The purpose of the project is to implement emergency repairs in order to prevent the loss of the highway due to roadway fill displacement and associated culvert failure along the portion of State Route 101, at PM 97.12, in Mendocino County. The highway in this location is supported by log cribbing. Fill was placed upslope of the horizontal logs until the desired road grade was reached. The log cribbing at this location reached a height of approx 30 ft and incorporates the outlet of a culvert at PM 97.12. Since the cribbing is supported by adjacent growing redwood trees, the existing fill slope is near vertically inclined. Due to the age of the lob cribbing, the logs have either rotted through or have been broken due to the soil loading conditions. As such, road supporting fill is exposed, unsupported, eroding, and locally slumping. The culvert at PM 97.12 outlets in the upper ½ of the log cribbing, and is shot gunned. The free falling outflow from the culvert is eroding/undercutting the toe of the log cribbing. Given the ground movement, the culvert that is buried in the fill has decoupled at the outer band. In lieu of excavating and replacing the culvert, which would require excavation adjacent existing redwood trees, Caltrans' Construction has identified a new alignment for the culvert. The new alignment will drain creek flow to the approx. southern limit of the rock slope protection. Energy dissipation will be provided as necessary to limit erosion. A new culvert will be placed along or near the existing alignment, down drain replacement and RSP will be placed. A flared inlet in lieu of a headwall will be placed. A downdrain will require an anchored system.
This project involves restoring existing roadway structures and replacing the existing culvert structure and incorporate energy dissipation below the roadway to decrease future degradation with de minimus increase in fill. The project will not result in an expansion of the existing use.