City of Daly City retained CE&G to evaluate the geotechnical and geologic conditions along the proposed access road realignment. Severe winter storms in 1997/98 damaged a 30-inch diameter corrugated metal storm drain pipe in the canyon causing substantial erosion at the point of the pipe break. The eroded slopes removed a portion of Avalon Drive and threatened part of the adjacent residential development that surrounds the rim of the canyon.
Previous repairs consisted of demolishing a threatened church at the southern rim of the canyon and removing 400,000 cubic yards of the unstable southwest bluff and placing it in the canyon for stability. The design included a new high density polyethylene (HDPE) piping and energy dissipator system, two sediment basins, surface and subsurface drainage systems, an access road, slope protection, revegetation, and restoration of Avalon Drive. A subsequent pipe break led to further erosion and undermining of the lower portion of the access road.
CE&G was tasked with evaluating the conditions along the potential access road relocation alignment, taking into consideration the previous failures in the area and the geologic setting. We completed a geotechnical investigation including soil borings, installation of inclinometers and vibrating wire piezometers, laboratory testing, engineerign analyses and prparation of a geotechninal report with recommedations for design and construction.