Scope of Work: The geotechnical investigation is focused on assessing the stability of the existing roadway, the fill embankment, and underlying native soils without modifying the current roadbed grade. The work includes historical documentation review, Lidar interpretation, subsurface exploration, and installation of monitoring instrumentation. Findings will inform geotechnical recommendations to support the design and construction of geotechnical measures intended to enhance long-term slope stability along the roadway corridor.

• Key Activities:

• Reviewed historical documentation, including records of past slope failures (1984, 1996, 1999) and geologic hazard mapping

• Evaluated Lidar imagery to assess surface features and potential landslide zones

• Identified prehistoric landslide features potentially impacting proposed access road

• Documented ongoing slope movement with monitoring instrumentation

• Performed detailed geotechnical evaluation of slope stability and roadbed conditions

• Planned and executed a subsurface boring program, including:

  • 10 geotechnical borings

  • 5 borings instrumented with slope inclinometers

  • 2 borings completed as piezometers for groundwater observation

• Evaluated stability of in-place fill and native soils supporting the roadway

• Interpreted slope inclinometer data indicating creep to depths of 20 feet

Results: CES’s geotechnical team developed recommendations for roadway stabilization and improvement on existing roadway, and provided input which will support the retaining wall design and embankment systems.