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  • 8/14/2019 Rhonda Pence


    The Alaskan Way Tunnel


    Rhonda PenceCM510

  • 8/14/2019 Rhonda Pence


    Table of Contents

    Brief History andOverviewpp. 3-4




    Alaskan WaySeawall.pp. 8-10

    Alaskan Way

    Promenadep. 10

    Conclusion.p. 11


    .p. 12


    Map of Tunnel

    Route/Soil..p. 4

    Expected Roadway Design within

    Tunnelp. 5


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    Timeline Boring Machine

    Sizesp. 6

    Boring Machine similar to expected forProject.p. 7

    Rendering of Current

    Seawall..p. 8



    p. 9

    Rendering of Future

    Promenadep. 10


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    The Alaskan Way Tunnel Project

    The Alaskan Way Viaduct, which is an elevated part of SR 99, was

    built in 1953. It runs along the Elliott Bay waterfront and often

    carries over 100,000 cars per day.

    During the 1990s, inspections of the Viaduct revealed crumbling

    and cracking concrete, exposed rebar, weakened column

    connections, and deteriorating railings. It was reaching the end of

    its useful life.

    In 2001, an earthquake occurred in Nisqually, located

    approximately 30 miles south of Seattle, which damaged the

    already compromised Viaduct. Also, liquefaction occurred under

    the seawall, which runs parallel to the Viaduct. The earthquake

    registered 6.8 on the MMS and lasted 45 seconds.

    After several commissioned studies, three different

    recommendations were proposed to replace the Viaduct. A

    decision was made January, 2009, to build a bored tunnel from

    the Battery Street Tunnel to SoDo. This tunnel will be

    approximately two miles long and one of the longest tunnel

    highways in the U.S.

    Tunnels can be designed as one of the safest places to be during

    an earthquake. This is because ground movements below thesurface are much smaller than the amplified, or whip-lash,

    movements above the surface. Also the tunnel moves with the


    Actual construction of the tunnel will begin in 2010, although

    electrical lines are currently being relocated. The estimated finish


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    date for the tunnel is 2016 at the cost of $1.9B. Then the rest of

    the project, which includes replacing the seawall and upgrading

    the waterfront promenade, is estimated to conclude by 2019 for a

    total project cost of $4.24B.


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    The tunnel will run under 1st Avenue which is several blocks inland

    from where the Viaduct is currently located. It will pass through

    glacial till 60-200 ft. below the surface. Advantages for boring at

    this depth are the improbability of much environmental and

    archeological impact, as well as avoidance of abundant old

    timbers and contaminated soil.

    Seattle can draw on experience from other countries which have

    built projects similar to the Alaskan Way Tunnel. The Shanghai

    Yangtze River, in China, includes two bores, each about 5 miles

    long with a 50.6 ft. diameter. Fourth Elbe River Tunnel in

    Germany is a single bore 2 miles in length and 46.6 ft. in

    diameter. And Madrid M30 in Spain which includes bores 5 miles

    in length and 49.9 ft in diameter. Tunnel boring technology hasbeen developing at a rapid rate as more projects are completed.

    The Seattle project will require a machine approximately 54 ft. in



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    The design of the roadway

    within the tunnel will be similar to the existing Viaduct. There will

    be two lanes of traffic southbound on the upper level roadway

    and two lanes of traffic northbound on the lower level roadway.

    The tunnel will include passageways to safety in case ofemergencies and a ventilation system if needed. There will be

    one 2 ft. shoulder and one 6-8 ft. shoulder. Clearance will be 16


    Tunnel Boring Machine

    The tunnel boring machine was invented as an alternative to

    drilling and blasting methods of rock and hand digging of soil.

    Boring also produces a smooth tunnel wall and doesnt have as

    much environmental impact. And, as in the Seattle project,

    tunnels can be bored deeper, into more stable soils, than the old

    conventional methods.


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    The very first boring machine ever reported to have been built

    was in 1845 by Henri-Joseph Maus. It used percussion drills

    mounted in the front of a locomotive-sized machine, mechanically

    power-driven from the entrance of the tunnel. By the time thetunnel was finished 10 years later, the drills had been changed to

    pneumatic type.

