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84-411: [REDACTED] The State Route 99 tunnel , also known as the Alaskan Way Viaduct replacement tunnel , is a bored highway tunnel in the city of Seattle , Washington , United States. The 2-mile (3.2 km), double-decker tunnel carries a section of State Route 99 (SR 99) under Downtown Seattle from SoDo in the south to South Lake Union in the north. Since the 2001 Nisqually earthquake ,

168-516: 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 was closed twice a year for WSDOT to conduct inspections of the structure. Those inspections 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

252-545: 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 m) of material, the ground above the tunnel-boring machine continued to sink, according to the Washington State Department of Transportation. The tunneling restriction

336-591: A block south at South Atlantic Street. The tunnel carries two lanes of southbound traffic on its upper deck and two lanes of northbound traffic on its lower deck, and functions as a complete bypass of Downtown Seattle with no intermediate exits; it has a posted speed limit of 45 miles per hour (72 km/h). The tunnel travels northwesterly under Pioneer Square and Downtown Seattle, generally following 1st Avenue . It reaches its deepest point at Virginia Street, approximately 211 feet (64 m) below street level, and begins its turn north through parts of Belltown and

420-616: A boring diameter of 6.67 m (21.9 ft). The medium was water saturated sandy mudstone, schistose mudstone, highly weathered mudstone as well as alluvium. It achieved a maximum advance rate of more than 345 m (1,132 ft) per month. The world's largest hard rock TBM, known as Martina , was built by Herrenknecht AG . Its excavation diameter was 15.62 m (51.2 ft), total length 130 m (430 ft); excavation area of 192 m (2,070 sq ft), thrust value 39,485 t, total weight 4,500 tons, total installed capacity 18 MW. Its yearly energy consumption

504-497: 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

588-500: A deep-bore tunnel. Construction began in July 2013 using " Bertha ", at the time the world's largest-diameter tunnel boring machine . After several delays, tunnel boring was completed in April 2017, and the tunnel opened to traffic on February 4, 2019. The SR 99 tunnel is a single tube that measures 9,270 feet (2,830 m) long and 52 feet (16 m) wide, carrying a double-decker highway that

672-471: 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

756-457: A leading shield that advances with the cutting head and a trailing shield that acts as a gripper. The two shields can move axially relative to each other (i.e., telescopically) over a limited distance. The gripper shield anchors the TBM so that pressure can be applied to the cutter head while simultaneously the concrete lining is being constructed. In hard rock with minimal ground water, the area around

840-568: A local Sierra Club chapter argued that the large investment in automobile transport did not take into account global warming concerns. The approved design is a four-lane, 2-mile (3.2 km) long bored tunnel. The tunnel has a south portal in SoDo , near Lumen 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

924-435: A plug to form in the screw. The cutter head is filled with pressurised slurry, typically made of bentonite clay that applies hydrostatic pressure to the face. The slurry mixes with the muck before it is pumped to a slurry separation plant, usually outside the tunnel. Slurry separation plants use multi-stage filtration systems that separate spoil from slurry to allow reuse. The degree to which slurry can be 'cleaned' depends on

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1008-593: A possible deep-bore tunnel. 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

1092-480: A rotating drum with metal tines on its outer surface, or a rotating circular plate covered with teeth, or revolving belts covered with metal teeth. However, these TBMs proved expensive, cumbersome, and unable to excavate hard rock; interest in TBMs therefore declined. Nevertheless, TBM development continued in potash and coal mines, where the rock was softer. A TBM with a bore diameter of 14.4 m (47 ft 3 in)

1176-402: A single cylindrical shield after the cutting head. A permanent concrete lining is constructed immediately after the shield, and the TBM pushes off the lining to apply force to the cutter head. Because this pushing cannot be done while a next ring of lining is being constructed, the single-shield TBM operates in alternating cutting and lining modes. Double Shield (or telescopic shield) TBMs have

1260-414: A southern portion of the viaduct was removed at that time; the viaduct along the central waterfront remained open for traffic until the tunnel was complete. Boring of the tunnel with the 57.5-foot (17.5 m) diameter " Bertha ," at the time the world's largest-diameter tunnel-boring machine , began on July 30, 2013, and at the time was expected to be completed in 14 months. After three weeks of drilling,

