LADWP City Trunk Line Sequential Excavation Method Tunnel underneath the Tujunga Wash

The Los Angeles Department of Water and Power’s City Trunk Line Sequential Excavation Method (SEM) Tunnel Project consisted of the planning, design, and construction of a 252 foot-long, 10-foot diameter tunnel that needed to navigate through and around bridge abutment piles 60 feet below the ground surface that supports the major intersection and Tujunga Wash above. SEM tunneling was selected to provide the engineers with more control during the construction process, to allow for modifications to be made based on actual tunneling conditions, and to utilize the strength of the surrounding ground to provide optimized support for the tunnel. The tunnel excavation was carried out in short increments, where fiber reinforced shotcrete was sprayed onto the exposed soil immediately following excavation. A 60 inch trunkline was installed in the tunnel after completion, as part of the larger City Trunk Line Project, which involves replacing over 9 miles of riveted steel pipe that was installed in 1914.