Caldecott Tunnel

The California Department of Transportation contracted Drill Tech to excavate a bore tunnel on Highway 24 to link the East Bay Valleys and Bay Area. The contract consisted of drilling, setting beams, pouring concrete, installing permanent wood lagging for exposed shoring, and constructing soil nails with an anchored-wire mesh rock slope protection system. During the excavation process, Drill Tech also drilled support beams, installed tie-back walls, and provided secant pile and tie-back shoring at the tunnel portals.

Throughout the project, Drill Tech maintained the proper protocol for project safety, complied with stringent environmental regulations, tailored our equipment to ensure project safety, and kept third-party considerations in mind. Due to the tunnel’s gassy classification designated by Cal/OSHA, Drill Tech was prohibited from blasting, which complicated the excavation process. In addition, the ground conditions were extremely adverse, as sandstone, siltstone, and fault materials were all identified within the first two hundred feet of excavation. To mitigate these issues, Drill Tech advanced SEM drifts through an incremental two-pass approach that enabled proper excavation through faulted zones. Temporary shoring was also constructed at the tunnel portals, as the project location was historically prone to landslides.