1344-800: A speed and safety not previously possible. The Channel Tunnel , the Thames Water Ring Main , sections of the London Underground , and most new metro tunnels completed in the last 20 years worldwide were excavated using this method. EPB has historically competed with the slurry shield method (see below), where the slurry is used to stabilize the tunnel face and transport spoil to the surface. EPB TBMs are mostly used in finer ground (such as clay) while slurry TBMs are mostly used for coarser ground (such as gravel). Slurry shield machines can be used in soft ground with high water pressure or where granular ground conditions (sands and gravels) do not allow

1428-574: 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

1512-407: A two-year timeframe. 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

1596-432: A variable rate that changes based on time of the day, number of vehicle axles , and payment method. Tolls are collected electronically , with a lower rate for Good to Go pass users and a higher rate for scanned plates that are sent a bill in the mail. Tolling began on 9 November 2019, with the rate for two-axle vehicles set at $ 1.20 to $ 2.70 for Good to Go users and $ 3.20 to $ 4.70 for pay-by-mail users. The start of tolling

1680-411: Is 32 feet (9.8 m) wide and has two lanes in each direction. Each deck has two 11-foot (3.4 m) lanes, an 8-foot (2.4 m) west shoulder , and a 2-foot (0.61 m) east shoulder. The decks are designed with banks of two degrees in turns and four-degree grades to facilitate designed speeds of 50 miles per hour (80 km/h). Below the highway decks are utility lines and mechanical spaces for

1764-546: Is a smaller equivalent to a general tunnelling shield and generally bore tunnels of 1 to 1.5 meters (3.3 to 4.9 ft), too small for operators to walk in. Behind all types of tunnel boring machines, in the finished part of the tunnel, are trailing support decks known as the backup system, whose mechanisms can include conveyors or other systems for muck removal; slurry pipelines (if applicable); control rooms; electrical, dust-removal and ventilation systems; and mechanisms for transport of pre-cast segments. Urban tunnelling has

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1848-488: Is estimated to cost US$ 3.29 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: 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

1932-464: The Alps , Maus had it built in 1846 in an arms factory near Turin . It consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. The Revolutions of 1848 affected the funding, and the tunnel was not completed until 10 years later, by using less innovative and less expensive methods such as pneumatic drills . In

2016-525: The Battery Street Tunnel , which opened the following year, and several downtown ramps that were completed years later. The viaduct and tunnel cost $ 18 million to construct (equivalent to $ 162 million in 2023 dollars) and severed the waterfront from the rest of downtown. The viaduct remained the primary north–south highway in Downtown Seattle until the construction of Interstate 5 (I-5) in

2100-462: The Denny Triangle . The tunnel emerges at a portal located west of Aurora Avenue and north of Harrison Street, adjacent to a tunnel operations building. SR 99 continues onto Aurora Avenue and crosses over Mercer Street , while an onramp allows access to the tunnel from 6th Avenue and an offramp carries tunnel traffic to Republican Street in South Lake Union . The SR 99 tunnel is tolled with

2184-628: The Mersey River . The Hudson River Tunnel was constructed from 1889 to 1904 using a Greathead shield TBM. The project used air compressed to 2.4 bar (35 psi) to reduce cave-ins. However, many workers died via cave-in or decompression sickness. During the late 19th and early 20th century, inventors continued to design, build, and test TBMs for tunnels for railroads, subways, sewers, water supplies, etc. TBMs employing rotating arrays of drills or hammers were patented. TBMs that resembled giant hole saws were proposed. Other TBMs consisted of

2268-513: The SoDo neighborhood, adjacent to the Port of Seattle 's container ship terminal and the city's two outdoor sports stadiums, Lumen Field and T-Mobile Park . SR 99 enters the tunnel after passing Royal Brougham Way and an interchange with Alaskan Way at South Dearborn Street located adjacent to the south maintenance area and ventilation shaft. An additional set of ramps connect to South Royal Brougham Way and Colorado Avenue South, which terminates

2352-479: The Fréjus Rail Tunnel, by using less ambitious methods). Wilson's machine anticipated modern TBMs in the sense that it employed cutting discs, like those of a disc harrow , which were attached to the rotating head of the machine. In contrast to traditional chiseling or drilling and blasting, this innovative method of removing rock relied on simple metal wheels to apply a transient high pressure that fractured

