US Army Corps of Engineers Ellio by pengtt

VIEWS: 41 PAGES: 23

									            Pacific Northwest Waterways Association
               2008 MID-YEAR MEETING



        Puget Sound Update:
      The Elliot Bay Seawall and
         Swinomish Channel
                  Mona Thomason
        Chief of Planning, USACE, Seattle District

                     Tom Szelest
Navigation Business Line Manager, USACE, Seattle District
US Army Corps of Engineers
     Elliott Bay Project
    The Alaskan Way Seawall
Before the Seawall – Railroad Ave.




   Seattle Waterfront 1931
         Seawall Construction
In the mid-30’s, Seattle
  built a concrete wall,
  secured by a 60’ wide
  timber tie-back
  structure, and placed
  fill, to create Alaskan
  Way.
Seawall Construction
          The timber was
            untreated, but was
            expected to be
            protected from marine
            borers by the steel
            and concrete face
            wall. The risk and the
            solution were both
            noted at the time.
         Seawall Construction
The seawall supports
  the fill that the surface
  street and the Viaduct
  are built on. The
  strength of the
  seawall is in the
  timber tie-back. The
  concrete and steel
  that is visible would
  collapse without the
  tie-back.
          February 28, 2001
         Nisqually Earthquake
• The Puget Sound area was shaken by a
  magnitude 6.8 earthquake at around 11:00 a.m.
  on February 28, 2001. The quake was located
  32 miles below ground, about 35.7 miles south
  of Seattle, and lasted about 45 seconds.
• The earthquake was felt as far away as Salt
  Lake City, and caused widespread damage to
  buildings, roads, and bridges, including the
  Alaskan Way viaduct in Seattle.
                          •   Earthquakes
                          •   Current structures cannot withstand another earthquake

Urgent Need               •   Gribbles and Teredos are eating the seawall

                          •   Safety
                          •   Weight restrictions and inspections are required




Regardless of the alternative, the central seawall must be replaced.
               City Response
• The earthquake prompted
  the City to inspect the
  seawall for damage. The
  road had settled near the
  Aquarium due to
  liquefaction, a result of
  the earthquake.
• Inspection of the seawall
  revealed extensive
  damage and deterioration
  that preceded the
  Nisqually earthquake.
Gribbles
    • Test pits revealed that
      gribbles have been
      consuming the timber
      tie-back structure.
    • Gribbles are marine
      borers, microscopic
      marine life that
      consumes wood.
    • The usual protection
      against borers was
      creosote.
           The Risk to Seattle
Failure of the seawall would
  cause extensive disruption
  to the economy.
• 110,000 vehicles per day
  on Alaskan Way Viaduct
• 12,000 vehicles per day on
  Alaskan Way surface street
• 30,000 passengers per day
  use the Colman Ferry
  Terminal
The Risk to Seattle
          • The waterfront is a major
            utilities corridor serving
            downtown Seattle and the
            region.
          • 24 freight trains and 6
            passenger trains per day
            travel the waterfront.
          • The waterfront is a major
            tourist destination.
      Condition of the Seawall
• The seawall was built prior to recognition of the
  Puget Sound as a seismic risk area. Even in
  new condition it would not meet modern seismic
  code.
• If the Nisqually quake was longer, more
  liquefaction could have caused the wall to fail.
• Deterioration due to gribbles continues. The
  seawall is not expected to last another 50 years,
  even without another quake. Eventually, enough
  of the timber will be lost and parts of the wall will
  begin to fail.
               The Solution
The City is pursuing
  complete replacement
  of the old seawall.
Options include
  combinations of large
  concrete drilled shafts
  and injected grout.
  Costs may reach $1B.
Engineering studies are
  currently in progress.
                 Study Overview
• Atypical Corps Project
   – No past storm damage events
   – Seawall planning and design well advanced by local partner
   – WRDA 2007 added seismic damage prevention to authority,
     allows City to work ahead of Corps

• Project Phases
   –   Reconnaissance – Feasibility – PED – Construction
   –   Feasibility study estimated at $9.5 million
   –   $4.0 million in work accomplished so far
   –   Federal appropriations = $2.074M 2004-2008
       Study Accomplishments

• Advancement of without project condition
• EIS scoping meeting
• Participated in AWVSR outreach events
• Phase 1 environmental/HTRW site assessment
  completed
• Sampling for cultural resources study
• EIS baseline conditions reviewed, nearly
  complete
    Way Forward – Best Case
• Complete new no-action/without project
  condition analysis this winter
• Feasibility Scoping Conference next spring
• Alternatives Formulation Briefing, early
  2010
• Final EIS/Feasibility report, early 2012
• PED phase, 2 years
• Construction, 2014
Seawall - Habitat Test Panels
  Background Information - Seawall




Corrosion Led to Street   Gribble Attack on Timber Platform
  Collapse in 1954
Background Information - Seawall

          Proposed Repair – Option 1
Background Information - Seawall

         Proposed Repair - Option 2
  +           20’   10’
  16
                                  +9
                          1             #18 Bar Anchor

                              2        Casing pipe @ 5.33’ o.c.
  Similar
  to Type A
  wall
                                                 Till @ Seneca St.



                                       Temporary
                                       Shoring Wall
                                       as Required
Before the Seawall
         The Seattle waterfront
           was occupied by
           Railroad Avenue, a
           dangerous, wooden
           planked street on
           piles over Elliott Bay,
           until construction of
           the seawall.
            Pacific Northwest Waterways Association
               2008 MID-YEAR MEETING



        Puget Sound Update:
      The Elliot Bay Seawall and
         Swinomish Channel
                  Mona Thomason
        Chief of Planning, USACE, Seattle District

                     Tom Szelest
Navigation Business Line Manager, USACE, Seattle District

								
To top