Geotechnical Investigation of a Large Landslide in Somis, California

During the El Nino wet winter of 1998, a large deep-seated bedding plane landslide occurred in the Somis area of Ventura County, California. The landslide was approximately 740 feet long and 370 feet wide and occurred in the Pliocene-age Pico Formation. The elevation difference between the top and toe of the slide was approximately 210 feet. 

Antenna sites and an access road were significantly displaced. Movement of portions of the slide ranged from approximately 33 feet to 70 feet. If the slide was not stabilized, additional movement could have affected other antenna sites and a building near the toe of the slide.

Gorian and Associates, Inc. performed a detailed geologic and geotechnical investigation of the slide involving drilling and sampling 6 borings to depths of 35 feet to 79 feet within the slide mass. Groundwater encountered within the slide mass added difficulty to the field investigation. Detailed laboratory testing and engineering analyses were performed to develop recommendations to stabilize the slide. The landslide was repaired by complete removal and recompaction of the slide mass. Gorian and Associates, Inc. also provided engineering geology and construction inspection services during the landslide repair.

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