2436-539: 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

2520-478: 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 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

2604-521: The Tuen Mun Chek Lap Kok link in Hong Kong. TBMs typically consist of a rotating cutting wheel in front, called a cutter head, followed by a main bearing, a thrust system, a system to remove excavated material (muck), and support mechanisms. Machines vary with site geology, amount of ground water present, and other factors. Rock boring machines differ from earth boring machines in the way they cut

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2688-519: The United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel in northwest Massachusetts. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine , after inventor Charles Wilson. It drilled 3 meters (10 ft) into the rock before breaking down (the tunnel was eventually completed more than 20 years later, and as with

2772-472: The caisson, requiring workers to be medically cleared as "fit to dive" and able to operate pressure locks. Open face soft ground TBMs rely on the excavated ground to briefly stand without support. They are suitable for use in ground with a strength of up to about 10 MPa (1,500 psi) with low water inflows. They can bore tunnels with cross-section in excess of 10 m (30 ft). A backactor arm or cutter head bore to within 150 mm (6 in) of

2856-410: The closure of the viaduct, sections of SR 99 were closed to traffic for three weeks to allow for the excavation of buried tunnel ramps at the north and south portals, as well as other preparations. The closure was widely expected to cause increased traffic congestion, and local government agencies responded by implementing expanded transit service and making other transportation changes to accommodate

2940-528: The construction of a tunnel under the English Channel and the British Parliament supported a trial run using English's TBM. Its cutting head consisted of a conical drill bit behind which were a pair of opposing arms on which were mounted cutting discs. From June 1882 to March 1883, the machine tunneled, through chalk, a total of 1,840 m (6,036 ft). A French engineer, Alexandre Lavalley , who

3024-439: The cutter head and extraction screw to ensure that the muck is sufficiently cohesive to maintain pressure and restrict water flow. Like some other TBM types, EPB's use thrust cylinders to advance by pushing against concrete segments. The cutter head uses a combination of tungsten carbide cutting bits, carbide disc cutters, drag picks and/or hard rock disc cutters. EPB has allowed soft, wet, or unstable ground to be tunneled with

3108-437: The cutter head of a TBM can be unpressurized, as the exposed rock face can support itself. In weaker soil, or when there is significant ground water, pressure must be applied to the face of the tunnel to prevent collapse and/or the infiltration of ground water into the machine. Earth pressure balance (EPB) machines are used in soft ground with less than 7 bar (100 psi) of pressure. It uses muck to maintain pressure at

3192-434: The cutter head to support the walls until permanent tunnel support is constructed further along the machine. The stability of the walls also influences the method by which the TBM anchors itself in place so that it can apply force to the cutting head. This in turn determines whether the machine can bore and advance simultaneously, or whether these are done in alternating modes. Gripper TBMs are used in rock tunnels. They forgo

3276-489: The cutting discs would travel over almost all of the rock face that was to be removed. The first TBM that tunneled a substantial distance was invented in 1863 and improved in 1875 by British Army officer Major Frederick Edward Blackett Beaumont (1833–1895); Beaumont's machine was further improved in 1880 by British Army officer Major Thomas English (1843–1935). In 1875, the French National Assembly approved

3360-400: The displaced drivers. Despite the predicted traffic congestion, commute times for the Seattle area were not significantly above average, with many commuters opting for public transit , remote work , or bicycling to work. On February 2, 2019, the downtown tunnel and sections of the viaduct and Battery Street Tunnel were opened to pedestrians as part of a community celebration and festival that

3444-506: The edge of the shield. After a boring cycle, the shield is jacked forward to begin a new cycle. Ground support is provided by precast concrete, or occasionally spheroidal graphite iron (SGI) segments that are bolted or supported until a support ring has been added. The final segment, called the key, is wedge-shaped, and expands the ring until it is tight against the ground. TBMs range diameter from 1 to 17 meters (3 to 56 ft). Micro tunnel shield TBMs are used to construct small tunnels, and

