Construction has begun on Phase II of the Presidio Parkway Project in the heart of San Francisco’s Golden Gate National Recreation Area. The $1.4 billion endeavor is the first public-private partnership transportation project delivered in California under the state’s recently enacted PPP statute.
Construction involves the replacement of out-dated Doyle Drive with a new, state-of-the-art roadway.
"This world-class project will not only improve earthquake safety, it will also support jobs and preserve the natural, cultural, and recreational resources of the Presidio," Caltrans Director Malcolm Dougherty said in a statement.
Built in 1936, Doyle Drive was found to be structurally and seismically deficient. In April of 2012, traffic was shifted onto a seismically-safe temporary bypass that will carry traffic until the replacement of the roadway is complete in 2015. Official say the project is not only critical for seismic and traffic safety, but it also provides an opportunity for major design improvements.
Led by a design-build joint venture between lead contractor Flatiron, along with Kiewit Construction, the aging Doyle Drive has been re-envisioned as the Presidio Parkway—a roadway tucked into the natural contours of one of the nation's largest urban parks and a former military base. The parkway is designed to create a spectacular regional gateway between the iconic Golden Gate Bridge and the city of San Francisco.
This second and final stage of the project includes the construction of three cut-and-cover tunnels, seven bridges, the High Viaduct, and the Girard Road interchange.
Bud Tolp, deputy project manager with Flatiron, says one of the biggest project challenges is keeping traffic flowing on the Highway 101 and through the Presidio, while constructing the new roadway. He says by working with local transportation agencies, crews are successfully detouring motorists through an area used by more than 120,000 vehicles each day.
Because they are working in a National Park area with uncertain marine soil conditions, as well as numerous historical buildings, monuments and possible prehistoric artifacts, crews are not using any kind of pile-driving for foundations. Instead, the team is using a cement deep soil mixing (CDSM) technique.
At the east end of the project, where tunnels will be constructed near the water, there are layers of sedimentary rock and bay mud which goes down about 30 ft, says Tolp.
“We are using the CDSM ground technique to improve the soils so they will respond accordingly for the loads placed on them by structures and seismic demands,” he says.