This project was part of CADOT’s development of Caldecott’s 4^th bore tunnel on Highway 24 that links the East Bay Valleys and Bay Area. Excavation was performed in the most adverse ground conditions of the tunnel, where a mélange of sandstone, siltstone, and fault materials were identified in the first 200′. The SEM drifts were advanced through an incremental two-pass approach that enabled the appropriate excavation through these faulted zones. Temporary shoring was also performed at the portals as the site location historically experienced landslides.  

There were several challenging aspects to Caldecott’s construction that included compliance with stringent environmental regulations, specially tailored equipment for tunnel safety, and third-party considerations. For instance, blasting was specifically prohibited because of the tunnel’s CalOSHA gassy classification and the existing structures nearby. Drill Tech maintained the proper protocol for the project’s safety and successful completion.