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3528-460: The end of the 19th century, speeds had reached over 30 meters per week. 21st century rock TBMs can excavate over 700 meters per week, while soil tunneling machines can exceed 200 meters per week. Speed generally declines as tunnel size increases. The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this

3612-438: The event of a fire, a set of fiber optic cables in the ceiling would sense heat and activate sprinklers . A set of large fans located in the two portal operations buildings would then force smoke out through a set of 40-foot (12 m) ventilation shafts. The tunnel also has repeaters for cell phone and FM radio service; WSDOT can override the latter for emergency broadcasts. The tunnel begins south of Downtown Seattle in

3696-489: The late 1960s. Weekday traffic volumes on the viaduct averaged around 110,000 vehicles per day in the mid-2000s, approximately half of equivalent sections on I-5. Calls to replace the viaduct and build a waterfront promenade surfaced as early as the late 1960s and early 1970s, increasing after the halted demolition of the Pike Place Market . The viaduct runs above the surface street, Alaskan Way , from S. Nevada Street in

3780-453: The left-side exits. Within days, reports of smoke and haze within the tunnel prompted WSDOT to investigate possible faults in the exhaust ventilation system. Within months of opening, tunnel usage had increased to over 70,000 trips per weekday and a weekly volume just under 500,000 trips by late March 2019. Tolls were waived for the first few months of operations and began to be collected on November 9, 2019. WSDOT measured traffic before and after

3864-411: The machine's main bearing had been damaged. Three days prior to stopping, the machine mined through a hollow, 8-inch steel well-casing and pipe used to measure groundwater in 2002 around Alaskan Way, which was drilled as part of the planning phases of the project. The unexpected discovery of the pipe was blamed by the contractor for the work stoppage in litigation, but STP later admitted to its knowledge of

3948-632: The new tunnel. The tunnel opened to northbound vehicular traffic at 11 p.m. on February 3 and southbound traffic at 12:15 a.m. on February 4. Other ramps and roads associated with the tunnel project, including an extension of Alaskan Way to Terminal 46 and the Harrison Street crossing were opened; the lone exception was the northbound offramp from SR 99 to Dearborn Street, which opened on February 19. The first full day of tunnel operations saw lower traffic volumes, with only 22,145 vehicle trips, due to an ongoing snowstorm, as well as confusion at

4032-418: 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 primary construction contractor was Seattle Tunnel Partners (STP). The initial phase of demolition and removal of the viaduct began on October 21, 2011, to prepare the southern portal. Only

4116-427: 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 Avenue 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

4200-479: The pipe's location prior to the start of tunnel boring. 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. Tunnel boring had resumed on December 22, 2015. The tunnel boring was halted 23 days later on January 14, 2016, after

4284-417: 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. Work was halted on December 6, 2013 after the machine overheated and shut down approximately 1,083 feet (330 m) into the planned 9,270-foot-long (2,830 m) route. Investigations later revealed the seal system that protects

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4368-407: The relative particle sizes of the muck. Slurry TBMs are not suitable for silts and clays as the particle sizes of the spoil are less than that of the bentonite. In this case, water is removed from the slurry leaving a clay cake, which may be polluted. A caisson system is sometimes placed at the cutting head to allow workers to operate the machine, although air pressure may reach elevated levels in

4452-585: The replacement of the Alaskan Way Viaduct had been the source of much political controversy demonstrating the Seattle process . Options for replacing the viaduct, which carried 110,000 vehicles per day, included replacing it with a cut-and-cover tunnel or a bored 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

4536-471: The rock. In 1853, the American Ebenezer Talbot also patented a TBM that employed Wilson's cutting discs, although they were mounted on rotating arms, which in turn were mounted on a rotating plate. In the 1870s, John D. Brunton of England built a machine employing cutting discs that were mounted eccentrically on rotating plates, which in turn were mounted eccentrically on a rotating plate, so that

4620-615: 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

4704-587: The special requirement that the surface remain undisturbed, and that ground subsidence be avoided. The normal method of doing this in soft ground is to maintain soil pressures during and after construction. TBMs with positive face control, such as earth pressure balance (EPB) and slurry shield (SS), are used in such situations. Both types (EPB and SS) are capable of reducing the risk of surface subsidence and voids if ground conditions are well documented. When tunnelling in urban environments, other tunnels, existing utility lines and deep foundations must be considered, and

