Presidio Parkway P3 Project
The Presidio Parkway project is a replacement of 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 major 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 of 2012, traffic was shifted onto a seismically-safe temporary bypass that will carry traffic until the replacement of the roadway was completed in 2015. The project was not only critical for seismic and traffic safety, but it also provides an opportunity for major 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, as well as numerous historical buildings, including 100-yr-old army structures, 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 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 excavtion support wall.
- Six-axle DSM equipment was used to depths up to 105 feet. Two DSM mixing rigs were used with a single shift.
- Installation of DSM wall was completed on time within a very tight schedule.
- DSM construction exceeded unconfined compressive strength and soil mix uniformity design requirements. Design specifications for unconfined compressive strength of shear walls varied with the spacing of DSM walls