Rhonda Pence

8/14/2019 Rhonda Pence

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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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http://www.seattle.gov/http://www.seattle.gov/

Rhonda Pence

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