South Slough Bridge #91 2008 APWA National Project of the Year Transportation Category, Projects Less Than $2 million
South Slough Bridge #91 Snohomish County Public Works Art Louie P.E., Engineering Services Director Larry Brewer P.E., Project Manager CRAB Conference – October 7, 2009 APWA “Project of the Year” for 2008
Location Located 4 miles west of Arlington Near I-5 exit 208 Carries Smokey Point Boulevard over South Slough
Background Part of the Pioneer Highway built by State North Arch built in 1918 South Arch built in 1920
Background 80-feet spans Arch built in 1918 Luten style concrete arch Founded on wood piling
Problem Functionally Obsolete by 2005 5000 vehicles daily 19-feet between concrete rails Many sideswipe accidents
Decision Improve bridge deck to 28-feet width. Preferred over replacement with new bridge. New Bridge: 28 feet Existing Bridge: 19 feet Existing Arch
Decision Improve bridge deck to 28-feet width. Preferred over replacement with new bridge. REASONS: Safety improvement 85 year-old arch structure was basically sound. Preserves historic structure. Minimize impact to wetlands and flood plain. Affordable with no supporting grants. Less $ and time than full replacement.
Project Engineering The Luten arch foundation was sound. However two requirements had to be met: Minimal or no dead load increase to reduce risk of settlement. The wider design had to maintain same dead load distribution as the original structure. Parsons Brinckerhoff was tasked with resolving the structural engineering.
Widen Without Weight New deck would be precast concrete slabs. Each slab was 8’ x 31’ x 1’ 32 slabs total 43,000 pounds each slab 950,000 pounds total of new structure! PLAN
Widen Without Weight We needed to replace earth fill (125 pcf) with lighter material that could still transfer loads to the arch.
Widen Without Weight 2 materials were considered for light weight fill. Geofoam would be extremely light at 2 pcf. Difficult to custom form and assure good load transfer to arch. Cellular concrete or “Engineered Fill” ranges in density from 30 to 110 pcf. Compression strength varies from 40 to 2400 psi. Can be formed in place. 1000 CY of Elastizell cellular concrete was used. We needed to replace earth fill (125 pcf) with lighter material that could still transfer loads to the arch.
Balancing Act Removed existing concrete slab. Partially removed the existing parapet; used the remaining portion as a form for the new light-weight concrete fill. Removed the existing soil fill in uniform lifts, alternating from one arch to the other to maintain a balanced distribution of weight. A correct load distribution and a well-planned construction sequence were essential for the success of this widening project.
Construction Sequence Filled arches with lightweight concrete in uniform lifts, again alternating from one arch to the other. Added a layer of crushed rock to serve as the base for the new pre-cast concrete slabs. Laid the 32 pre-cast slabs on top of the crushed rock, working from the center outward. Added a lift of asphalt and new galvanized steel bridge rail system.
Community Coordination • Developed detour plans • Coordinate with WSDOT • Newsletter distributed • County website • Newspaper display ad • Specific coordination for the Annual Arlington Fly-In • 50,000 people for one week!
Schedule 17 months from start of design to end of construction During scoping decision was made to have County forces construct project. Time saved by working together as design-build team Design began................. April 16, 2006 Design finished............... April 15, 2007 Ad date......................... April 23, 2007 (for pre-cast concrete, cellular concrete, bridge rail, crane) Construction began......... June 25, 2007 (road closed) Construction finished....... September 12, 2007
Schedule Time Saving Measures: Early coordination with utility companies during the design phase and continued coordination throughout the project. Underground water and sanitary sewers were avoided by modifying excavation at abutments. The design team stayed with the project through construction and provided support to the construction inspector. The County’s Road Maintenance personnel built the bridge, eliminating the need for a lengthy bid process. Parsons Brinckerhoff, a County on-call consultant, was utilized to prepare the structural engineering.
Safety There were no injuries on the South Slough Bridge construction project. Daily tailgate meetings were held each morning to discuss the plan for the day—work to be done and safety measures to be followed during the process. Crew members wore proper safety equipment. The construction manager attended monthly safety meetings. All of the County’s construction managers meet monthly as a group with the County’s safety trainers and report back to their project crews. All members of the crew had CPR and First Aid training. Defensive driving certification was also required. Some crew members also had confined space training.
Saving $$$ It was determined at the scoping meeting that reusing the arches could save time and money. The average cost of a new bridge in Snohomish County is: Construction - 423 $/SF Engineering, ROW, Contract admin. - 159 $/SF Total cost for new bridge - 582 $/SF Bridge 91 had a total cost of 129 $/SF
Saving $$$ It was determined at the scoping meeting that reusing the arches could save time and money. Nearly $5,000,000 saved!
Key Points Final Project Cost: $929,100 Cost of total replacement would have been approximately $6 million. Saved $5 million. Duration: 17 months Typical bridge replacement of this magnitude takes approximately 6 years. Using original arch foundation shortened project by 1.5 years. On Schedule Scheduled 55 days for construction. Completed in 55 days, on September 12, 2007.
Key Points Good Construction Management Techniques Critical path method schedule was developed and followed. Design and construction staffs stayed in close communication throughout the project. Safety: No Injuries Daily field meetings and monthly department safety meetings promoted a safe construction site. Community Relations County staff maintained direct interaction with stakeholders and utilized internet, mailings, a newspaper ad and flashing message boards to minimize impacts to the community.
Key Points Environmental Protection Reusing the existing arches kept construction out of the wetlands and out of the floodplain. Banks were re-vegetated with native shrubs.
Unusual Accomplishments New 62% larger deck area did not add weight to the arches. This was the largest bridge project constructed by County Road Maintenance crews. Reusing existing arches reduced project duration by approximately 4.5 years. To prevent overloading the arches, earth fill within the arches was replaced with light-weight cellular concrete.
Unusual Accomplishments To prevent unbalanced loading of the arches, soil was removed incrementally from both sides of the bridge. 32 precast concrete slabs, 8 feet by 31 feet, were placed side by side and bolted together above the existing arches and cantilevered 4.5 feet on each side. The crew lost less than 2 hours of productivity when bones were unearthed. The archeological consultant was on site early the next morning and identified them as cow bones.
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APWA National Congress New Orleans, August 2008