Geotechnical Challenges in the Bay Area

Geotechnical Challenges in
The Unique San Francisco Bay Area

In many parts of the United States the geologic conditions are relatively uniform and the demand for soil engineering is relatively low. In these areas, architects, civil and structural engineers can rely upon the Uniform Building Code for conservative soil design criteria for most projects. This is not the case in the Bay Area and relying upon the building code alone can lead to problems.

The geology of the greater Bay Area is very complex and almost every geologic hazard on our planet occurs in this very relatively tiny area.

The primary geologic hazards are earthquakes that occur on the San Andreas and other associated fault systems. When earthquakes occur in the bay area, other secondary hazards (that often are not present in other parts of the country) can be triggered. Earthquake induced landslides can occur on our steeper hillsides. Rockfalls can also occur in areas where fractured rock is present on steep slopes. Soil settlement (usually loose sands) can be caused by seismic shaking. Lateral ground spreading can take place, as it did during the 1906 and 1989 earthquakes. Liquefaction (where loose sandy soil under the groundwater table looses all strength) also is a phenomenon that occurs. Parts of the Bay Area are also susceptible to Tsunamis. All of these, and more, secondary hazards can occur during a Bay Area earthquake. In other parts of the country, that have less complicated topography and geology, earthquakes pose much less of a hazard.

Our hillsides are often mantled with gravity deposited soil, or weak fractured bedrock that has weathered into soil. Our climate is such that the wetting and drying of the soil seasonally often weakens it over time making certain areas susceptible to mud flows and landslides. Much of our country is not steep enough for sliding to be a consideration.
Our bayside areas often contain landfill, placed decades ago over soft and very compressible bay mud deposits. When structures or additional fills are placed in these areas consolidation settlement occurs. This phenomenon only occurs in limited areas in our country.

Much of our land is blanketed by soil having a high clay content. The clay mineral in the soil has an affinity for water and when the two are mixed the soil swells. Expansive soil is present in many areas of the United States, but of course, we have expansive soil problems throughout much of the Bay Area.

Our coastal areas are gradually eroding into the Pacific Ocean. The rate of retreat of our coastal bluffs varies, primarily based upon the materials that compose the cliff tops and the direction and forces of ocean waves. Again, this hazard is not present in most parts of the United States. We, of course, have this natural geologic hazard.
In summary, geotechnical engineering in the Bay Area is much more challenging than in most parts of the country. In some states if you say “soil engineer” no one would have an idea of what role they would play in a project. No wonder that academic institutions, such as U.C. Berkeley attract soil engineering students from throughout the world to learn about soil mechanics in this most unique area.