Dewatering Well Drilling
The project included construction of twin tube tunnels beneath San Pedro Mountain in San Mateo County, California. The tunnels rerouted a section of Route 1 known for frequent closures due to rockslides and land slippage. They were completed using the New Austrian Tunneling Method, and are the second and third longest tunnels in California, measuring 4,149 feet and 4,008 feet.
California Department of Transportation
Kiewit Pacific Company
Crux installed dewatering wells at the North Portal for both the northbound and southbound tunnels. 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. One gravity dewatering hole was drilled at an incline to 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.
The 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.