Mission Valley East Extension

Client

San Diego Association of Goverments

Completion Date

2004

Designer

Zimmer Gunsul Frasca

Location

San Diego, California

Delivery Method

General Contractor

Division

Underground

Contract Value

$105 million
Mission Valley East Extension

Constructed under and through the San Diego State University campus, the 4,000-foot SDSU Tunnel and Station connects to a 5.9-mile Mission Valley East extension development project, known as the Green Line. This project provides a vital trolley connection between Mission Valley and East County San Diego, connecting the blue and orange transit lines. As part of the project, a 14-ton arched suspension bridge was erected across six lanes of College Avenue and serves as a main pedestrian entrance to the campus from parking and dormitories. The San Diego Tunnel and Station consist of four main areas: the west box, approximately 900 feet of open cut and cover box culvert construction; the tunnel, approximately 1,070 feet of sequentially mined and constructed using the New Austrian Tunneling Method (NATM); the station, approximately 670 feet of open cut and cover box support of excavation to provide for the construction of the main station; and the east box, approximately 1,000 feet of open cut and cover box culvert construction.  The trolley station platform is a 50,000 SF soaring space highlighted with a serpentine brick paved pattern as designed by a local artist. The station includes multiple other artistic elements including 'Tap Roots' sculptures in the station and etched botanical images. The opening of the SDSU Tunnel and Station offers a cost-effective, viable solution to the parking/traffic problems that have plagued the campus community.

Atkinson excavated the tunnel utilizing NATM mining, making it the second-largest diameter tunnel in the U.S. The transit tunnels are of a twin-box construction separating east and westbound trolleys. Atkinson used multiple crews and worked 24 hours a day, seven days a week to excavate the 37-foot-wide, 29-foot-high tunnel. Atkinson performed a total of 2,915 linear feet of cut and cover excavation and an additional 1,085 linear feet of NATM underground tunnel excavation.