Presidio Parkway Project
(In the City and county San Francisco on Route 101 from 1.3 mile South to 0.4 mile North of Route 101and Route 1 Separation)
The Presidio Parkway project replaces Doyle Drive, a 1.6-mile segment of Route 101 in San Francisco that is the southern access to the Golden Gate Bridge, connecting Marin and San Francisco counties and providing a primary regional traffic link between the peninsula and North Bay Area counties. Built in 1936, Doyle Drive was found to be structurally and seismically deficient. In April 2012, traffic was shifted onto a seismically safe temporary bypass that would carry traffic until the roadway replacement was completed in 2015. The project was not only critical for seismic and traffic safety, but it also provided an opportunity for significant design improvements. The project is a collaborative effort by the California Department of Transportation (Caltrans), the San Francisco County Transportation Authority, and the Federal Highway Administration. Flatiron is the design-build lead for Golden Link Concessionaire, LLP, which, under the P3 contract, will design, build, finance, operate, and maintain the project for 33.5 years.
Because the construction site was in a National Park area with uncertain marine soil conditions and numerous historical buildings, including 100-year-old army structures, the Deep Soil Mixing (DSM) technique was adopted instead of pile-driving, which could cause vibration damage to nearby structures. DSM was used for ground stabilization and excavation support with an average depth of 27.4 ft. and a maximum depth of 105 ft. under the future roadway and Main Post Tunnels to prevent settlement or liquefaction during a seismic event.
Project Highlights
Deep Soil Mixing (DSM) was used for ground stabilization and excavation support walls.
Six-axle DSM equipment was used to depths up to 105 feet. Two DSM mixing rigs were used with a single shift.
The installation of the DSM wall was completed on time and within a very tight schedule.
DSM construction exceeded the unconfined compressive strength and soil mix uniformity design requirements. The spacing of DSM walls varied the design specifications for the unconfined compressive strength of shear walls.