Ground Stabilization | Geotechnical Constru
Devil's Slide Twin Tunnels
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Project Description
The Devil's Slide project consisted of constructing twin tube tunnels beneath San Pedro Mountain in San Mateo County, California. When completed, the 30-foot wide, 650-foot below ground tunnels will extend to lengths of 4133 feet and 4035 feet. The north and southbound tunnels will provide realignment for a section of Route 1 close to the coastline that is known for frequent closures due to rockslides and land slippage. In 2009, the project received recognition as the Association of Engineering and Environmental Geologists Project of the Year.
The tunnels will be completed using the New Austrian Tunneling Method and are expected to be in service by 2013.
Team Members
California Department of Transportation, Kiewit Pacific Company, Crux Subsurface Inc.
Crux’s Role
Crux provided the installation of dewatering wells at the North Portal for both the north- and southbound tunnels of the project. Ground conditions in the area were considered to be particularly unsound and Crux drilled to challenging lengths in the unstable and fractured environment.
Two pumped dewatering holes were drilled to lengths of 540 feet and 690 feet, parallel to the tunnel's decline. Additionally, one gravity dewatering hole was drilled at an incline to a length of 645 feet. Crux obtained surveys of all boreholes during drilling to ensure corrective action was not necessary. An HQ3 triple tube coring system was employed to minimize deviation, which Crux successfully kept to +/ 2 degrees despite the difficult conditions.
Pumped holes were reamed to 6 inches and the gravity hole was reamed to 4 inches using a rotary bit hole opener. All holes were successfully drilled while working in extremely close proximity to another contractor installing tiebacks. Crux installed slotted 4-inch PVC pipe in the pumped holes and 2-inch PVC pipe in the gravity hole, along with subsequent pumps and wiring. All pipes, pumps, tubing and electrical materials for the three dewatering holes were sourced and installed by Crux.
To request additional information, please use our Contact Page or call 866-CRUXSUB (866-278-9782).
