Clay Chemistry and Slope Stability

The East Bay hills of Contra Costa County, California, east of Berkeley and Oakland, are well known for unstable soil conditions and numerous slope failures are observed each year during the rainy season. The susceptibilty of specific areas of failure often is not predictable based on usual soil engineering considerations. An investigation has been made, therefore, to determine whether the soil chemistry of several samples from failure areas is such as to indicate a high susceptibility to dispersion. Samples from five of the 16 sites where unstable slopes exist had unfavorable pore solution chemistry relative to their susceptibility to dispersion. The data are insufficient to establish conclusively that slope failures in these areas were caused as a result of strength loss due to clay dispersion. Further study of the possibility appears warranted.