The Alaskan Way Viaduct replacement tunnel is a bored road tunnel that is under construction in the city of Seattle in the U.S. state of Washington. The 2-mile (3.2 km) tunnel will carry State Route 99 under Downtown Seattle from the SoDo neighborhood to South Lake Union in the north.
Since 2001, the replacement of the Alaskan Way Viaduct has been the source of much political consternation demonstrating the Seattle process. Options for replacing the viaduct, which carries 110,000 vehicles per day, included either replacing it with a cut-and-cover tunnel, replacing it with another elevated highway, or eliminating it while modifying other surface streets and public transportation. The current plan emerged in 2009 when government officials agreed to a deep-bore tunnel.
Boring of the tunnel with the world's largest-diameter tunnel-boring machine (TBM) "Bertha" began on July 30, 2013.
The project, which was originally scheduled for completion in December 2015, was halted on December 6, 2013 after an unknown stoppage approximately 1,083 feet (330 m) into the planned 9,270-foot-long (2,830 m) route. Investigations a month later revealed that the machine had damaged several of its cutting blades after encountering a steel pipe that was used to measure groundwater in 2002 around the Alaskan Way Viaduct. Over the next two years, a recovery pit was dug from the surface in order to access and lift the machine's cutterhead for repair and partial replacement. Bertha resumed tunnel boring on December 22, 2015. As of July 2016, WSDOT estimated that the tunnel would be completed and open to traffic in early 2019. On January 18, 2016, Governor Inslee stopped tunneling due to a sinkhole above Bertha near the launch pit. Tunneling resumed on February 23, 2016 and broke through to the exit pit on April 4, 2017.
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Planning history
Alaskan Way Viaduct issues
The Alaskan Way Viaduct, completed on April 4, 1953, is a double-decked elevated section of State Route 99 (SR 99) that runs along the Elliott Bay waterfront in the Industrial District and Downtown of Seattle. It is the smaller of the two major north-south traffic corridors through Seattle (the other being Interstate 5), carrying up to 110,000 vehicles per day. The viaduct runs above the surface street, Alaskan Way, from S. Nevada Street in the south to the entrance of Belltown's Battery Street Tunnel in the north, following previously existing railroad lines.
The 1989 Loma Prieta earthquake destroyed the similarly designed Cypress Street Viaduct in Oakland, California with the loss of 42 lives. The 2001 Nisqually earthquake damaged the viaduct and its supporting Alaskan Way Seawall and required the Washington State Department of Transportation (WSDOT) to invest US$14.5 million in emergency repairs. Experts gave a 1-in-20 chance that the viaduct could be shut down by an earthquake within the following decade. After the Nisqually earthquake, the viaduct has been closed semi-annually for WSDOT to conduct inspections of the structure. Those inspections have discovered continuing settlement damage. In 2005, a group of researchers and faculty from the University of Washington urged political officials to close the viaduct within a two-year timeframe.
Options and politics
Several replacement proposals were developed. Many Seattle leaders, including then-Mayor Greg Nickels and state and city transportation officials, favored building a tunnel. Plans for a six-lane, "cut-and-cover" double-decker tunnel were developed. The tunnel was envisioned to solve not only the viaduct's traffic limitations and safety problems, but also to allow better uses for the waterfront real estate, including parks, housing, and retail developments. While future development of the Alaskan Way real estate corridor may provide tax revenue for the city, many state lawmakers objected to the cost of the proposed six-lane tunnel. One criticism compared the plan to Boston's Big Dig project, which was said to illustrate the schedule and budget challenges of a large cut-and-cover tunnel. Proponents responded that the Seattle proposal was significantly smaller in scale than the Big Dig.
Another proposal aimed to replace the current viaduct with another elevated structure with updated seismic standards. This new viaduct would be larger, 12-foot (3.7 m) wide lanes with new shoulders on both sides, compared to the structure it would replace, which had no shoulders and lanes as narrow as 10 feet (3.0 m) in places. The on and off ramps at the northern and southern portion of the viaduct would remain the same with an additional full intersection at South Atlantic Street and South Royal Brougham Way. The First Street off ramp would be removed. The plan included a complete replacement of the sea wall. It was estimated to cost $2.8 billion and take 10-12 years to construct. Many prominent leaders and organizations opposed the elevated structure and believed this was a unique opportunity to remove the viaduct and connect downtown Seattle to the waterfront. Former Governors Dan Evans and Gary Locke, former U.S. Senator Slade Gorton, and the American Institute of Architects recommended against rebuilding the viaduct.