4788-415: The start of tolling and reported a 26 percent decline in average weekday volumes in the tunnel, with no noticeable spike on nearby I-5. Higher volumes have been observed on Alaskan Way and other surface streets, especially during peak periods. In 2019, WSDOT began filling in the Battery Street Tunnel, because the 1952 cut-and-cover tunnel did not meet modern safety standards, was expensive to maintain, and

4872-540: The state government $ 60 million in extra costs that were granted by a budget increase from the legislature. The damage to the tunnel boring machine itself was estimated at $ 642 million, which became the center of a legal dispute between WSDOT and STP. Fragments of the steel well casing struck in December 2013 and cited as a possible cause of Bertha's breakdown were stored as evidence at the construction site and subsequently went missing in 2014. Detailed journal entries kept by

4956-439: The state transportation commission. The Alaskan Way Viaduct was a double-decked elevated freeway that ran along Elliott Bay on the Downtown Seattle waterfront and, until January 11, 2019, when it was permanently closed, carried a section of State Route 99 (SR 99). It first opened to traffic on April 4, 1953, to provide a vehicular bypass of downtown for U.S. Route 99 , the predecessor of SR 99; it connected with

5040-580: The tunnel contractor's deputy project manager between December 2013 and February 2014 also went missing. In December 2019, a jury in Thurston County awarded $ 57.2 million in damages to WSDOT and found that the state government was not liable to cover STP's claimed repair costs of $ 300 million. Seattle Tunnel Partners announced that work was substantially complete on the tunnel in October 2018. The viaduct closed permanently on January 11, 2019. Following

5124-588: The tunnel face. Main Beam machines do not install concrete segments behind the cutter head. Instead, the rock is held up using ground support methods such as ring beams, rock bolts, shotcrete , steel straps, ring steel and wire mesh. Depending on the stability of the local geology, the newly formed walls of the tunnel often need to be supported immediately after being dug to avoid collapse, before any permanent support or lining has been constructed. Many TBMs are equipped with one or more cylindrical shields following behind

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5208-401: The tunnel face. The muck (or spoil ) is admitted into the TBM via a screw conveyor . By adjusting the rate of extraction of muck and the advance rate of the TBM, the pressure at the face of the TBM can be controlled without the use of slurry . Additives such as bentonite , polymers and foam can be injected ahead of the face to stabilize the ground. Such additives can separately be injected in

5292-466: The tunnel following completion of the project's ongoing environmental review process. The referendum vote approved the City Council's actions by 58 percent on August 16, 2011. The Federal Highway Administration completed its analysis of the project's final EIS and issued its record of decision with WSDOT later that month, allowing pre-construction activities to begin. In January 2008, as debate on its replacement continued, Governor Gregoire announced that

5376-467: The tunnel to the voters as a citizen's referendum. The referendum was initially blocked by a lawsuit from the city, but was pared down to one aspect of the city's approval for the project and placed on the August 2011 ballot. Under the ruling, the referendum would only challenge one section of the original 140-page City Council ordinance that approved agreements over street use, utilities, design and liability for

5460-518: The tunnel's ventilation, lighting, and fire suppression systems. The tunnel has 15 emergency refuge areas located every 650 feet (200 m) with escape routes that lead to the north and south portals. Variable message signs and emergency phones are also located throughout the entire tunnel. The tunnel is monitored by over 300 security cameras that are fed into a WSDOT traffic control center in Shoreline that can dispatch incident response teams. In

5544-411: The tunnel, the way they provide traction to support the boring activity, and in the way they support the newly formed tunnels walls. Shielded TBMs are typically used to excavate tunnels in soil. They erect concrete segments behind the TBM to support the tunnel walls. The machine stabilizes itself in the tunnel with hydraulic cylinders that press against the shield, allowing the TBM to apply pressure at

5628-411: The use of a shield and instead push directly against the unreinforced sides of the tunnel. Machines such as a Wirth machine can be moved only while ungripped. Other machines can move continuously. At the end of a Wirth boring cycle, legs drop to the ground, the grippers are retracted, and the machine advances. The grippers then reengage and the rear legs lift for the next cycle. A single-shield TBM has

