Allison Ranch Road Landslide Mitigation – Nevada County, CA

Over the course of several days in April 2006, a sizable landslide resulted in significant cracking, settlement, and closure of Allison Ranch Road south of Grass Valley. The slide mass also flowed into Wolf Creek downslope from the roadway. Holdrege & Kull performed a geotechnical investigation of the landslide, which included drilling borings through the landslide mass, installing slope inclinometers and TDR cables in the borings, excavating several exploratory trenches, and performing slope stability analyses of the slide above and below Allison Ranch Road. As a part of the investigation, H&K evaluated options to mitigate the slide and also reviewed a proposed realignment of the road. H&K has continued to provide routine long-term monitoring of the landslide.