WSDOT evaluated five proposals in 2003-2004 and decided that the six-lane cut-and-cover tunnel was the preferred alternative. Rebuilding the viaduct was retained as a backup plan.
However, due to the costs and scope of the project, other options were still being discussed in the local media. A proposal to remove the viaduct and replace it with surface street and transit improvements was backed by former King County Executive Ron Sims, the People's Waterfront Coalition, and the Congress for the New Urbanism. Proponents of this plan offered examples of successes in removing highways in other cities. They envisioned the waterfront becoming a pedestrian-friendly neighborhood with a mix of commercial, retail, and public park spaces. Traffic needs would be addressed through modifications to existing streets, I-5, and public transit; they argued that these modifications would be desirable in any event. Proponents further argued that this plan had the potential to improve the tourist economy, create jobs, and encourage a denser and more residential downtown through the offering of a generous waterfront park. The total cost of removal of the viaduct, repairing the seawall, and improvements to I-5 and existing streets was unofficially estimated to be $1.6 billion. In 2006, Seattle City Council member Peter Steinbrueck noted, "While the mayor's first choice is the tunnel, he supports the City Council's resolution that designates a surface and transit alternative as a backup."
In response to concerns about the cost of the originally proposed tunnel construction, the city council created a scaled-down, four-lane hybrid tunnel option. This would have combined the smaller tunnel with surface transit improvements to address traffic needs. The tunnel's 14-foot (4.3 m) shoulders would be used as an extra travel lane each way during periods of high demand. Transit service would be increased during peak commuter periods. Cars entering and exiting from Elliott and Western Avenues would each have a dedicated lane. Third Avenue would become a permanent transit corridor. The cost estimate for the four-lane tunnel was $3.4 billion. On February 13, 2007, Governor Christine Gregoire rejected the tunnel hybrid option, saying that a WSDOT review showed the tunnel proposal "does not meet state and federal safety standards." Of particular concern was that the use of shoulders as traffic lanes during peak traffic times would leave no additional lanes for emergency access. However, several of the viaduct "stakeholders committee" brought on board to advise the city indicated that the tunnel option should remain on the table.
State and city officials deadlocked in late 2006 over whether to build an elevated structure (the state's preference) or a hybrid tunnel (the city's preference). Governor Gregoire stated "no action" was not an option for the viaduct. The state government called for an advisory ballot on March 13, 2007, for Seattle residents, which was supported by the city council. The advisory ballot allowed Seattleites to vote on whether they supported a surface-tunnel hybrid and whether they supported an elevated structure. Voters rejected both options, with the surface-tunnel hybrid getting only 30% support and the elevated structure only 43%.
In 2011, Seattleites were asked to vote on the deep bore tunnel option and approved it with 60% in favor.
Bored tunnel selection
In January 2008, as debate on its replacement continued, Governor Gregoire announced that the State of Washington would take down the viaduct in 2012. On January 12, 2009, the state of Washington, King County, the city of Seattle, and the Port of Seattle revealed that they had agreed to replace the viaduct with a bored underground tunnel. On March 4, 2009, the state senate passed a bill endorsing the tunnel option. On May 12, 2009, Governor Gregoire signed Senate Bill 5768, authorizing $2.8 billion in state funds for a possible deep-bore tunnel. Controversy surrounds the tunnel project however, as it was never approved in any general election or referendum, is the subject of multiple lawsuits, was selected before legally required environmental impact studies on both the state and federal level were completed, and is designed in legislation to make Seattle-area taxpayers pay for any cost overruns, which is not the norm for state-level projects, which generally have their costs distributed evenly among all state residents.
Disparate factions, ranging from some environmentalists to some industrialists, criticized the tunnel decision. A business owner argued that the restrictions on hazardous cargo through the tunnel would restrict movement of freight through downtown, though hazardous cargo is already prohibited from the Battery Street Tunnel and the viaduct at peak hours. Similarly, another argued that surface traffic would increase, which would cause further problems to downtown freight transport. A chairman of a local Sierra Club chapter argued that the large investment in automobile transport did not take into account global warming concerns.
