When motorists take to San Francisco�s new $1-billion Presidio Parkway in late 2013, they won�t see some of the massive foundation piles placed deep into ground below. But they will feel the support of some of the largest cast-in-drilled-hole piles currently in use.
�The biggest challenge on this job from the beginning was a requirement to use 12-ft-diameter piles and [insert them with] very limited vibration because of historic buildings in the Presidio,� says Peter Faust, project manager for San Francisco-based Malcolm Drilling Co. �This meant we couldn�t use a pile driver with an impact hammer.�
To overcome this hurdle, Faust says the project team, led by the Caltrans and the San Francisco County Transportation Authority, had to find a company capable of inserting massive 12-ft-diameter piles without shaking the foundations of the nearby residents and 100-year-old historic buildings.
�They were looking around for alternatives and we happen to be one of the few companies in the United States that have machines that can install these [giant] casings without vibration by using our oscillator,� says Faust.
Stretching 1.5 mi, the Doyle Drive Replacement Project transforms a portion of Route 101 located within the Presidio of San Francisco into a new urban roadway called Presidio Parkway.
Originally built in 1936, Doyle Drive has been found to be structurally and seismically deficient and must be replaced. The new Presidio Parkway will be tucked into the natural contours of the Presidio and the Golden Gate National Recreation Area, one of the nation�s largest urban parks.
The road winds along the northern edge of the city and connects the San Francisco Peninsula to the Golden Gate Bridge and the North Bay. Each weekday, more than 100,000 vehicles travel between Marin and San Francisco over the Golden Gate Bridge along Doyle Drive.
Presidio Parkway will create a spectacular regional gateway between the Golden Gate Bridge and the city of San Francisco. Construction began in December 2009 and substantial completion is expected in 2013.
Design highlights include two sets of tunnels spanning 1,017 ft and 853 ft, respectively; a wide landscaped median giving motorists the experience of traveling through a park while taking in views of the bay or Presidio; and numerous pedestrians and bicycle crossovers.
Besides above ground features, the project is highlighted by giant 12-ft-diameter foundation piles below.
Malcolm is currently installing the piles for a new viaduct, with a unique 90-ton oscillator machine called the Leffer VRM 3800, which is made in Germany.
�The oscillator is a very unique tool,� says David Pang, construction manager for Caltrans. �This 12-ft-diameter one is the largest on the planet that we know of.�
The longest piles going in are nearly 200 ft-long. To get them inserted to the required depth of 170 ft they must first be spliced into three pieces and welded together once in the ground. The pieces are then lifted by a 300-ton crane and set on the oscillator where they are cork screwed into the ground by two arms with hydraulic jacks. While the machine pushes the piles into the ground, it also grabs and excavates soil from the middle.
�Getting these cages up in the air without bending or destroying them was a challenge because we had to develop new lifting gear and procedures to align the cages properly and pour them,� says Faust, adding that the rebar cages weighed up 150-tons. �And we spent quite a bit of money doing this.�
Funded in part by $168 million from the American Recovery and Reinvestment Act, the Presidio Parkway is being constructed using eight separate and phased contracts.
To minimize traffic disruption, the first phase involves construction of new structures adjacent to the existing Doyle Drive so that the roadway can remain open.
�We�ve planned the construction phase to minimize disruptions to traffic,� says Jos� Luis Moscovich, executive director of the San Francisco County Transportation Authority. �We will first build the southbound structures, then, in 2011, transfer traffic onto these completed structures and a temporary bypass while we demolish the old road and build the new northbound portions.�
The first major construction contract of $48.4 million was awarded to C.C. Myers in November 2009 to construct the new southbound viaduct bridge. In March, Walnut Creek-based R&L Brosamer Inc. was awarded a $57.7 million contract to construct a temporary bypass, a southbound tunnel and a section of permanent roadway. The first two contracts cover environmental mitigations and utility relocation, with contract two won by Ghilotti Bros. of San Rafael.