Devil's Slide Tunnel Update August 2009

Project Update

Contractors at the Devil's Slide project are making progress. Recently, the two bridges connecting the North Portal with Highway 1 were completed and while probing and dewatering programs are implemented from the North Portal to mitigate groundwater inflows during the upcoming tunneling, two roadheaders constantly dig their way forward coming from the South.

Tunnel excavation is continuing and the Contractor is preparing for the start of waterproofing and final lining installation works.

To date, more than 50% of the twin 4200ft (1.25km) Devil's Slide tunnels have been excavated by the roadheaders and occasional drill & blast excavation. In the Northbound Tunnel the excavated length has reached 2530ft (770m) and 2430ft (740m) in the Southbound Tunnel. Bench and invert excavation is currently approximately 160ft (50m) lagging behind.

Geology

After the moderately strong to strong cystalline igneous rock, named quartz diorite of the "South Block", tunneling is currently taking place in three major lithology types: sandstone, siltstone/claystone and conglomerates. This formation is called "Central Block". Later this year, when excavation is progressing further, the "North Block" will be encountered. It consists of sandstone, siltstone/claystone, and interbedded layers of sandstone, siltstone and claystone. Four inactive faults that intersect with the tunnel alignment of the project will be handled by utilizing grouted pipe spiling and pipe roof umbrellas.

Project Participants

The construction of the twin highway tunnels was awarded by the Client, California Department of Transportation (Caltrans) to Kiewit in 2007.

DSC in JV with URS is performing construction inspection and scheduling services. These are carried out for the construction of the portals, the tunnel excavation, installation of support elements, initial and final liner construction and the waterproofing system. DSC is responsible for analyzing monitoring data and documenting the project's progress, including daily site inspection reports, ground conditions encountered, monitoring data, and installation of support elements.