I-80 Overhead Road Signs – Donner Pass, CA

Hillside Drilling was awarded a contract to drill and install foundations for new overhead road signs along Interstate 80 near Donner Pass, California. The plans called for 5-foot diameter, 25-foot deep cast-in-drilled hole caissons. The contractor encountered resistant granitic rock at depths of 5 to 6 feet in several of the holes, which would have required the blasting and removal of competent rock to construct the foundations as specified in the project plans. Holdrege & Kull was contracted to determine if an alternate design could be prepared, which would take advantage of the resistant rock encountered on-site, rather than requiring costly rock excavation. H&K developed a reinforced mat foundation utilizing four tension anchors in the corners of the foundation. Caltrans approved the design, and we understand that Caltrans continues to use this foundation approach on other projects.