The Last Chance Grade Project is a collaborative effort to study alternatives for a permanent solution to instability and roadway failure on a 3-mile segment of US Highway 101 in Del Norte County. The area in question extends from Wilson Creek to 9 miles south of Crescent City. Project Partners are considering alternatives that provide more reliable connections through the region; protect economic, environmental, and cultural resources; and reduce maintenance costs.
Crux was subcontracted by Kleinfelder to provide core drilling and sampling in difficult-to-access locations and challenging subsurface conditions. Crews drilled 11 geotechnical borings at varying inclinations, ranging in depth from 100 to 300 feet; a total 2,689 feet of drilling was completed. Seven borings were accessed by track drill rigs and four required helicopter portable drill rigs due to the steep slopes and dense underbrush. Testing and instrumentation included Standard Penetration Testing (SPT), permeability testing, pressure meter testing, suspension logging, downhole imaging, and multi-level vibrating wire piezometer (VWP) and inclinometer installations.
All borings included in Crux’s scope were in active landslide conditions and known faults. Related drilling challenges included loss circulation zones as well as working through fractured, displaced and unstable materials. Crux developed drill fluid program and provided experienced tooling selection that aided in borehole stabilization, sample recovery, and successful completion of all borings to design depth.
Additional project challenges included poor weather and visibility, which caused delays in helicopter supported work. Crux implemented overnight security so the helicopter could be kept onsite, minimizing standby time and reducing impacts to the overall project schedule. Drilling successfully provided high-quality data to the client and was completed in a safe, efficient manner.