SR-116 Monte Rio Slipout Repair DO (EA 0V510)

SR-116 Monte Rio Slipout Repair DO (EA 0V510)

The California Department of Transportation (Caltrans) proposes repairing a slipout that occurred on State Route (SR-) 116 in Sonoma County at post mile (PM) 6.77, 1 mile east of the Russian River Sidehill Viaduct, in the community of Monte Rio, just east of Duncan Road. The slipout was caused by a series of rain events from December 22, 2025 to January 5, 2026, and is approximately 80 feet long, 30 feet wide, and 40 feet deep toward the Russian River. Field Maintenance crews closed the affected eastbound direction of the highway, while the westbound lane remains open with one-way traffic control. A temporary sheet pile wall approximately 75-feet-long and 5-feet-wide was immediately constructed to stabilize the roadway. Temporary rock slope protection (RSP) was placed to prevent erosion. Permanent repair of the roadway and embankment will start by removing the temporary sheet pile wall that was installed immediately after the slipout occurred. Caltrans will protect and isolate the active worksite by developing a containment system (e.g., plywood wall, fiber rolls, and waterproof structure with a pump running below the construction area) to ensure no construction pollutants or runoff reaches the Russian River. Debris, loose material, and vegetation on the slope will be cleared and grubbed. Several trees that were made hazardous as a result of the slipout or will conflict with the emergency repairs will be removed. The project will construct a permanent soldier pile wall with concrete lagging and tiebacks. The soldier piles will be spaced at 6 feet on center and extend 50 feet deep. An access road will be constructed so that equipment and personnel can drill the piles into the ground. The native slope will be reconstructed with RSP and a keyway per recommendations from the Office of Geotechnical Services West. The RSP will be backfilled where possible with native material and topsoil to support vegetation growth, and the reconstructed embankment will be compacted to 95 percent to accommodate a new guardrail. Portions of the reconstructed roadway embankment will use gabion baskets for support. These gabions will be fully covered with soil-filled landscaping baskets further supporting vegetation growth. Permanent erosion control measures will be installed on the slope to prevent further erosion and slipouts. The drainage systems will be reconstructed per Hydraulic recommendations and will include removal and replacement of 60 feet of a damaged corrugated steel pipe (CSP) downdrain, installation of a G2 inlet on the eastbound shoulder, installation of a grated line drain (GLD) to intercept surface runoff from Duncan Road and convey it ot the existing ditch, and regrading and cleaning of the drainage ditch. The roadway will be reconstructed by excavating, backfilling, and then repaving the surface. Pavement striping and delineation will be replaced. One-way traffic control using a portable traffic signal system is required during construction.

Unincorporated Sonoma County (Monte Rio)

Sonoma

Northern California, San Francisco Bay Area

Sonoma