This project was a study for Caltrans to investigate the engineering feasibility and estimated cost for constructing an approximately 4,000-foot long automobile bypass tunnel to replace the existing unstable State Highway 1 roadway along the coast at Devil's Slide in San Mateo County.
Client:
California Department of Transportation
Location:
San Mateo County, CA
AGS scope of work consisted of performing a geologic investigation to provide the subsurface data necessary as a basis for selecting the most appropriate tunneling technique, designing the permanent tunnel, and estimating the construction cost.
AGS personnel prepared a detailed geologic map of the area, and supervised and performed all field activities in remote and very rugged terrain. The field activities consisted of drilling and logging 14 rock core borings to a maximum depth of 700 feet, with up to three drill rigs working simultaneously for twenty hours per day. The borings were vertical, inclined at various angles, and horizontal. Temporary roads had to be constructed to reach the more remote drilling locations. Several piezometers were installed, as well as an electronic strain gauge and a 700-foot deep inclinometer. Packer tests and down-hole geophysical surveys were performed in selected holes. Significant effort was made to identify landslide deposits and assess landslide hazard affecting the proposed tunnel route. At the completion of the work, AGS supervised site restoration.
