According to the graphic depicting progress on tunneling, work crews have excavated more than 300 meters. The graphic shows mining of the topheading at the eastern and western portals of the tunnel.
Breaking through a three-foot thick concrete retaining wall, tunneling crews began excavation on the western side in mid-March, as work on the eastern side continued to make headway. Excavation of the Orinda Formation has been completed and tunneling through the Claremont Foundation is well underway.
Tunneling from the west presents new challenges. The less stable rock formation requires the installation of structural reinforcements at shorter intervals than on the eastern side.
