It wasn't the size of the 11,000 ton asphalt project that made paving the Eisenhower-Johnson Memorial Tunnel difficult. It was the myriad details and obstacles with this unique application that posed the challenges. From the tunnels' low clearance and pavement's specified mix design to the weather and trucking issues, Pavetec Inc., of Silverthorne, CO adapted well to the many twists and turns it faced.
Simply the altitude and ambient conditions of the tunnels, located just outside of Denver, made for difficult paving. Perched at more than 11,000 feet above sea level, the two, 1.7-mile long lanes of the westbound and eastbound bores are the highest vehicular tunnels in the world. "When paving at this height, you have to make sure your equipment is in top operating condition," says Mitch Olson, project coordinator for Pavetec.
Steep seven percent grade approaches and an average snowfall of 312 inches between November and April significantly wreak havoc on the pavement's surface. "When the snow flies in Colorado, the tire chains are put on," says Alan Adams, president of Pavetec. "Abrasion from the chains really affects the service life of the road."
The last complete overlay of the tunnel roads was in 1997, less than 10 years ago. "We design the surface for a 10-year life, but in this environment — heavy truck traffic, weather, salt and chains — we are satisfied with a seven- or eight-year life," explains Ina Zisman, resident engineer for the Colorado Department of Transportation (CDOT).
The tunnel itself forced the contractor to alter typical paving practices. A low, 15-foot clearance and maximum truck height of 13 feet 6 inches to compensate for message boards and signs hanging from the ceiling eliminated the prospect of using end-dump trucks. "We secured live-bottom trucks for this project," says Rusty Evans, transportation manager for Pavetec.
Inside the tunnel, constant temperatures hovering around 50 degrees Fahrenheit contributed to the decision not to use windrow paving. However, the mix design ultimately ruled out this continuous paving process. "The mix we are using is very tender, so we could not windrow the material," says Zisman.
CDOT specified an open-graded Stone Matrix Asphalt (SMA) PG 64-28 mix design with a 3/4-inch (19-mm) top aggregate size for the Eisenhower-Johnson Tunnel project. This coarse aggregate, polymerized mix with high oil content is expected to withstand the abuse of nearly 47,000 vehicles per day during peak season. However, paving with the mix proved to be difficult.
"You cannot handwork this mix," says Adams. "It has to be put down right the first time." An easier-to-handwork "SX" variation of the mix with a more evenly graded aggregate composition was used to pave around drainage openings and other obstacles along the tunnels' walls.
CDOT has stringent specifications for paving with an SMA mix design, calling for areas behind the paver showing signs of flushing to be immediately removed. Paving operations are to cease if segregated areas are discovered until the causes of the problem are discovered and corrected.
Pavetec had absolutely no time to deal with segregation issues. Since asphalt paving completely closed one bore to traffic — which redirected all traffic to the opposite bore, leaving only one lane open in each direction — Pavetec and the project's general contractor, American Civil Constructors of Denver, had limited time to complete the work.
The asphalt and concrete removal, resurfacing, repairs and other associated work for both bores had to be completed within a three-week time period. All lanes, however, had to be reopened to traffic during the weekends. "We chose to do the project in September because it has the lowest traffic counts at 25,000 vehicles per day," says Zisman.