Stormwater | Project Profile

Spanning more than 2,000 miles from Utah to Maryland, Interstate 70 is a popular cross-country route for vacationers and truckers alike. The Colorado portion of I-70 winds traffic through the Rocky Mountains and is 450 miles long. At one point, it extends into the mountainside at the Continental Divide via the Eisenhower Memorial Tunnel, which is the highest vehicular tunnel in the world, at an elevation of more than 11,000 feet.

When a failed storm sewer pipe caused a 22-foot-wide sinkhole underneath I-70 near Vail in June 2003, the Colorado Department of Transportation (CDOT) shut down a portion of the highway for 13 days while crews worked around the clock to replace the pipe and restore the roadway. Repairs cost approximately $4 million.

Recognizing that proactive measures were needed to keep the interstate open and avoid another high-price-tag repair project, CDOT began an aggressive plan to evaluate and restore all large storm sewer pipes running under I-70 to prevent a repeat scenario. This evaluation program revealed another sinkhole that was starting to form near the Eisenhower Memorial Tunnel, about 18 miles east of Breckenridge, in an area that sees 28,000 vehicles per day.

The sinkhole was forming because a 170-foot-long, 24-inch-diameter corrugated metal storm culvert had deteriorated from rust. Parts of the bottom of the pipe were missing, and stormwater flows were running beneath the culvert instead of through it in areas. Although the 30-year-old pipe was coated with a galvanized layer, abrasive mountain runoff containing large amounts of rock and sand had corroded the pipe, causing it to rust prematurely, according to Bill Crawford, project engineer for CDOT.

"Because replacement would have meant shutting down two of the three eastbound lanes, we began exploring different means to correct the problem and decided on cured-in-place pipe technology," Crawford explains.

Breckenridge-based utility contracting firm Western Slope Utilities (WSU), a licensee of Inliner Technologies, was awarded the contract to rehabilitate the pipe. Cured-in-place pipe (CIPP) technology allows for rehabilitation of damaged underground wastewater and storm sewer pipe without excavating. The process reduces noise, traffic disturbance, and road damage, and can be done in less time and money than replacing existing lines. With Inliner's method, a needled polyester felt tube, saturated with resin and coated with a waterproof layer, is inserted into the pipe. Hot water or steam is circulated through the tube, which hardens the resin. This material serves as a barrier between the damaged pipe and the water that flows through it, or as a new standalone pipe.

The project, which was completed in early July 2004, presented WSU with numerous challenges. For example, small boulders and other debris from the mountain runoff had formed a 10-foot-long blockage in the pipe. This debris had to be removed before the CIPP process could begin.

Another challenge was of an environmental nature: Lynx became a state endangered species in 1973, and the area is home to a large population of the cat, which closely resembles a bobcat. The Colorado Department of Natural Resources began a reintroduction program to restore the population in 1998. Because the outlet directed water into Straight Creek, the CDOT environmental division directed WSU to construct a temporary holding pond with an EPDM (ethylene propylene diene terpolymer) geomembrane liner to capture any styrene-laced cure water. WSU could then pump out and haul the water offsite to avoid any environmental contamination.

The upstream end of the 170-foot pipe was located just off the shoulder of the interstate, but the downstream outlet exited halfway down the extremely steep embankment on the other side of the road, dropping nearly 40 feet in elevation. Because of the pipe's steep downgrade, WSU determined that the traditional method of using heated water to cure the resin could result in the liner bursting, because the gravity pull would create an unusually high hydrostatic head pressure during water inversion. "We decided to use an air-pressure inversion and Inliner's patent-pending steam-curing process instead to negate the potentially adverse consequences of water weight," says Dan Cohen, WSU director of operations.

Although steam has been listed in the American Society of Testing and Materials standards since the mid-1980s, its use has been limited because of insufficient knowledge about the process. "With styrenated-based resins, if the temperature rises too high, too quickly, as is possible with steam, the styrene can literally boil," explains Ed Kampbell, Inliner's vice president and general manager. "This would create voids in the CIPP wall structure, producing an unacceptable finished product." He notes that the company has been able to refine the time and temperature relationship to successfully use steam. "We're pleased that our research and development efforts are paying off for organizations like CDOT," he says. "Steam-curing of CIPP has made the relatively shorter lengths of piping common to culvert installations very cost-effective for this method of rehabilitation. It allows us to work with a minimum amount of water, which is not usually found in abundance alongside the highways."

There was also little wastewater byproduct created by the steam process, significantly decreasing the environmental risk and the need for a containment pond, adds Cohen. WSU still built the temporary pond as a safety precaution, but it was not used.

Installation of the cured-in-place pipe took a mere 45 minutes, and the new culvert was completely cured and returned to service in three hours. The entire project, including the installation of a new inlet structure, was completed in one week with virtually no disruption to interstate traffic or environmental damage.

"This was our first experience, not only with cured-in-place pipe, but any trenchless method," Crawford says. "We were really pleased with the outcome. Now we're planning more, including sliplining, shotcrete, and more CIPP projects."

SW January/February 2005

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