Spring 2009 Issue - Special Report
Alaskan Way Viaduct
Posted: April 20, 2009
Boring Technology Is Anything But
A tale of unobtainium and the obtainable solution for the viaduct.
by Jack Mayne
The earth has stopped turning so microwaves are about to cook the world like an apple in a flame. NASA turns to a smart, sexy space shuttle pilot with a gorgeous, toothy smile, Air Force Maj. Rebecca Childs, and asks her to bore a tunnel to the center of the earth and drop off a load of hydrogen bombs that will be detonated to get billions of tons of liquid metal moving again, so the world will resume its spin.
The dashing heroine, “Beck” is given command of a sleek, spaceship-like experimental tunneling machine powered by a new fuel, “unobtainium.” Then, with the help of a hunky male college professor, and against all odds, Beck bores down with great determination and speed, driving her snazzy tunnel machine to the very bowels of the earth where she drops off the hydrogen bombs, narrowly escapes the resulting implosion, and returns to the surface of the earth – at the bottom of the sea – where she and the professor await rescue while realizing they just might be falling in love as the earth, thank goodness, resumes its interrupted spin.
In the 2003 movie The Core, Major Beck was played by Bellingham’s own Hillary Swank, a two-time Academy Award winner who received nothing but awful reviews and a few million dollars for the picture, a box office stinker that sunk from view almost faster than Major Beck’s fantastic tunneling machine.
Unfortunately or not, Beck and unobtainium are not available to provide the so-far unobtainable solution to the dilemma of how to replace the Alaskan Way Viaduct. Meanwhile, however, the Governor, the Mayor, and the King County Executive have decided to use a deep bore tunnel to replace the viaduct and reallife boring technology is anything but.
A machine that would build a tunnel under Seattle’s downtown would not look anything like the sleek, sophisticated vehicle in The Core.
A real tunnel-boring machine looks more like a pile of pipes, tanks, wires, electric motors, cages, and miscellaneous industrial flotsam piled on railway cars. Instead of a roaring, grinding noise, the machine sounds rather quiet underground, and what you hear are the sounds of water, earth, and sand slooshing through pipes and the noise of air ventilators and humming motors.
The future Alaskan Way tunnel will be dug with a special machine designed for the specific soil conditions under downtown Seattle. It will reach depths of 200 or more feet along a route that will extend from a portal near Safeco Field and move north, ending up somewhere in the Lake Union area between the Battery Street Tunnel and Mercer Street.
Not much is known about the project beyond that because only about one percent of the required engineering has been performed. Operational details and challenges will be fleshed out over the next year or so along with lots of design work to figure out the locations of portals where the tunnel will be integrated with surface streets.
Compared to the surface issues, tunneling could prove to be the easy part of the multi-billion dollar project.
In spite of predictable concerns about their safety and reliability, scores of tunnels are already in service or are now being built around the world. The use of laser-guided tunnel boring has become the standard technique, because it gets people, vehicles, and commodities from one location to another without despoiling the surface landscape.
The Swiss are now building the world’s longest tunnel. Thirtyfive miles long, it will create a new direct rail link from Zurich to Milan, Italy. The tunnel will enable the rail line to operate far beneath the Alps at a constant altitude of 1,650 feet the entire way, permitting trains to move between the two cities in two and a half hours instead of the four hours now required to deal with steep grades. The trains will travel at speeds up to 149 miles per hour.
A 3.3 mile tunnel linking the airport in Brisbane, Australia, to the city center will permit congestion-free vehicle flow, bypassing 16 traffic lights. The Queensland state government says the $3.4 billion (Australian) project is under way and on budget. It is due for completion in 2012.
Today the biggest tunnels in the world are currently being bored under the Yangtze River in Shanghai, China, where two tunnels will link Shanghai with Chongming Island. Each tunnel is 51 feet in diameter. The entire project is to be opened next year, a year ahead of schedule.
It is expected that the Seattle tunnel would be dug by a machine 54 feet in diameter.
While there’s no question it will be the state’s highest-profile tunnel project, it won’t really be a new concept because tunnels are a part of the history of Seattle, starting with the Lake Union wastewater tunnel that was hand-dug and completed in 1893. That brick-lined tunnel, still in service today, carries wastewater from the south Lake Union area to the Elliott Bay sewer interceptor.
Then there’s the Stevens Pass Railroad Tunnel, opened in December 1900. That project was an amazing success for its time, as recounted in this passage from the 1935 memoir of John Stevens, for whom the pass was named.
Stevens wrote: “That tunnel was 2 ½ miles in length. The headings met almost exactly at equal distance from the portals with remarkable results. Error: alignment, ¼ inch; grade ½ inch, distance [outside measurement carried over two high mountains] 1 ½ inch. I know of no other case under similar circumstances where this record has ever been equaled.”
Back to the future, in early March digging began for the $1.9 billion phase of a tunnel that will extend light rail from downtown to the University of Washington. Sound Transit reports that this University Link, a 3.15 mile light rail extension, will run in twinbored tunnels from downtown to the university, with stations at Capitol Hill and on the UW campus near Husky Stadium.
