|The foam blocks are lightweight fill for the abutments. They will be capped with concrete to protect them from surface oils and salts.|
Additional pictures provided by NYSDOT.
After a 2004 bridge inspection found that a crack had appeared in one of the fascia girders on the westbound bridge of Interstate 690 in Syracuse, New York, the bridge's right lane was immediately closed until emergency repairs could be made to stabilize the structure and allow it to safely carry traffic. Further inspection revealed that the outdated structural design features that led to the crack were present in all nine fascia girders. With 76,500 vehicles a day traveling in both directions on the bridge, and as many as 70 trains a day traveling beneath the bridge, the New York State Department of Transportation (NYSDOT) determined that a complete bridge replacement was necessary.
An accelerated project development and design was undertaken, and the project was let in November 2006. NYSDOT awarded the $20-million contract to Vector Construction Corp. of Cicero, NY, and on January 12, 2007, work began.
According to Kurt Bower, P.E., NYSDOT engineer-in-charge in Region 3, the first day on the project began with capping the work site due to industrial pollutants and waste found in the area — some of which had been used to build I-690's embankments. Soil testing of the existing embankments revealed that a byproduct of the soda ash process — a white chalky material known as Solvay waste — and 54 chemicals were present in the soil, which had a high pH of 11 or 12.
"For employee safety we actually capped the site where equipment would be stored and the men would be working," says Bower. "We put in 6 inches of sub-base, a geotextile, and then 6 more inches of sub-base. This prevented contaminated soil from blowing around and causing a (health) problem."
Work then proceeded on constructing the temporary crossovers that would allow traffic to be diverted onto the eastbound bridge so that the westbound bridge could be demolished and constructed. Pavement work on the median areas had actually been added to a 2006 emergency contract by NYSDOT; however, some embankments remained to be built. Vector Construction brought in sub-base with a higher percentage of aggregate in the material in order to stabilize it during placement and construction. After paving the temporary median, traffic was switched to the eastbound bridge.
To prepare the westbound bridge for demolition, Vector had paint removed from locations where cuts in the girders were to be made. The paint contained asbestos and lead, so the process took six weeks in order to ensure compliance with strict environmental regulations.
Demolition of the existing westbound bridge began with removal of the concrete deck. Moving east to west, the deck was saw cut into panels for removal with a hydraulic hammer and Vermeer saw. The concrete panels were taken to a nearby site for crushing, and the aggregate was reused as embankment on the job site.
After the bridge and substructures were demolished, two abutments and three piers were removed, including the original footings.
Remediating the poor soils has been a challenge throughout the project. In the 1950s when the original bridges were built, sand drains were installed and the area was surcharged to minimize settlement. During construction of the eastbound abutment, the elimination of an extra span required filling in the area with embankment material. However, in order to avoid adding extra weight to the existing subsurface material, which would have led to settlement, Expanded Polystyrene foam blocks from Thermal Foams, Inc. in Syracuse, NY, have been used as lightweight fill.
Both new bridges also feature a hanging back wall, a design that eliminates joints in the deck. Bower explains that the back wall is poured in two stages. The first stage of the backwall is poured and then backfilled with embankment and/or foam blocks. The structural steel is erected and then the second stage of the backwall is poured. The top portion of the backwall "hangs" off the structural steel, which is an integral part of the wall. The second stage backwall is then backfilled with embankment and/or foam blocks. The foam blocks are then capped with concrete to protect them from petroleum products (oils and gasoline).
The team also ran into a challenge during construction of the bridge piers. There is a stream going through the site, so Vector had to span a box culvert with one of the pier footings. The box culvert was so high that it would have been into the pier stem wall as originally designed. NYSDOT had to redesign the pier and raise the footing elevation so the stem wall could be above the box culvert. In addition, all of the other piers feature a crash wall and columns. Bower points out, "Because we had to raise this pier up so much to accommodate the culvert, the columns would have only been 2 feet tall. That's why we have a full pier here instead of a set of columns. It would have been difficult to form otherwise."
The construction team completed the westbound bridge in November 2007, and traffic was diverted onto it to begin work on the eastbound bridge this year. There has been no staged construction, so traffic management has been crucial.
"These bridges are very close to the state fairgrounds," says Josh Ribokove, public information officer for NYSDOT Region 3. "Every summer during the 12 days of the state fair, close to a million people go through there, so managing and protecting traffic is really important. What we've done is shift traffic so you have two lanes going in each direction at all times. Our construction people are working off the roadway that's being used. We brought out a lot of gear from our transportation management center and other places across the state (to help control traffic)."
Construction on the eastbound bridge is tentatively scheduled for completion in September, and all contract work should be finished by October — well ahead of the original completion date of December 31, 2008.