SR-128 Rockslide Repair DO (EA 4X570)

Caltrans proposes repairing a rockslide that occurred on SR-128 in Sonoma County at PM 4.859. Severe winter storms caused rockfalls and slip outs due to oversaturation of the slope above the highway. Given the site conditions and continuing slope movement, immediate repair of the slope is necessary before the upcoming winter storm season causes further failure. Two landslide occurred at this location. The first occurred along the eastbound embankment slope and can be described as a shallow cut slope failure that is approximately 70 feet wide by 50 feet long by 3 feet deep. The second is also along the eastbound embankment slope and can be described as a shallow cut slope failure that is approximately 200 feet wide by 50 feet long by 3 feet deep. The Caltrans Office of Geotechnical Design recommends installing an anchored Double Twisted Wire Mesh (DTWM) system to control rockfall at the site. This system will be designed to hold rockfall in place on the slope since there is little to no catchment at the base of the slope. Prior to the installation of the anchored DTWM, the loose material on the slope shall be removed and the brow of the slope shall be graded to match adjacent slopes. Slide materials will be temporarily stockpiled in nearby vehicle pullout areas and will be hauled off and disposed or at a nearby facility. The existing ditch line will also be re-established. Traffic control will be required during construction, as well as construction area signs, portable message signs, and temporary k-rials.