The University Link will serve the three largest urban centers in the State of Washington – downtown Seattle, Capitol Hill, and the University District. By 2030, the University Link line alone is projected to add 70,000 boardings a day to the light rail system.
Sound Transit says the underground University Link extension will generate or retain about 2,900 direct construction jobs and provide seven-minute rides between downtown and the university.
The project is on budget, says Sound Transit. Washington Senator Patty Murray, chair of the Senate Transportation Appropriations Committee, worked with the Federal Transit Administration and Sound Transit to secure $813 million in federal funds for the $1.9 billion project.
Three boring machines will be used, two from Husky Stadium heading toward Capitol Hill, and one from Capitol Hill. The project is slated to be completed in 2015.
To date Sound Transit has not opened the larger University Link contracts – but the early ones have been below initial projections. The largest one – to prepare areas adjacent to I-5 for the tunnel machines – came in about 34% below engineers’ estimates.
Another major local project offered us the chance to actually see a tunnel being bored. This is the $1.8 billion, 13 mile long Brightwater sewer tunnel now under way in north King County. One section of the sewer tunnel is 17.5 feet wide, while the width of another section is 19.5 feet.
Unlike Major Beck and her fantastic tunneling machine, the Brightwater machines are not sleek and sexy, but the results usually are.
The two machines on this part of the project were made by Herrenknecht AG, a company based in Schwanau, Germany. These are described as Mixshield machines, and were shipped in parts to Brightwater, where they were assembled.
Each machine is shaped like an immense tin can, with a huge, rotating cutting head that is the size of the tunnel to be built at one end, but open at the far end for disposal of the excavated materials. The heads were specifically engineered for the soil and ground conditions at the boring site. Each head contains a series of round cutting discs. As they are relentlessly ground down by the drilling, they are replaced. Some of the cutting discs used at Brightwater were manufactured in Kent by the 50-year-old Robbins Company.
The massive cutting head face that holds the discs also has openings through which dislodged dirt, sand, and gravel will be drawn, to be mixed with a liquid (often a bentonite slurry) so the mixture can be piped to a separation plant outside the tunnel where the bentonite, a liquid suspension agent, is cleaned and returned to the tunneling machine for reuse.
The sand, gravel, and other materials are separated at the same staging area and disposed of according to regulations.
Both the face of the machine and the ground through which it moves are kept under high pressure to keep the material from collapsing or the tunnel from falling apart. For repairs to the interior of the machine, there are compressed-air locks so that workers can service the cutting head or replace discs or cutterhead parts worn down as they grind rocks or by the abrasiveness of soil and sand.
Everything from the cutting head at the front end to an erector for the new tunnel walls is located inside a protective steel shield, much like a tin can that can make its own concrete walls as it moves forward.
The machines designed for Brightwater will not be used anywhere else, although some parts may get reused for other machines and purposes.
So, that’s the machine. Here is how the boring process works:
The entire machine is encased in a shield, like a tin can, which slides along the bottom of the unlined tunnel. At the trailing edge of the shield, rail tracks are installed – behind the machine itself, to permit equipment and supplies to follow the machine, much like rail cars behind an engine.
A suspension medium is pumped into a sealed and pressured chamber behind the cutting wheels to help liquefy the bored material so it can be pumped away to the surface. Meanwhile, some of this suspension material is also forced under pressure to the forward side of the machine, ahead of the cutting wheels, to help support the ground in front of and around the cutter head. It basically makes a place to move forward by excavating the diameter of the tunnel itself.
Inside the boring machine, a separate process meanwhile erects a set of five semi-round steel-reinforced tunnel wall segments, each five feet from side to side. When five of these are bolted and sealed together, the set creates a new segment of the round tunnel wall.
The entire boring machine is moved forward by a series of thruster cylinders that extend backward from the main boring unit and press against the edges of the installed tunnel wall. These cylinders push the cutting head into the soil to be bored. When the cylinders reach their five-foot extension length, a new five-foot section of the tunnel wall is lifted piece by piece into place, bolted together, and the cylinders are retracted for the next push.
At the same time the rails are extended. Below the machine is a set of wheels that can be retracted as the cutting head moves forward; when it does the next set of rails is installed in the new area of the tunnel floor.
Both the rails and tunnel wall segments are brought in and staged on cars behind the boring machine. The startling thing is that, for the entire unit, the operation requires only a cab operator and a few men who monitor operations and handle special tasks. Everything else is automated.
As for what goes on underground, regulations apply. Just as with air rights, property owners of the surface land have belowground ownership rights. For example, if a machine passes under a farmer’s field in north King County, or a small farm or large home lot, the owner must agree on a cost for boring under the property. Since such subterranean acquisitions are rarely contested, tunnels move quickly once they are under way.
When a tunnel is built in Seattle, each above ground property owner must be dealt with. For that reason, current
thought is that the tunnel will follow a path through City of Seattle–owned property, such as under Second Avenue or other city rights-of-way.
After engineers select and design the boring route, every aspect of the entire boring process will be driven by a computer program. Unlike the movies, you won’t see a comfy cockpit with steering wheels or throttles for comely drivers. Instead, the cab where the tunneling process is controlled has just an array of start switches, an emergency off switch, and several computer monitors.
