Soil Engineering construction

San Mateo County Public Works Back to Projects

    Project: Landslide Stabilization

    In 1996 a landslide developed across the native hillside of an older residential development in La Honda California. Eventually the slide covered 20 acres, destroyed ten homes, and displaced two roadways. Subsequent subsurface geotechnical investigations by the US Geologic Survey, Cotton Shires & Associates, Parik Geotechnical and Upp Geotechnical defined subsurface conditions and provided design parameters for appropriate mitigating measures.

    The San Mateo County Public Works Department and their design team, working in concert with the Home Owners Association, negotiated a turnkey design/construct contract with Soil Engineering Construction, Inc. (SEC).

    The resulting construction plans, provided by SEC, divided the required slope stabilization work into two primary tasks. Task one, stabilize the slide mass with a deep subdrain that incorporated even deeper pressure relief wells and two lines of stitch piers with connecting grade beams and tiebacks. The "structural approach" was elected due to the elimination of the risks involved in making the cuts associated with an earthwork repair and its significant cost advantage. Task two, the stabilization of the slide scarp was addressed with slopping shear keys connected with large diameter drilled piers/shear pins. Again, high capacity tiebacks provided lateral restraint.

    The work, completed by Soil Engineering Construction, Inc. over a 12 month period involved the installation of more than 100 deeply founded, high capacity, double erosion protected tiebacks, over one hundred 3' diameter, 40' deep CIDH hole piers and the excavation and compaction of 10,000 cubic yards of engineered fill.