LA CIENEGA BLVD. LANDSLIDE STABILIZATION PROJECT EXPOSES NEWPORT-INGLEWOOD FAULT ZONE, BALDWIN HILLS, LOS ANGELES COUNTY, CALIFORNIA

Mitigative grading for surficial instablility of the northwest-facing natural slope above the northbound lanes of La Cienega Blvd. exposed 120 vertical feet of the Newport-Inglewood fault zone. The grading was intended to eliminate debris flows, originating on the slope, from occurring and closing La Cienega Blvd. during storms, a recurrent process at this location. Following a geotechnical investigation, Los Angeles County Department of Parks and Recreation, the owner of the slope, chose new technology to solve the problem. A 150-foot high, 6-foot wide, 1½:1 compacted, terraced fill, reinforced with GeoFibers manufactured by Synthetic Industries, was constructed using standard techniques. “Geofibers” are three-inch long polypropylene strands. When mixed into the fill, the fibers open into a net or grid configuration that mechanically reinforces the soil. Use of this material to improve shear strength for surficial instability has been successful elsewhere, but is new to Los Angeles County, and thus the project is considered an experimental pilot project by LACDPW. Adverse sedimentary structure and the active Newport-Inglewood fault zone precluded design for long-term gross stability. The 70 foot wide northwest trending fault zone displaces two Quaternary marine formations, the older Inglewood Formation, consisting of thin to moderately bedded siltstone and claystone with subordinate sandstone beds, over the loose to moderately dense Culver Sand to the south.

The opinions expressed are solely those of the authors, and do not represent the opinions of, nor endorsement by, the LACDPW.