Cal Park Tunnel Holes Through

June 03, 2009 - The Cal Park Hill Tunnel project reached a major milestone when, on Wednesday, May 27, 2009, the tunnel holed through. The project has a dual focus: rehabilitation of the existing Cal Park railway tunnel for light rail, and construction inside the tunnel of a pedestrian/bike pathway. The refurbished tunnel will link the Marin County towns of Larkspur and San Rafael.

The tunnel had collapsed at the south end, requiring re-mining and support installation through disturbed and heterogeneous rock and soil, with rock blocks up to two to three cubic yards. The project team installed a 100-foot-long pipe canopy with two-foot, on-center spacing above the tunnel crown to provide confinement and reinforcement to the collapsed material and act as a conduit to pump grout deep into the material. Additional grout was pumped from the surface above the tunnel using injection anchors. Both approaches were highly successful in stabilizing the muck and allowing the contractor to proceed along most of the length of the collapsed zone with a vertical heading. The south heading was first visible from the north through an approximately 20-foot-long void in the rocks on May 8, 2009. The last of the muck pile, grout, and shotcrete were mined in the morning of May 27, and access through the tunnel was possible as of that afternoon.