In 2010, responding to a, existing state law that requires unimpaired passage for all anadromous fish at stream crossings, Caltrans prepared a priority list for replacement projects. The existing Forth Goff Creek Bridge, which was a 15 feet (4.6 m) diameter structural steel plate culvert, no longer met code. Indeed, the old design received the lowest rating for fish passage because the drop-off from end of the culvert to the creek water level prevented salmon from spawning further upstream.
In response, Caltrans decided to replace the 60-year-old pipe culvert, with a new 60 feet (18 m) long, single-span, precast, prestressed concrete voided slab bridge. To minimize disruption, they went with an accelerated bridge construction method that enabled them to deliver the project in just 78 working days.
By choosing a precast concrete design and accelerated bridge construction process the replacement project had little impact on the traveling public. It also resulted in fewer disturbances to the environmentally sensitive site, allowing the channel section and streambed beneath the highway to be restored to a more natural state.
To achieve the aesthetic goals of the project, the prefabricated wing wall elements feature architectural texture and staining to mimic the natural stone at the project location, and the exterior deck panel beams were cast with a curb for an attractive see-through bridge railing.
To reduce transportation costs, the abutments were modularized in three sections at 42.5 ton (378 kN) each, and were then assembled using a grout and posttensioning system. Keeping the pick weights under 47.5 ton (423 kN) avoided the need for a specialty crane. The pieces were detailed to fit against each other with narrow keyways filled with grout and posttensioned transversally. Each abutment has at least two piles to ensure they are self-supporting and stable.
The resulting bridge blends seamlessly with the environment, and allows the stream to flow naturally so that salmon can once again spawn upstream in the Fort Goff Creek.