A laser-aided survey program keeps the machine boring on the proper course, and at the proper depth. All of that is decided by engineering studies of the soil conditions, the amount of water in the soil, and special considerations for aquifers, rivers, and creeks. Changes are made only as necessary. With problems minimized, the advance rate for the tunnel is estimated at from 360 to 550 feet per week, depending on hours worked and the lack of major problems.
That does not mean that highly trained and skilled operators are not necessary. They are definitely present in the control center and, like airplane pilots, use the autopilot when possible, but monitor closely to detect any deviations. These operators are the tunnel-world equals of Captain Chesley Sullenberger, the pilot who brought his automated plane down safely in the Hudson River recently.
Even so, most situations can be designed for in advance, says Jacobs Engineering’s Anthony Pooley, project manager for King County’s Brightwater treatment system project.
In the case of the two tunnels being bored in the current phase of the Brightwater project, one tunnel segment is moving ahead on schedule. The other one is a bit behind because of problems with soil conditions plus some launching conditions that included a tricky curve. The first machine is operating seven days a week, three shifts. The other is active over two shifts with some maintenance time.
Once the tunnel walls are in place, the crew working underground has good light from overhead lighting that is also installed as the tunnel section is built.
One major safety feature that is closely controlled by regulations is fresh air. Found even far from the tunnel entrance, it is delivered by a large, flexible tube suspended from the top of the tunnel. The fresh air is piped in under enough pressure to create a healthy backdraft toward the tunnel opening when released near the boring machine. The rules say that this air must move at a specified rate. There was no hint of bad air or equipment exhaust even deep into the dig area.
The depth of the tunnel also keeps the temperature about even all year no matter what the aboveground temperature is. It appeared to be an even 70 or so degrees during our visit, even though it was much cooler outside.
The Brightwater tunnels will convey treated sewage. When they are completed, all of the pipes, lights, and associated construction equipment will be removed. Completion is expected in 2011.
As with all major construction projects, unexpected problems arise. A sinkhole 15 feet deep, perhaps related to tunneling of the Brightwater project, opened up in a Kenmore driveway on March 8. A boring machine was operating about 150 feet under the area, Judy Cochran said.
Cochran, construction manager for Brightwater, said the boring machine was moving far below the surface in the groundwater layer. A sinkhole can occur if pressure changes, but “it’s pretty rare,” she told the Seattle Times. It’s the first time since the Brightwater project started that a sinkhole has developed, Cochran said.
Crews quickly filled the sinkhole with sand and gravel. There appeared to be no property damage other than the driveway and the sidewalk.
In spite of repeated claims by local critics, the Seattle tunnel is not likely to turn into a “Big Dig” fiasco like in Boston. The Boston project was far larger and far more complex. It combined a huge cut-and-cover ditch with an underground tube, an additional tunnel, and a huge surface-road project that rerouted a 3.5-mile stretch of interstate freeway that once carried nearly 200,000 cars per day through the heart of Boston. By the time it was all over, with debt costs included, it was estimated that the final price tag would reach $22 billion.
The two-mile Seattle tunnel is presently envisioned as a singlebore structure with a radius of 54 feet housing four lanes carrying 80,000 to 85,000 cars each day, with estimated tunnel construction costs of $1.2 to $2.2 billion, with associated costs bringing the total to something more than $4 billion.
Doug MacDonald, the recently retired Secretary of the Washington State Department of Transportation, was the executive director of the Massachusetts Water Resource Authority in the 1990s and supervised some non-vehicle tunnel construction while the Big Dig was underway.
“The Seattle project would have almost no parallel to the Big Dig,” he said recently. “The Seattle project calls for a different kind of tunnel with a different technology and on an entirely different and much more limited scale. Its construction in Seattle would, I hope, avoid the many management problems that plagued the Big Dig. [The state department of transportation’s] record in successful management of large and complex projects is illustrated by the successful Tacoma Narrows Bridge project completed in 2007.”
A reporter visited the completed Boston project recently and was amazed at the major changes made to what was the “Central Artery,” blocking the waterfront from the historic portions of downtown Boston, including Faneuil Hall and the Quincy Market. Now the area is filled with tourists and local residents in a parklike area with new businesses filling what was once an ugly maze of elevated highways and downtrodden businesses.
Not that the Seattle tunnel won’t have its own unique challenges and problems. Major political battles remain before the funding and design package can be nailed down, and a final proposal will require approvals from the Seattle City Council, the King County Council, the Seattle Port Commission, and the Washington State Legislature. There is even a decent chance it might be killed by its detractors before you get a chance to read this.
But as a strategy for minimizing surface disruptions in dense urban landscapes like the one in Seattle, the value of deep bore tunneling is high.
At the end of the journey in The Core, Beck and the hunky college professor who headed the mission lounge together at the bottom of the sea in the cockpit of their tunneling machine awaiting rescue and wondering if anyone will ever know how heroic they and their now dead companions were.
They saved the earth. We seek only to save our city from traffic gridlock and lengthy traffic constrictions while a replacement for the viaduct is being built.
