Construction of the Richmond Transport Tunnel in San Francisco encountered extremely variable and difficult geologic conditions, ranging from strong Franciscan Complex graywacke to saturated dune sand. Successful completion of this 10,200-foot-long tunnel in 1996 was a significant achievement that required both hard-rock and soft-ground tunneling methods. An accurate understanding of the geologic conditions, based on a thorough pre-construction geologic exploration program conducted along the tunnel alignment, was critical in planning and constructing this important project. Another challenge
was the need to minimize construction impacts in this sensitive urban setting. This paper describes the geologic explorations conducted for the project, the anticipated geologic and ground conditions, and the tunneling methods used to construct the tunnel.