    In 1853, the first boring machine was built in the U.S. to construct

    the Hoosac Tunnel in Florida. The machine broke down every 10

    ft. due to drilling through mountain rock. After 25 years and the

    loss of 195 lives, it was finally completed using traditional


    In the early 1950s James Robbins made the single most

    innovative change to the tunnel boring machine. He introduced

    the rotating head. It bored 160 ft. in 24 hours which was 10 times

    faster than its predecessor. Robbins machine was built to tunnel

    through shale, so when it was used on other materials it did not

    perform as well.

    After the success of Robbins machine, boring became a viable

    technology and considerable money was spent on research.Cutting rates grew from 600 ft. a month in the late 1960s to as

    much as 4,000 ft. a month in 2004.


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    Nowadays, boring machines are unique to their intended use, but

    the following is a general description of the technology. A tunnel

    boring machine (TBM) consists of a large metal cylinder (shield)and trailing support mechanisms. At the front end of the shield is

    a rotating cutting wheel. Behind the cutting wheel is a chamber

    where the excavated soil is mixed with slurry to be transported


    Behind the chamber there is a set of hydraulic jacks which push

    the TBM forward, like an earthworm. The rear section of the TBM

    is braced against the tunnel walls and used to push the TBM head


    Behind the shield, inside the finished part of the tunnel are the

    support mechanisms. These comprise the dirt removal system,

    slurry pipelines, control rooms, and rails for transport of the

    precast concrete sections. The cutting wheel will rotate at 1 to 10


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    rpm depending on the material, cutting the rock face into chips

    and/or excavating soil (muck). The muck will be mixed with slurry

    and pumped back to the tunnel entrance. In the meantime,

    precast concrete sections are moved up and into place, thuslining the tunnel.

    A boring machine similar to what Seattle will use.

    Different soils require different TBM heads. The Alaskan Way

    Tunnel will be going through glacial till, for the most part. Glacial

    till is an unconsolidated mixture of clay, sand, gravel and

    boulders. At the time of this writing, the TBM has not yet been

    manufactured. Soil samples to a depth of 100 to 300 ft. have

    been taken every 100 to 400 ft. and are currently being analyzed.

    Alaskan Way Seawall

    As stated before, liquefaction occurred to the soil under the

    seawall during the Nisqually earthquake of 2001. Liquefaction


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    occurs when, under loading, soil transitions from a solid state to a

    liquid state. Loading, in this case, was the movement of the earth

    which is supporting the seawall.

    The Alaskan Way Seawall runs 7,000 ft. along the Elliott Bay

    waterfront. There are actually a series of seawalls to buffer

    against the waters of Elliott Bay. It was built on top of wood

    pilings in 1934 to extend the waterfront and make it easier to

    load and unload the many ships which sail into the Port of Seattle.

    The seawall is built from wooden platforms, sheet steel piling,

    unreinforced concrete and dirt. Hundreds of steel panels were

    linked side by side over 50 ft. from the shore to form a barrier.

    Next, thousands of wooden pilings were driven into mud to form

    the foundation for Alaskan Way. Soil was placed to fill in thevoids from the water to the top of the pilings. Then a timber

    platform was laid on top, connecting the wooden piers and the

    steel seawall. A layer of dirt, 12 ft. deep, was laid atop the

    platform, on which the street was constructed. Alaskan Way,

    between Bay and Washington Streets, is actually a timber bridge.


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    In addition to the problem of liquefaction under the seawall, there

    is also an issue with gribbles chewing the pilings. A gribble is a

    crustacean 1-4mm long which bores into wood and plant material

    for ingestion as food. They are known for causing damage topiers, but also help to breakdown driftwood. Inspections have

    shown that a significant amount of the timbers have been

    weakened or destroyed by gribbles.

    Microscopic image of L. Limnoria,commonly known as the Gribble.Gribbles have substantially contributedto the seawall's deterioration.

    After the earthquake a 100 ft. long by 10 ft. wide section ofAlaskan Way settled. Since the earthquake,