Engineering challenges abundant on freeway job

Nasty dirt dirt so corrosive that it eats just about anything that comes in contact with it drove engineers to distraction as they planned the extension of U.S. 395 south of Reno.

But now a pile of the dirt taller than the Nevada State Capitol will allow construction of the bridge that holds the key to the entire project.

Commuters speeding along U.S. 395 through Pleasant Valley might not see many changes taking place on the freeway extension, but the eight-mile project has been a virtual hive of activity since North Dakota-based Fisher Sand and Gravel began work in January.

Behind rugged hillsides, big bridges and huge retaining walls are being erected. Bulldozers and scrapers scurry to beat winter weather.

Soon the most challenging and controversial piece of the puzzle, the Galena Creek Bridge west of Pleasant Valley, will finally take shape.

Work began in August to fill the creek's narrow canyon with dirt. The complex plan involves casting a mammoth concrete arch 44 feet wide, 400 feet long, 22 feet tall through which the creek will flow during the construction.

It will be topped by a 30-foot vertical retaining wall and then by 120 feet of soil fill a pile of dirt eight feet taller than the state capitol building.

And the whole thing arch, retaining wall and dirt all will be removed once the bridge is complete.

Once the dirt has been raised to the base of the main piers of the bridge, erecting the temporary supports for the 1,725-foot arched-truss bridge should pose few challenges for bridge builder CC Meyers of Sacramento.

CC Meyers crews poured the first 50-foot segment of the arch last week and expect to finish it by Thanksgiving, says Brad Durski, an assistant resident engineer for the Nevada Department of Transportation.

Durski is quick to note that the Galena Creek bridge is but one piece of the $393 million job. Each of the nine structures on the freeway extension required unusual engineering to deal with topography and soils.

A bridge at Galena Forest, for instance, sits on mammoth foot-thick pads because high geothermal activity didn't allow for drilling to support piers.

The second largest structure on the project, the Steamboat Bridge, spans 700 feet. Though the bridge is hidden from traffic on U.S. 395, much of the falsework that will provide temporary support already is in place. Piles 12 feet in diameter are buried 60 feet into the ground and rise 120 feet in the air, waiting to be connected.

Elsewhere, Fisher crews are busy erecting giant earthen retaining walls to carry the roadbed. The first of them, but not largest to be built, already can be seen from U.S. 395.

"I tell my guys every day, if you aren't having fun on this project, you will never have fun," Durski says. "Everything you could ever want to see on a project is happening. Look at all the dirt we have moved, the walls we've built. It is just incredible."

NDOT accepted but didn't formally approve the plan to use fill to create the Galena Creek bridge.

"We have allowed them to move forward with it. We accept it and we approved the drawing, but we don't actually approve the whole process itself. That is too much liability for NDOT to take," Durski says.

The plan took six months of collaboration with NDOT, Fisher and CC Meyers. Fisher's original plan called for an 11-foot culvert.

"The Corps of Engineers and the BLM said an 11-foot culvert wouldn't work," Durski says. "If you get a 100-year event coming down that canyon, it would back up to (Montreaux) and have the potential to wash this whole area out."

The culvert itself is a feat.

The arch, 30 inches thick, sits atop two 17-foot concrete footings that were poured anywhere from five to 20 feet thick. Atop that sits a four-foot tall footing that will carry the arch. The smaller footings required more than 2,000 yards of concrete, while the base required more than 5,000 yards of slurry. More than 1.2 million pounds of rebar were used in the footings.

It will all be removed when the work is done.

Durski says the fill material will be moved in and out via conveyer belt, and the culvert will be sawed into pieces for removal.

The job turned out to be much more expensive than originally drawn up, but Durski says Fisher Sand and Gravel also caught some breaks.

It was able, for instance, to sell as scrap some $5 million in steel for the truss built by Edward Kraemer & Sons Inc., which left the project in 2006 after its executives voiced doubt the Galena Creek bridge could be built safely under the original plans.

Acceptance of the fill plan also meant Fisher shaved 100 working days off the original 1,000 slated for the entire job another major savings.

Fisher, who will use the top of the Galena Creek fill as a roadway to transport more than four million cubic yards of dirt from the north end of the job to the south, is simply happy work finally can begin.

"We can't wait to start filling it up with dirt," he says. "This is a pretty complex change we are asking for, but everyone got on board.

It takes a lot of time and effort with every cooperating to make something like this happen. I am just glad to see it being constructed and us able to go on."

Fisher already has crushed nearly all the aggregate needed for the job. Durski says much of the dirt has proved to been a stew of sand, decomposed granite, and of course, rock.

"Every couple of feet it changes," he says. "The contractor had a hard time determining whether or not he could make material on-site, but Fisher was lucky, unearthing a huge cap of basalt that they will mix for all their concrete needs."

When it's completed, the new road is expected to handle about 75 percent of the 40,000 cars a day that travel U.S. 395 south of Reno.