5712-468: 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

5796-640: 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

5880-405: 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

5964-498: 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

6048-463: 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

6132-656: Was about 62 GWh. It is owned and operated by the Italian construction company Toto S.p.A. Costruzioni Generali (Toto Group) for the Sparvo gallery of the Italian Motorway Pass A1 ("Variante di Valico A1"), near Florence. The same company built the world's largest-diameter slurry TBM , excavation diameter of 17.6 meters (58 ft), owned and operated by the French construction company Dragages Hong Kong (Bouygues' subsidiary) for

6216-587: Was also a Suez Canal contractor , used a similar machine to drill 1,669 m (5,476 ft) from Sangatte on the French side. However, despite this success, the cross-Channel tunnel project was abandoned in 1883 after the British military raised fears that the tunnel might be used as an invasion route. Nevertheless, in 1883, this TBM was used to bore a railway ventilation tunnel — 2 m (7 ft) in diameter and 2.06 km (6,750 ft) long — between Birkenhead and Liverpool , England, through sandstone under

6300-417: Was attended by 100,000 people. The celebrations included an 8K run , temporary art exhibits, food trucks , street performances, interactive exhibits, and an official ribbon-cutting ceremony. The following day, a bicycle race was held on the viaduct and in the new tunnel, with 12,000 participants. The state government also spent $ 4.4 million on billboards and advertisements on television and buses to market

6384-412: 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 would move in 6.5 ft (2.0 m) increments toward

6468-469: Was delayed by several months due to vendor issues and the viaduct demolition running behind schedule. Toll collection is expected to yield $ 22 million in annual revenue, which will cover 6 percent of the construction costs of the tunnel megaproject and its debts; the toll-collection vendor will be paid $ 16 million for system setup and $ 29 million over a five-year period. Beginning in 2022, the toll rates will increase by three percent annually with approval from

6552-420: Was dismantled and removed from the site over the next four months. Dirt produced by tunnel construction was sent to fill a CalPortland quarry in nearby Port Ludlow . In July 2016, WSDOT estimated that the tunnel would be 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. The delay in construction caused by Bertha's stall cost

6636-473: 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. On April 4, 2017, the tunnel boring machine broke through to the recovery pit on the north end of the tunnel, completing the excavation process. The boring machine

6720-1000: Was made redundant by the Alaskan Way tunnel. Tunnel boring machine Tunnel boring machines are an alternative to drilling and blasting (D&B) methods and "hand mining". TBMs limit the disturbance to the surrounding ground and produce a smooth tunnel wall. This reduces the cost of lining the tunnel, and is suitable for use in urban areas. TBMs are expensive to construct, and larger ones are challenging to transport. These fixed costs become less significant for longer tunnels. TBM-bored tunnel cross-sections range from 1 to 17.6 meters (3.3 to 57.7 ft) to date. Narrower tunnels are typically bored using trenchless construction methods or horizontal directional drilling rather than TBMs. TBM tunnels are typically circular in cross-section although they may be u-shaped, horseshoes, square or rectangular. Tunneling speeds increase over time. The first TBM peaked at 4 meters per week. This increased to 16 meters per week four decades later. By

6804-473: Was manufactured by The Robbins Company for Canada's Niagara Tunnel Project . The machine was used to bore a hydroelectric tunnel beneath Niagara Falls . The machine was named "Big Becky" in reference to the Sir Adam Beck hydroelectric dams to which it tunnelled to provide an additional hydroelectric tunnel. An earth pressure balance TBM known as Bertha with a bore diameter of 17.45 meters (57.3 ft)

6888-569: Was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods. The first boring machine reported to have been built was Henri Maus 's Mountain Slicer . Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through

6972-430: Was produced by Hitachi Zosen Corporation in 2013. It was delivered to Seattle , Washington , for its Highway 99 tunnel project . The machine began operating in July 2013, but stalled in December 2013 and required substantial repairs that halted the machine until January 2016. Bertha completed boring the tunnel on April 4, 2017. Two TBMs supplied by CREG excavated two tunnels for Kuala Lumpur 's Rapid Transit with

7056-464: 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%. Mayor Mike McGinn , elected in 2009 and opposed to highway expansion, joined other tunnel opposition groups to refer city council-approved agreements about

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