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The San Francisco Bay Region is bounded by distinctive mountains including the Santa Cruz Mountain Range and the Diablo Range. These mountains are constantly shaped by erosion and landslide activity. Homes and structures built in these hillside environments may be susceptible to landsliding. Landslides cause $1-2 billion in damage and more than 25 fatalities on average each year within the United States.
Several different types of landslides and landslide hazards may impact projects in hillside terrain such as deep-seated bedrock landslides, shallow soil slumps, or rapid-moving debris flows. Landslides may be active, dormant, or old and relatively stable. The relative age of landslides may be inferred by the morphology or shape of landslide features. Landslides can be triggered, or old landslides may be reactivated, in response to grading activities, to prolonged rainfall, or to seismic shaking on nearby active faults.
Counties and Cities may require Landslide Investigations to determine if landslides pose a hazard to proposed developments in hillside environments. Recently-adopted State regulations may also require landslide investigations.
I can design a Landslide Investigation for your project to satisfy requirements of regulatory agencies. The investigation may include excavation of test pits or borings to confirm the presence or absence of landsliding. Large diameter borings, designed to safely lower a geologist into a borehole to log and sample subsurface materials, may be utilized. Slope stability analysis may be necessary to assess the potential for reactivation of old and dormant landslides. Soil dating techniques may be employed to determine the age of landslide events, if possible.
The scope of the Landslide Investigation will be designed to meet the State, County, and City requirements for your project and may include:
- review of geologic maps, literature, and air photos,
- site reconnaissance and mapping,
- consultation with the Reviewing Geologist,
- consultation with the project Engineers and Architects,
- excavation and logging of test pits and borings,
- drafting and report preparation.
The Landslide Investigation will produce detailed logs, a site geologic map, and geologic cross-sections which define the limits and geometries of identified landslides and assess the risk to proposed improvements. Appropriate setbacks or mitigations and landslide repairs will be recommended where feasible.