Proposed criteria for interpreting stability of lakeshore bluffs: Fid-Bau Portal

Proposed criteria for interpreting stability of lakeshore bluffs

Edil, T.B. / Haas, B.J.

Abstract The stability of the bluffs along the Lake Michigan shoreline in eastern Wisconsin has been assessed. The geotechnical properties of the bluff materials which can be broadly grouped as glacial tills, lacustrine silts and clays, and sandy outwash, have been determined and related to the failure phenomena seen in the bluffs. Two separate criteria have been proposed to help interpret the state of stability of these extremely active bluffs. The ‘critical circle’ criterion defines the failure in terms of the circle having the smallest safety factor and describes the process of lakeshore bluffs as being a succession of small rotational slides which retrogress from the toe to the top of the bluff. The ‘unstable circle’ criterion, on the other hand, assumes the failure to occur throughout the zone enveloped by the largest circle indicating a safety factor less than unity and may be thought of as a culmination of critical circles that fail approximately the same time. These criteria allow the recognition of slope evolutionary phenomena likely to take place in the bluffs. The effect of various parameters on these two criteria has also been investigated, by examining specific profiles encountered along the Lake Michigan shoreline. Finally, some examples of general coastal bluff conditions in the eastern Wisconsin counties are presented.