Tuesday, October 24, 2017

Piling on the piles at our flagship ferry terminal

By Broch Bender

What does it take to ensure the largest ferry terminal of the largest ferry system in the United States can stand up to a major seismic event?  It takes a great big pile of…piles!

Almost 500 steel, seismic-grade pilings, to be exact. Not a small number, but it’s only a fraction of the 2,000 or so timber beams currently holding up today’s Colman Dock terminal building and much of the existing dock on the Seattle waterfront.

Back in 1936, Puget Sound Navigation Company rebuilt the terminal building in an Art Deco style to match the company’s newest flagship vessel, the Kalakala. At the same time, they restored the dock by replacing the original 1910 wooden pilings with timber piles bathed in creosote to prevent deterioration.

The state’s minimum wage was 25 cents when Colman Dock got its first complete makeover.
The “Welcome Home” sign was added after the end of World War II. Photo courtesy of Paul Dorpat.
The new, Modernist-style Seattle ferry terminal, dedicated on May 18, 1966.
The Seattle waterfront’s busiest bevy of berths underwent another modern upgrade in 1966, however this Mod style terminal building was built atop the same pre-war creosote timber foundation as its predecessor.

The terminal building at Colman Dock underwent a few more upgrades during the 1980s and ‘90s. In 1990, we expanded the concrete trestle dock south of the terminal building where the Bremerton vehicle holding area is today.

But, back to piling on the piles.
How is it possible to replace thousands of timber columns with only 500 steel tubes? You could say we’re doing more with less.

The Seattle Multimodal Terminal at Colman Dock Project replaces the existing timber trestle with a concrete and steel trestle, so that we can continue to provide safe and reliable ferry service to millions of people across the region.
Each massive steel pile is up to 3 feet wide and 150 feet long. That means one steel pile can cover the same amount of ground as three or more old wooden piles.

The first 138 feet of each new hollow steel pile is driven into Elliott Bay by a vibratory hammer. After that, an 11-ton hammer, powered by a 1,000 horsepower motor large enough to run a locomotive, is heaved to the top of a towering crane and sent barreling down on the pile repeatedly until the column is firmly embedded into Elliott Bay.

This massive 11-ton hammer secures the pile in place below the mudline of Elliott Bay.

The hammer is approximately the weight of two adult male orca whales. Speaking of whales, the project has several marine mammal spotters stationed on the ferry, up and down the waterfront and on Bainbridge Island. All pile driving activity temporarily shuts down when a spotter sees a whale or other endangered species making its way toward Colman Dock.

We stop loud pile-driving work when endangered species are nearby.

Recently our Assistant Secretary for Ferries Division Amy Scarton, Governor Jay Inslee, Rep. Judy Clibborn, King County Executive Dow Constantine and Bardow Lewis, Vice Chairman of The Suquamish Tribe, commemorated the start of pile-driving by signing one of the first support columns to be used on the project.

This “special edition” steel pile will be installed later this month alongside 178 other piles that will make up the deck of the south trestle and part of the new terminal building. The deck is formed by filling up the top 12 feet of each embedded steel pile with concrete and connecting them together with pre-cut concrete panels.

Pile-driving activity occurs during daylight hours, Monday through Friday (with occasional weekends) through February 2018. The work is timed to minimize disruption to our underwater neighbors, migrating and spawning salmon.