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Design, construction, and funding
The approved design is a four-lane, 2-mile (3.2 km) long bored underground tunnel. The tunnel will have a south portal in SoDo, near CenturyLink Field, and a north portal in South Lake Union, east of Seattle Center. The route goes beneath Pioneer Square, the central business district of Downtown, and Belltown.
The project is estimated to cost US$4.25 billion, with $2.8 billion coming from the state and federal governments to cover the tunnel boring and a new interchange in SoDo. The replacement project also includes the following projects and funding sources:
- The city of Seattle will fund surface street improvements, utility relocation, and repairs to the Alaskan Way Seawall, which was also damaged in the 2001 Nisqually earthquake.
- Since the proposed tunnel will contain two lanes in each direction as opposed to the viaduct's three, and no Western Avenue exit to serve the Belltown, Interbay, Magnolia, and Ballard areas, King County will fund transit improvements to offset the loss.
- The Port of Seattle is considering funding part of the project in SoDo.
- $200 million will be collected from tolls at rates set by the Washington State Transportation Commission with input from the Advisory Committee on Tolling and Traffic Management.
WSDOT began part of the larger project in 2008, while the replacement debate was still on-going, by repairing some of the viaduct columns.
The $80 million tunnel boring machine (TBM) Bertha was created for this project by Hitachi Zosen Corporation near Osaka, Japan. The 326 ft (99 m), 6,700-short-ton (6,100 t) TBM was disassembled into 40 pieces and shipped to Seattle where it was reassembled in the launch pit near the south end of the future tunnel. From there, the record-breaking 57.5-foot (17.5 m) diameter borer moves in 6.5 ft (2.0 m) increments toward the north end.
WSDOT nicknamed the TBM "Bertha" after Seattle's first female mayor, Bertha Knight Landes. This name was chosen from names submitted by kindergarten through 12th grade students for a naming competition.
The initial phase of demolition and removal of the viaduct began on October 21, 2011. Only a southern portion of the viaduct was removed at that time; the viaduct along the central waterfront will remain open for traffic until the tunnel is complete.
Boring began on July 30, 2013, and at the time was expected to be completed in 14 months. After three weeks of drilling, the project was estimated to be two weeks behind schedule; problems with fiberglass near the front of the drill and a labor dispute with a local longshoreman's union were blamed. Boring was again delayed in December when Bertha struck a steel pipe, installed as a well casing for an exploratory well drilled as part of the planning phases of the project. This delay lasted for more than two years as the workers had to dig a 120-foot (37 m) vertical shaft down to Bertha's cutting head to repair it. Settling was discovered in Pioneer Square that may be related to this additional excavation.
WSDOT plans to fill in the Battery Street Tunnel after the replacement tunnel is open to traffic, because the 1952 cut-and-cover tunnel does not meet modern safety standards, is expensive to maintain, and will be made redundant by the Alaskan Way tunnel. Dirt produced by tunnel construction will be sent to fill a CalPortland quarry in nearby Port Ludlow, Washington.
Tunnel boring had resumed on December 22, 2015. The tunnel boring was halted 23 days later on January 14, 2016, after a 30-foot-wide (9.1 m) sinkhole developed on the ground in front of the machine, causing Governor Jay Inslee to halt drilling until the contractors can perform a root cause analysis to show that the machine can be run safely. Even though contractors filled the hole with 250 cubic yards (190 m3) of material, the ground above the tunnel-boring machine is continuing to sink, according to the Washington State Department of Transportation. The tunneling restriction was lifted on February 23, 2016, and tunneling resumed that day. Bertha passed under the Alaskan Way Viaduct in early May, closing the roadway for 11 days as the machine had 15 feet (4.6 m) of vertical clearance under the structure's pilings. As of April 4, 2017, the tunnel boring machine broke through to the recovery pit on the north end of the tunnel, completing the excavation process and will be removed from the site as the next step, taking four to five months.
As of July 2016, Seattle Tunnel Partners expects to have the tunnel completed and open to traffic in early 2019. An estimated $223 million in cost overruns were reported as a result of the two-year stoppage.
Source of the article : Wikipedia
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