California taxpayers are getting their money's worth on the Benicia-Martinez Bridge work, east of San Francisco, with minimal traffic disruption. The $37-million rehabilitation is a joint venture between Top Grade Construction and American Civil Constructors (ACC) for this Caltrans project. The work will ease traffic congestion on the existing southbound I-680.
Top Grade is realigning both the 680 & 780 Freeway ramp approaches to the Benicia-Martinez Bridge as well as constructing a bike lane that will connect Benicia with Martinez.
"We will be demolishing three smaller bridges on the north side of the main span," says Eric Ronning, senior project manager of Top Grade. "At the south end of the bridge (the Undulation Area) ACC is driving sheet piles for shoring and Top Grade is going to excavate down 15 feet below original grade, which happens to be 6.5 feet below sea level." This is a challenge requiring an elaborate dewatering system.
"Since many of the bid items on this job are billed by volume, GPS technology is helping to show Caltrans how much material we have moved," Ronning said. The 'Undulation Area' is a 40-year-old portion of I-680 that was constructed on less than ideal soils.
Phase 1: ACC — remove and replace all NB truss bridge expansion joints, shoring undulation area excavation, construct new median slabs between NB and SB bridges, place cellular concrete in the excavated undulation area, demo old toll plaza facilities, build two retaining walls, polyester paving over all bridge surfaces (Benicia-Martinez Moccoco bridge).
Phase 2: Shore undulation area excavation, replace all SB truss bridge expansion joints, full-depth removal and replacement of a section of SB bridge deck 12 feet wide by 4,892 feet long (starting in the fall 2008), jacking and raising one half of Moccoco bridge to match the slope on the other half, construction of new barrier rails with fence for a bike path on the existing bridge, and removal of three existing bridge structures.
"Access is a huge factor," says Dave Horn, general manager for ACC. "This is an existing bridge structure approximately 170 feet high above the Carquinez straits. The only way to access the bottom of the deck is via moving travelers suspended under the bridge from structural traveler rails. The travelers are operated by compressed air. The existing intricately constructed steel truss bridge provides challenges to protection from falling debris during demolition and new construction."
Another challenge was to figure out a solution to drive steel sheet piles through depths of asphalt up to 12 feet for shoring, he added. ACC used the combination of trencher and an ABI hydraulic pile installation machine to solve that issue.
"Due to the constant settlement and subsequent repaving over the years, there are sections of asphalt up to 12 feet thick," adds Ronning. "Once the asphalt is removed, the remaining excavation is performed by an excavator and trucks. The materials have been pre-classified by the state as containing low levels of contamination from hydrocarbons and air-deposited lead, therefore the material has to be removed, stockpiled and sampled to determine the nature and levels of the contaminants."
"Innovative forming methods such as materials light enough to be handled by individuals have to be used," Horn continued. "We've used multiple travelers and creative work methods to sustain various activities, such as installation of debris shields, form rotation, concrete placement, curing and stripping to manage a tight schedule."
"After the traffic switch at the conclusion of stage one, work will begin on the southern portion of the bike path on the Martinez side," said Ronning. "Additionally, work on Marina Vista Avenue will be underway to correct a drainage problem that has resulted in localized flooding during the rainy season." The new finished grade will be approximately two feet higher than the existing grades.
"We're using a fairly new method to reduce the loads on the bay mud by using cellular concrete. Cellular concrete consisting of lightweight cement paste mixed with cellular polymer will be placed in a cell approximately 1,000 feet long by 36 feet wide with depths up to 15 feet. It will be a new item for everyone on the project," said Horn.
"Access will continue to be an extreme challenge," Horn re-emphasized, "As is making sure the false-work support system being utilized won't affect the railroad below."
Estimated completion is in June 2009.