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The Alaskan Way Tunnel
Project
Rhonda PenceCM510
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Table of Contents
Brief History andOverviewpp. 3-4
Boring
Machine.pp.
5-8
Alaskan WaySeawall.pp. 8-10
Alaskan Way
Promenadep. 10
Conclusion.p. 11
Sources
.p. 12
Exhibits:
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
The
Gribble
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
ground.
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
diameter.
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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
ft.
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
methods.
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
out.
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
forward.
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, semi-annualinspections show that Coleman Dock and the Viaduct across from
Coleman Dock continue to settle. The inspection reports state theViaduct has settled a total of 5.5 inches since the earthquake.
The length of seawall slated to be redesigned and built is 3,750 ft.
between Washington and Pine Streets. Last month the city council
appropriated $225M for the project. Additional sections of the
seawall will have to be replaced eventually.
Theres a timing issue associated with work on the seawall. In-
water work cannot be done during the February to June fish
window. And due to commercial concerns, construction along the
promenade needs to be limited during the summer tourist season.
Design and planning of the seawall are currently in progress.
Materials, shapes and textures are being studied to establish
what is best for the marine habitat. Eighteen test panels were
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installed in 2008 and UW will be studying how the marine life
responds. The results will help to inform the final design of the
seawall face.
Alaskan Way Promenade
The Promenade is expected to break ground in 2017, once the
Viaduct has been demolished. The plan is to pave a new, wider 4-
lane Alaskan Way where the Viaduct is now, which will result in a
wider, more pedestrian friendly promenade. The projected
amount to be spent on this part of the project is currently $400M.
Artists rendering of the Alaskan Way Promenade
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Conclusion
This report has described the Alaskan Way Project, which major
components are the bored tunnel, the seawall replacement andthe Alaskan Way Promenade. The overall project also includes
street and transit improvements.
The Alaskan Way Viaduct was showing signs of age in the 1990s
before the Nisqually earthquake of 2001. It is now quite
vulnerable. Compromised joints have been sistered with steel
beams, but its hard to imagine how it can survive until 2016-
2017 when the tunnel is estimated to be complete.
The seawall is a major component in the Viaducts vulnerability,
and construction on it is slated to begin in 2011. Alaskan Way
and the Viaduct across from Coleman Dock continue to settle
about .5 inch a year. The area is closely monitored and repairs
are ongoing.
Whatever decision Seattle made to replace the Viaduct would be
a defining one, which was probably a factor in the eight years of
studies and more studies. Ultimately, the decision was ambitiousand visionary. The tunnels most ardent supporter was voted out
of the mayors office last month, but legislation to begin the
project was signed into law in May by the governor.
A perfect storm, of sorts, is gathering. With the nation in a
recession and the states unbalanced budget concerns, will the
tunnel project be completed according to plan, especially with
almost certain cost overruns? And the biggest question is will
the tunnel be operational before the next big earthquake.
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Sources
Alaskan Way Viaduct & Seawall Replacement Project Draft
Environmental Impact Statement (RebuiltAlt_tabloid.pdf) (2006)
The Tunnel Hybrid Solution for Alaskan Way Viaduct Project
(Reilly-White-02102009-2-attch1.pdf)(January, 2009)
Patent Storm Tunnel Boring Machine with Crusher US Patent6017095 Description (January, 2000)
Seattletimes.nwsource.com SR99 Bored Tunnel Access (2009)
The Alaskan Way Viaduct & Seawall Replacement Program
Bored Tunnel Briefing Dec. 16, 2008
The Alaskan Way Viaduct & Seawall Replacement Program
Central Waterfront, 99 Corridor Coalition, March 26, 2009
Seattle PI Lawmakers Approve Tunnel to Replace Viaduct
(April 25, 2009)
AbsoluteAstronomy.com History of Boring Machines
WSDOT map of Bored Tunnel Alternative (2007)
WSDOT map of Project Area (Sept., 2009)
WSDOT Alaskan Way Viaduct Semi-Annual Inspection Results February, 2001 October, 2009
WSDOT- Draft Description of Potential Hybrid Scenarios (Dec. 15,
2008)
WSDOT Projects/Viaduct (2007-2009)
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Wikipedia Alaskan Way Seawall
www.seattle.gov Alaskan Way Seawall Project Passes Major
Hurdle (Oct, 2003)
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