The tunnel runs generally east-west across the north end of San Diego County. The west terminus is a shaft 100' deep, the east terminus is a portal, and two additional shafts are in between, with depths of around 75'. Depth of tunnel varies according to the surface topography, but can be as great as 600'. The tunnel encounters varying geology, ranging from extremely hard granitic rock near the ends, to loosely cemented conglomerate in between. Some of the conglomerate may also be tightly cemented. The water table is below the tunnel for approximately half its length, at the "peaked" middle section of the alignment.

Due to the varying geology, multiple tunnel methods have been chosen. Two open face shields, equipped with excavator arms and replaceable road header type attachments, are mining the conglomerates.

These shields were manufactured by Construction Tunneling Service. A refurbished Robbins mainbeam machine is mining the rock sections at each end. Conventional excavation methods have been used in a section of tunnel which interfaces the rock and conglomerate in an unpredictable fashion. Drill and blast methods, combined with sequential excavation method type techniques, were used.  

At present, the Portal, Slaughterhouse Shaft, Central Shaft, and West Shaft have been completed. Reaches 3, 4 West, 5 and 6 excavation is complete, as well.  Excavation continues with both CTS Shields and the Robbins TBM.

Project Gallery:

Construction Method:
Start Date: Notice of Award 07/01/05; Notice to Proceed 07/14/05
Completion Date: In Progress
Owner:San Diego County Water Authority, San Diego, California
Joint Venture: Traylor/J. F. Shea