There’s nothing small about the Nalley Valley Viaduct project. Every aspect of the Interstate 5-Highway 16 project is scaled large, from the tons of dirt that have to be moved, to the spans of concrete to be poured, to the hulking machines and the skill of the workers needed to operate them.

Last week, crews began drilling massive holes for the foundations of the 79 columns that will support the new bridges and offramps. The first two foundations were completed last week. Drilling will continue for several months.

Next week, the big noise will arrive as crews begin pounding more than 100 steel pipes into the ground on the southern side of Highway 16. The pipes will serve as pilings to support temporary detour bridges that will be completed in the fall.

“It’s going to be a heavy metal concert in Tacoma, but not in the Tacoma Dome,” said Jamie Swift, a spokesman for the state Department of Transportation. “It’s going to be loud. People are going to hear it.”

Things have been quieter, if still visual, this week.

John Joslin of DBM Contractors in Federal Way watched carefully as his drilling crew worked a 9-foot-wide auger into the hillside above Nalley Valley. Joslin’s goal was to dig a shaft 77 feet deep.

“It’s a normal job,” said Joslin, who’s driven augers up to 144 feet deep in the past.

The company will drill 84 shafts for the state’s two-year, $120 million remake of the section of highway that passes over Nalley Valley. Work began in January and is to end in 2011.

To drill the holes, the auger’s circular blades, with 6-inch teeth, chew clockwise into the rocky soil. When the towering yellow machine’s two largest blades are full of dirt, drill operator Tom Gallichan lifts the augur free of the hole and moves it to one side. He spins the blades counter-clockwise, sending dirt flying off the blades.

He repeated the process again and again earlier this week.

Gallichan used a computer in the cab of the excavator to keep the auger centered in the hole. Outside, crewman Tony Whitman kept an eye on the auger’s long shaft to make sure it was straight.

Large metal casings were stored nearby before being embedded in the shaft to help shore up the walls.

The drilling crew also will pump a slurrylike substance into the shaft to help seal the shaft walls.

Drilling is slow but steady work, roughly 31/2 feet per hour. Each foot down produces about 51/2 cubic yards of dirt.

Once the hole is dug, a pre-welded tube of reinforced steel called a cage will be lowered by a 230-ton crane. The crane will use its 160-foot boom to deliver the 83,000-pound cage into the hole.

Finally, 165 cubic yards of concrete will be pumped into the shaft. The concrete will form the base for one of the square concrete columns that will support the westbound overpass from Highway 16 to Sprague Avenue.

Some bridge supports require more than one shaft, said Les DuBois, one of two state field engineers overseeing the project. Two drilling machines will each dig two or three shafts per week, he said.

After the drilling, columns will be built on top of the foundations. Once the columns are up, crews will begin building the road deck.

“The project is progressing really well, and drivers are adjusting to the visual distractions,” Swift said. “It’s pretty spectacular, the things you can accomplish when you have the right tools and the right people doing the job.”

Work started in January with the demolition of two of the four Sprague Avenue fly-over ramps.

“That demolition work was a prehistoric scene with machines like dinosaurs chopping away at raw meet,” he said. “That portion of the demolition ended in March.”

Next up is the noise that will start next week and last a couple of months.

Crews will be pile-driving the steel pipes into the ground for the temporary detour bridges for eastbound and westbound traffic on Highway 16. The pile-driving will occur from about 7 a.m. to 3:30 p.m. weekdays.

Traffic will be moved over to the detour bridges in the fall.

The westbound portion of the project will eliminate the Sprague Avenue offramp weave onto and off of Highway 16 and is expected to decrease collisions by about 60 percent, or 16 wrecks per year.

Once the westbound project is done, crews will begin work on the eastbound project, which should be completed by 2013.

Mike Archbold: 253-597-8692

mike.archbold@thenewstribune.com">mike.archbold@thenewstribune.com

Taking measure of Nalley Valley project

40,000: Average daily viaduct traffic in 1973

131,000: Average daily viaduct traffic today

10: Number of bridges

10.4 million: Pounds of steel expected to be used

48,000: Cubic yards of concrete expected to be poured

200: Number of hourly workers on new project

64 feet: Height of current viaduct

94 feet: Height of new viaduct

22.4 million: Capacity, in gallons, of new permanent stormwater retention ponds