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Devil's Slide Tunnels

Construction inspection and scheduling for initial and final liner and waterproofing; analysing monitoring data and project's progress; daily site inspection and ground conditions reports.
Estimated cost: Commencement:
November 01, 2007
Completion date:
March 01, 2011
585 Linda Mar Boulevard
Pacifica, CA 94044
United States
Technical data:
Geology description:

The geological setting comprised quartz diorite, marine sandstone, conglomerate and clay-siltstone. Four main fault zones were encountered.

Geology types:
Bid cost: Final cost:
$273 million USD
Service areas:
Construction methods:
Groundwater control:
Tunnel length:

Devil's Slide is located south of the City of Pacifica in California along the coastal road of Highway 1. Landslides and grade subsidence in the Devil's Slide area along Route 1 have led to the road being closed for extended periods causing significant economic loss to the surrounding communities. The solution: Construct a tunnel through the mountain to bypass the dangers and reoccurring problems. Construction of 1250m twin tunnels, 9m wide, 6.8m high using Sequential Excavation Method (SEM). Additionally, drill and blast and roadheader excavation through weathered rock utilised.

Drill jumbo drilling blast holes in top heading advance face
Finished southbound tunnel with textured cast-in-situ concrete
Tunnel Portals
Aerial view of completed portals