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SEM Tunneling for Chinatown Station and Crossover Caverns

San Francisco Municipal Transportation Agency (SFMTA)

Phase 2 of the Third Street Light Rail Project is currently underway, which includes the construction of the Chinatown Station, cavern, crossover and cross-cut caverns using the Sequential Excavation Method (SEM).

Expert Review Services:

Gall Zeidler Consultants provides expert design review services on the SEM tunneling for the Chinatown Station and associated  SEM caverns, which includes review and recommendation of the following aspects of the work: construction staging, multiple drift excavation sequencing, structural design calculations, use of ground improvement measures for dewaterwing and grouting, settlement mitigation measures involving compensation grouting, structural design calculations, instrumentation and monitoring, waterproofing, contact packaging, and SEM specifications.

Location:

San Francisco, California

Date:

2009 – Present

Structure:

Mined Underground Center Platform Stations with Ancillary Caverns

Length:

Cross Cut Cavern 2,700 square feet (250 square meters)
Station Caverns 2,300 square feet (213 square meters)
Cross Over Cavern 1,750 square feet (163 square meters)

Cross-Section:

Cross Cut Cavern 67 feet (20 meters)
Station Caverns 290 feet (90 meters)
Cross Over Cavern 310 square feet (95 meters)

Geology

Highly Deformed Fractured Rock, (Melange, Franciscan Rock Formation), Colluvium Consisting of Very Stiff, Brown and Gray Silty Clays, Old Bay Deposits, Sedimentary Marine Deposits, Fluvial Deposits and Fill

Cost:

Approximately $1.5 Billion

Client:

PB Americas / Wong JV

Owner:

San Francisco Municipal Transportation Agency (SFMTA)