The Office of Geotechnical Design West (OGDW) provides expert Soils and Foundations recommendations for structures and roadways throughout the Western Service Region of California. The Service Area for OGDW is corresponds to District 4 and the State Toll Bridge Program.

BRANCH CHIEFS

SENIOR SPECIALISTS

SAMPLE CURRENT PROJECTS

San Francisco - Oakland Bay Bridge
04-ALA,SFO-80

The San Francisco-Oakland Bay Bridge (SFOBB) carries 280,000 vehicles of traffic per day across San Francisco Bay. During the 1989 Loma Prieta earthquake, the east span of the bridge suffered considerable damage, including the collapse of one section of the upper deck. A series of subsequent studies determined that the existing structure did not meet present-day seismic safety standards for the region, and it would be more cost-effective to replace the east span of the bridge than it would be to retrofit it.

The proposed new bridge will be constructed along a parallel alignment to the north of the existing bridge. The new bridge will be approximately 3.8 kilometers (2.3 miles) long and include a 565-meter-long, single-tower, self-anchored suspension cable, “ signature span” and a 2.1-kilometer-long “Skyway” structure. The geology of the bridge was extensively mapped by Geotechnical Services through drilling explorations conducted from barges. The majority of the new bridge foundations will be founded on large 1.8 to 2.5-meter diameter, approximately 60- to 100-meter long pile foundations. The ability to install the mammoth piles, designed to hold compression loads up to 140MN, was confirmed through a recently-conducted on-site pile installation demonstration project. The first of three construction contracts was awarded in January 2002 and construction of the replacement span is scheduled to begin early Summer 2002.

Landslide Repair on Sonoma Coast on Highway 1

The Office of Geotechnical Design West was contacted to provide Geotechnical expertise for a major landslide on the Sonoma County Coast along Highway 1 at Post Mile 30.3 (KP 48.8). Significant landslide movements had compromised the existing tieback wall at Shotgun Curve, located near Timber Gulch. The Geologists and Engineers of Geotechnical Design West worked in conjunction with Structures Design staff to design a permanent geotechnical solution.

A very complex landslide history and the close proximity of the San Andreas Fault (0.3 km west of project) made this a challenging project. The roadway will be moved approximately 30 meters inland behind the head scarp of the landslide. In order to accomplish this, the construction of a 20-meter high soil nail wall and the excavation of approximately 45,000 cubic meters of material were required. In addition, a new tieback wall is being constructed on the outside shoulder of the new highway alignment to prevent the current landslide scarp from encroaching on the new roadway.

I-80 Carquinez Bridge Replacement Project
04-CC, SOL, KP 0.7/1.8

The ambitious construction of the New Carquinez 1-kilometer long suspension bridge to replace the existing 1927 westbound steel truss bridge is currently under way. To facilitate the roadway widening for the bridge approaches, a series of temporary and long-term retaining walls required design and construction, with heights up to 25 m. Geotechnical Design West performed field investigations, type selection studies, geotechnical studies, groundwater monitoring, plans and specifications generation, and construction support throughout the project.

A number of standard soil nail and soldier pile walls were developed on north approach. In addition, The north anchorage excavation, as seen in the photo, was developed up to 25 m depth below the adjacent high voltage PG&E towers. This wall incorporated a combination of very high capacity post-tensioned strands and standard soil nails. The geology of the sites is very complex and consists of very weak and steep adversely bedded rock. A water-bearing fault, which crosses the NE corner of the site, also imposed a considerable challenge during the construction of the excavation shoring for the bridge north anchorage.

The bridge south approach project included development of the New Crockett Interchange and widening of the westbound I-80 up to Cumming Skyway. A number of standard, soil nail and soldier pile tieback walls were developed for the Interchange and the south approach roadway widening. Of a particular interest was a 21-m short-term and 18 m permanent tieback wall aligned along Wanda Street in Crockett, as seen in the photo. The primary purpose of this wall is to provide stability during construction for the residential covered hills overlooking the strait. The wall also serves to control the creep in the weak and weathered rocks and to allow construction of 6-lane on- and off-ramps structures. Geotechnical Design West performed complete soil-structure interaction analyses for the stability and deformation of this wall to confirm the design. The presence of the nearby Franklin Thrust Fault, swelling and slaking soft rock, and a congested project site have made this project both unique and challenging.

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Last Updated April 7, 2005

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