Arroyo Avenue Landslide

Ninyo & Moore provided geotechnical consulting services during and after the Arroyo Avenue landslide of January and February, 2005. The landslide involved 6 homes that were ultimately demolished and threatened 11 more during heavy winter rains. Ninyo & Moore was on site after movement began to provide the local city interim recommendations to slow or halt landslide movement. Recommendations included provision for the installation of 49 horizontal drains drilled during active movement. Ninyo & Moore subsequently performed a preliminary evaluation of the cause and extent of the landslide. The evaluation was performed to formulate recommendations for a short-term repair to improve the stability of the landslide through the 2005/2006 winter rain season. Services included research and review of background information such as pertinent existing geotechnical literature, aerial photographs, and topographic and geologic maps; geologic mapping of the landslide; drilling and downhole logging of six large-diameter borings; laboratory testing of landslide materials; and preparation of an illustrated report. In addition, Ninyo & Moore coordinated the preparation of interim repair plans and observed the interim repair work, which included regrading the surface of the slide, repairing surface drainage, and installation of a deep French drain above the landslide to intercept groundwater.