and DGA, I felt that we needed a separator between the two," Ragen relates. "The plans called for only an 8-inch layer underneath, and I wanted to have just a little more strength in the material to help the whole system survive, which the Geotex layers provided successfully."

Geotex 801 is a polypropylene, staple-fiber, needlepunched geotextile. The fibers of Geotex 801 form a stable network that retains dimensional stability. Similar to Geotex 4x4, Geotex 801 resists ultraviolet breakdown and biological and chemical contamination, and both geotextiles meet or exceed the American Association of State Highway and Transportation Officials's (AASHTO) M288-00 guidelines.

Construction to repair the site began in mid-April, and Ragen prepared installation instructions with help from SI Geosolutions. The construction team used a smooth-drum static roller to smooth and compact the subgrade without disturbing the water beneath. "Vibratory rollers tend to liquefy the soil underneath the fabric, and it makes it very difficult to stabilize the project," explains Ragen. Geotex has equal strength, whether rolled parallel or perpendicular to machine direction, so NJDOT decided to roll the Geotex 4x4 parallel to machine direction to minimize overlap, keeping in mind that AASHTO recommends a 1.0-m minimum overlap length. An 8-in. layer of sand was placed to serve as a drainage layer. The workers were careful to keep heavy machinery off the roadway until the DGA layer was placed. If any rutting occurred, they filled in the ruts with additional sub-base material instead of cutting off the peaks, which allowed them to achieve proper grade. The first portion of this massive project was finished in mid-June.

The remaining portion of Route 9 South is still under construction. Approximately 23,000 yd.² of Geotex 4x4 and 23,000 yd.² of Geotex 801 have been used in this project to date, and Ragen expects that, upon completion, the project will use an additional 23,000 yd.² of each geotextile. The project thus far has been very successful, and everyone seems happy with the results. According to Regan and Raisley, there is discussion within NJDOT about including geotextiles in its standard contracts. "We're in the business of building roads, and there's always the question of what's down there in the subgrade," notes Raisley. "It would behoove NJDOT to provide for geotextiles in its standard contracts so that we will be prepared when projects like this one come up."

The use of geotextiles was so well received that NJDOT elected to use the same construction solution on the bridge approaches for the new bridge to carry US Route 1 North over Route 9 South. The next project immediately north where Routes 1 and 9 cross Route 35 will also incorporate Geotex geotextiles and will replace the first cloverleaf interchange ever built in the United States.

GEC - March/April 2003