Cal Park Hill Tunnel

In 2008, Jacobs Associates was retained by Marin County in California to provide construction management (CM) services for the rehabilitation of the Cal Park Tunnel. The project’s unique dual focus is to rehabilitate the abandoned Cal Park railroad tunnel for light rail, and construct a pedestrian/bike pathway inside the tunnel. The refurbished tunnel will link the Marin County towns of Larkspur and San Rafael.

The tunnel is 1,100 feet long (335 m), 21 feet tall (6.4 m), and 26 feet wide (8 m), and was configured for double heavy rail track. It was constructed in weak shale and sandstone and mixed faced conditions of soil and rock. The tunnel was originally built in 1884, and the redwood timber ground support had decayed and weakened over time. Due to this deterioration, unstable rock conditions, and fires in the 1980s, the tunnel suffered collapse at the north and south ends. During earlier phases of the project, Jacobs Associates performed tunnel inspection and provided rehabilitation recommendations to various project owners.

Our more recent CM services include project management, resident engineering, field inspection, independent quality control testing, and office engineering. The tunnel was resupported with steel ribs, shotcrete, and concrete. To stabilize the tunnel at the north end, the project team installed a 100-foot-long (30 m) pipe canopy above the tunnel crown to provide confinement and reinforcement to the collapsed zone and act as a conduit to pump grout into the collapse debris. Additional grout was pumped from the surface above the tunnel using injection anchors, stabilizing the debris and allowing the contractor to excavate.

Project completion is estimated for 2010. The tunnel’s final configuration will allow commuters to either take the train or commute on their bikes.