Confronting Engineering Challenges Head On

City of San Diego Mount Soledad Road Landslide

Ninyo & Moore evaluated the October 3, 2007 landslide on Soledad Mountain Road in La Jolla, California for the City of San Diego. The project presented numerous issues for the geotechnical investigation including access for our drilling equipment to the slide area and adjacent properties; locally unstable surface soils, unstable geologic bedding and other subsurface conditions that made downhole logging potentially hazardous; coordination with numerous stakeholders (City, homeowners, insurance, contractors); and a critical time schedule to evaluate the causes of landslide reactivation and provide recommendations to temporarily and permanently stabilize the hillside and re-open Soledad Mountain Road, a major artery, for traffic. Our investigation was time-critical because the interim slide stabilization needed to be implemented prior to the onset of winter rains.

Our field evaluation included drilling of large-diameter borings, which were downhole logged by engineering geologists to evaluate landslide geometry and characteristics. Simultaneously, small diameter borings were used to obtain hundreds of samples for soil moisture and other testing in order to identify if water from existing utilities and other sources could have been a contributing factor to slide reactivation. Our laboratory tested over 2,500 samples in support of the evaluation. Construction repairs utilized a combination of grading, reinforced concrete shear pins, geofabrics and drainage improvements for stabilization.