Project
Central Texas Turnpike, Texas State Highway 130

Joint venture group
Lone Star Infrastructure

Product application
A flexible growth medium and turf reinforcement mat system provide critical slope revegetation in difficult conditions along a new highway.

Erosion control efforts overcome drought, variable soils, and damaging rainstorms.

"Everything’s bigger in Texas," is a popular phrase that can even apply to Texas’ erosion control challenges. Officials involved in a Texas highway construction project quickly discovered the phrase aptly described troublesome, highly erosive slope grades and ditches of a high-profile, billion-dollar road construction project. Two segments of a 90-mile stretch of the privately financed and constructed Central Texas Turnpike Project (CTTP) were proving extremely difficult to establish vegetation. The project faced drought conditions, poor soils, and sporadic, damaging rainstorms.

Despite drought conditions, vegetation was quickly established on the first two segments of SH 130 using Profile Products’ Flexterra Flexible Growth Medium on slopes and GreenArmor Turf Reinforcement Mat system in ditches.

As Central Texas’ population has increased, so has its traffic congestion. To remedy this, the Texas Department of Transportation and the Texas Turnpike Authority developed the CTTP, ranked as one of the nation’s largest construction projects. The largest component of the CTTP is a 90-mile stretch of Texas State Highway 130 (SH 130). When completed (expected completion date of December 2007), SH 130 will extend from north of Georgetown, Texas, which is east of metropolitan Austin, to I-10 near Seguin, Texas. This stretch represents an investment of $1.3 billion dollars. According to its project website (www.sh130.com), SH 130 is the state’s first highway to be developed under a comprehensive development agreement, allowing property acquisition, design, and construction to be undertaken simultaneously.

The primary contractor for this project is Lone Star Infrastructure (LSI); organized as a joint venture between Fluor Corporation, Balfour Beatty Construction, and T.J. Lambrecht Co., it includes seven teams of consulting engineers and contractors (see "SH 130 design team").

Revegetation problems
By late summer of 2006, slope revegetation on the first two segments of SH 130 was far behind schedule. The area had been in a drought for several months and aggressive measures were needed to establish sufficient cover to ensure that the two segments—totaling about 20 miles—could be opened for traffic before year’s end. One reason for the delay was the variety of soil conditions on the slopes, which ranged from rocks and shale to sandy clay. This made it difficult and time consuming for the reclamation contractors, ABC Erosion Control and C-3 Environmental Services, to achieve the optimum grade conditions needed to use rolled blanket-type materials for growth establishment. In addition, the design of SH 130, with converging slopes and multi-lane pavement on banked curves, created many areas where heavy runoff could concentrate. While geosynthetic mats were being used in these areas of high erosion potential, growth establishment here, as it was on the slopes, was substantially behind schedule.

Slope revegetation on the first two segments of SH 130 was behind schedule because the area had been in a drought for several months. Aggressive measures were needed to establish sufficient cover before opening the highway.

Geo-Solutions, Inc., located in Austin, Texas, proposed to LSI that it test Profile Products’ Flexterra Flexible Growth Medium (FGM) on the first two segments of SH 130. Geo-Solutions’ experience indicated that the FGM could establish growth under the existing challenge of drought conditions while protecting against the heavy rain storms common to the area. According to the company, with greater than 99 percent effectiveness in controlling soil loss, the FGM has been proven to outperform rolled erosion control blanket and bonded fiber matrix products. Flexterra does not require cure time, provides immediate protection against erosion upon application, and absorbs and holds 15 times its weight in water, delivering more moisture to the seedbed for faster vegetation establishment.

LSI accepted the proposal and two tests were conducted in August 2006. LSI also brought in its project specialist, Mike Bagby, to supervise the revegetation.

"I’d been involved in numerous projects where curled fiber blankets were used," Bagby said. "They work okay if you can get a perfect grade. But that wasn’t easy to do on this project. However, not having a perfect grade didn’t seem to matter with the Flexterra. The FGM was sprayed on a Thursday, and we had millet coming up the following Monday."

Dan Corrigan, who managed the hydro-application project for C-3 Environmental Services, concurred: "The demonstration test was on a steep (2H:1V) grade. We shot about 5,000 square feet with the Flexterra, and we had vegetation within three days. I think the speed is due to the fact that the FGM bonds to the ground. You don’t get that kind of soil contact with blankets, which results in open spaces where rills can easily form."

With the success of the demonstration, LSI decided to put the FGM to work on the first two SH 130 segments. "We couldn’t justify using Flexterra on all the slopes," Bagby said, "so we were selective in picking the difficult areas where we knew it would be hard to hold the topsoil and establish growth. In addition, we wanted to concentrate on areas where aesthetics would be more important, such as around toll plazas. So we had to move around a lot and wound up covering a patchwork of different areas that totaled about 80 acres."

Geo-Solutions also recommended Profile’s GreenArmor Turf Reinforcement Mat (TRM) system for speedy revegetation in ditch areas. The GreenArmor system combines Enkamat TRM with Flexterra to create an economical system that, according to Profile, protects against elevated levels of hydraulic lift and shear forces on slopes and in channels while encouraging fast turf establishment and long-term root reinforcement. Enkamat is a 3-D TRM made of polyamide (nylon) filaments thermally fused at their intersections to create a lofty, homogeneous matrix. Because the matrix consists of 95 percent open space, it readily accepts the hydraulically applied FGM infill. As vegetation roots grow, they became entwined within the TRM matrix, creating a stable cover. When fully vegetated, Profile says the system doubles the effectiveness of natural vegetation and can replace hard armor systems such as rock and concrete.

Results
Switching to the FGM and GreenArmor system was a positive factor in vegetating the slopes and ditches along the two SH 130 segments and getting them open on time. Segment Two, between U.S. 79 and U.S. 290, opened Oct. 1, 2006. Segment One, between I-35 and U.S. 79, opened Dec. 10, 2006.

Then the rains came. In late December 2006 and early January 2007 there were several, inch-a-minute cloudbursts, including one in which 4 inches of rain fell in four hours.

"While we definitely got the boost in regrowth we needed, we did have to do some repair after the rains came," said Bagby. "However, I don’t know of anything that could have withstood the amount of rain we had and still be able to establish vegetation. All in all, we were very satisfied."

Sarah Willnerd is a writer with Swanson Russell Associates in Lincoln, Neb. She can be contacted at sarahw@sramarketing.com.

SH 130 design team
In addition to joint-venture partners Fluor Corporation, Balfour Beatty Construction, and T.J. Lambrecht Company, Lone Star Infrastructure (LSI) includes the following teams:

Design

• DMJM+Harris
• S&B Infrastructure, Ltd.
• P.E. Structural Consultants, Inc.
• CTL | Thompson
• Dan Zollinger, Ph.D., associate professor in materials engineering, Texas A&M
• Dallas Little, Ph.D., Snead Chair professor and division head of materials engineering, Texas A&M
• PSI
• UNINTECH Consulting Engineers, Inc.
• Yvonne Newman Engineering, Inc.
• Turner Collie & Braden, Inc.
• Menon Consortium, Inc.

Right of way

• O.R. Colan & Associates
• Macias & Associates

Environmental

• Hicks & Company

Utilities relocation

• TBE Group

Independent quality assurance

• Bridgefarmer & Associates
• OTHON
• Atkins-Benham
• Landtech Consultants
• Raba Kistner Infrastructure, Inc.

Construction

• Austin Bridge & Road

Asset management/maintenance

• VMS