Test pile-driving began Tuesday at Sacramento's historic railyard as the site's developers prepare for bridge construction.

The sights and sounds were a sample of what's to come in about four months when foundation work starts for bridges on Fifth and Sixth streets.

At that time, the developers at Thomas Enterprises realize some neighbors may be annoyed by the booms of about 400 piles being driven into the earth. But the noise won't be the same to all ears, they said.

"To us, it's the sound of progress," said Leslie Valpey, the project's development coordinator. "And activity at a time when there's not a lot of activity."

That sound also represents the historic Southern Pacific railyards coming to life again after decades of disuse and decay.

Other infrastructure work has already been done elsewhere on the site, where a $6-billion mixed-use district containing a new regional transportation center is expected to be built over the next 20 years. 

Infrastructure work includes the initial grading of Railyards Boulevard and northern portions of Fifth and Sixth streets. Abatement inside the historic Central Shops and building up the elevated 10-acre Vista Park with soil has also begun.

The bridges will be built in the section of the 244-acre site that lies closest to downtown. The two bridges will provide a way for extensions of the two streets to travel over new, relocated tracks and into the heart of the Railyards.

Work crews are using a 120-foot crane to drive six test piles there this week. The piles create the bridges' foundations.

"The most important thing is really these (piles), because that's what's holding the bridge when it goes up," said Elias Rashmawi, director of land redevelopment for the project. "It's the foundation work."

Two types of piles — an H pile and a pipe pile — are being driven into the ground at three locations. Crews drive a 60-foot pile into the ground, weld a second of the same length on to that, and drive the entire pile down 115 to 118 feet, he said.

The piles go through sand, then gravel, then a layer of sand and gravel and silty sand, as well as water, because an aquifer starts 20 feet below the ground, he said.

Readings are taken on resistance, load and stress, to show how much capacity the piles can handle. The tests help the designers and installers determine which type of pile to use and at what depths and where. Pile driving for the bridge is expected to take one to two months.

The bridges will be built over the tracks, and two pedestrian tunnels will be built under the tracks. One tunnel will start at the historic Sacramento Valley Station and the other at Old Sacramento. Bridge construction is expected to be finished by next fall.

Track relocation work, which will be overseen by the city of Sacramento, will be done at the same time, according to Thomas Enterprises Vice President Suheil Totah. New tracks will be laid and trains will begin using those before the old tracks are dismantled.

Fifth and Sixth streets are expected to be completed after that.

Thomas Enterprises is handling all the bridge and road work as part of a partnership with the city. The city won a grant to fund construction of the Sixth Street bridge and the developer was awarded Proposition 1C funding for the Fifth Street bridge, Totah said.

Photos by Kati Garner. Suzanne Hurt is a staff reporter for The Sacramento Press.